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WAAS Services

2026-04-19T21:55:45Z

Gema.Cueto: Updated reference ICD/SDD links

{{Article Infobox2
|Category=WAAS
|Editors=GMV
|Level=Basic
|YearOfPublication=2011
|Logo=GMV
|Title={{PAGENAME}}
}}
The Wide Area Augmentation System ([[WAAS General Introduction|WAAS]]) is the United States [[SBAS General Introduction|Satellite Based Augmentation System]]. The programme, started in 1992, is being carried out and operated by the [http://www.faa.gov/ Federal Aviation Agency (FAA)]<ref name="FAA_NAV_HISTORY">[http://www.faa.gov Navigation Services - History - Satellite Navigation,] [http://www.faa.gov/ FAA.]</ref> and is specially developed for the civil aviation community.<ref name="FAA_WAAS">[http://www.faa.gov/about/office_org/headquarters_offices/ato/service_units/techops/navservices/gnss/waas/ Navigation Services - Wide Area Augmentation System (WAAS)], [http://www.faa.gov/ FAA.]</ref> The system, which was declared operational in late 2003,<ref name="STANFORD_WAAS">[https://gps.stanford.edu/research/currentcontinuing-research/waas-sbas Wide Area Differential GPS (WADGPS), Stanford University]</ref> currently supports thousands of aircraft instrument approaches in more than one thousand airports in USA and Canada.<ref name="APPROACHES">[http://www.faa.gov/about/office_org/headquarters_offices/ato/service_units/techops/navservices/gnss/approaches/index.cfm GNSS - GPS/WAAS Approaches,] [http://www.faa.gov/ Federal Aviation Agency (FAA).]</ref> WAAS service area includes CONUS, Alaska, Canada and Mexico.<ref name="WAASExpanded">[http://www.faa.gov/about/office_org/headquarters_offices/ato/service_units/techops/navservices/gnss/waas/news/ WAAS Service Expanded into Canada and Mexico, September 28, 2007,] [http://www.faa.gov/ Federal Aviation Agency (FAA).]</ref> The WAAS programme is continuously in evolution; three development phases have been already covered, and there are on-going plans to improve the capability of the system in parallel with the evolution of the SBAS standards towards a dual-frequency augmentation service.<ref name="EXTENSION">[http://www.faa.gov/about/office_org/headquarters_offices/ato/service_units/techops/navservices/gnss/library/satnav/media/SatNav_March08.pdf SatNav News, Vol. 33, March 2008,] [http://www.faa.gov/ Federal Aviation Agency (FAA).]</ref>

It currently achieves excellent coverage over the vast majority of North America, providing corrections to the GPS L1 signal. However, when the ionosphere is disturbed or when the constellation is weak, its availability may be reduced. Using both the L1 and L5 signals in the aircraft will remove the primary dependence on the state of the ionosphere. Removing this largest source of uncertainty allows service to be provided under more conditions than are allowed today. Thus, the use of L1 and L5 together as it is being defined in the evolution of SBAS standards will provide very robust coverage of vertical guidance.<ref name="article">[https://www.researchgate.net/profile/Todd_Walter/publication/261537494_Evolving_WAAS_to_serve_L1L5_users/links/5a6a0f5c4585154d15466882/Evolving-WAAS-to-serve-L1-L5-users.pdf Todd Walter, Juan Blanch, R. Eric Phelts, and Per Enge, "Evolving WAAS to Serve L1/L5 Users", Stanford University, 2020]</ref>

==WAAS Services==
[[File:Airports_with_wass_supported_approaches.jpg‎ |CONUS airports with WAAS procedures.|300px|thumb|right]]
[[File:Alaska_Airports_with_WAAS_approches.jpg‎ |Alaska airports with WAAS procedures.|300px|thumb|right]]

The objectives of the WAAS are to provide improved [[Integrity|integrity]], [[Accuracy|accuracy]], [[Availability|availability]], and [[Continuity|continuity]] of service to the [[GPS Services|GPS Standard Positioning Service]] (SPS) for the Civil Aviation community. The ultimate objective is to provide a navigation system for all phases of flight through precision approach.<ref name=SpecWAAS>[http://www.faa.gov ''Specification for the Wide Area Augmentation System(WAAS)''], FAA-E- 2892b, August 13, 2001.</ref>

The WAAS is a safety-critical system which augments Global Positioning System (GPS) Standard Positioning Service (SPS). The WAAS provides a signal-in-space to WAAS users, i.e. all aircraft with approved WAAS avionics, to support en route through precision approach navigation. The WAAS GEO satellites have ranging capabilities, i.e., they can be used as extra GPS satellites to enhance the performance achieved in the user location because of the additional statistics and the improved geometry. In addition, the WAAS signals broadcast augmentation information that corrects GPS ephemeris and ensures the integrity meeting the [[WAAS Performances|WAAS performance requirements]].<ref name=SpecWAAS/><ref>[https://archive.gps.gov/technical/ps/2008-WAAS-performance-standard.pdf WAAS Performance Standard]</ref>

In order to take benefit from the signal in space provided by WAAS, aircraft need to be equipped with certified receivers meeting the corresponding standards, i.e. RTCA MOPS DO 229 for current WAAS services or the future SBAS DFMC standards for next evolutions of WAAS (see article [[SBAS Standards]]).

On July 10, 2003, the WAAS system was declared operational for safety-of-life aviation, with a service area consisting in 95% of the United States, and part of Alaska,<ref name="STANFORD_WAAS"/><ref>[http://en.wikipedia.org/wiki/Wide_Area_Augmentation_System Wide Area Augmentation System in Wikipedia]</ref> to be expanded in 2007 to include Canada and Mexico.<ref name="EXTENSION"/> At present, WAAS supports en-route, terminal and approach operations down to a full LPV-200 (CAT-I like Approach Capability) for the WAAS service area that includes CONUS, Alaska and Canada.<ref name="APPROACHES"/><ref name="WAASExpanded"/>

Currently, WAAS supports the following flight procedures, as well as airport departures and airport arrivals:<ref name="APPROACHES"/><ref>[http://aviationglossary.com Aviation Glossary]</ref>
* LNAV (Lateral Navigation).
* LNAV/VNAV (Lateral Navigation/Vertical Navigation).
* LP (Localizer Performance).
* LPV (Localizer Performance with Vertical guidance).

The WAAS service is interoperable with other regional SBAS services, including those operated by Japan (MSAS), Europe (EGNOS), and India (GAGAN).

==Notes==
<references group="footnotes"/>
==References==
<references/>

[[Category:WAAS]]

WAAS Performances

2026-04-19T21:53:38Z

Gema.Cueto: Updated reference ICD/SDD links

{{Article Infobox2
|Category=WAAS
|Editors=GMV
|Level=Basic
|YearOfPublication=2011
|Logo=GMV
|Title={{PAGENAME}}
}}
The Wide Area Augmentation System ([[WAAS General Introduction|WAAS]]) is the United States [[SBAS General Introduction|Satellite Based Augmentation System]]. The programme, started in 1992, is being carried out by the [http://www.faa.gov/ Federal Aviation Agency (FAA)]<ref name="FAA_NAV_HISTORY">[http://www.faa.gov Navigation Services - History - Satellite Navigation,] [http://www.faa.gov/ FAA.]</ref> and is specially developed for the civil aviation community.<ref name="FAA_WAAS">[http://www.faa.gov/about/office_org/headquarters_offices/ato/service_units/techops/navservices/gnss/waas/ Navigation Services - Wide Area Augmentation System (WAAS)], [http://www.faa.gov/ FAA.]</ref> The system, which was declared operational on July 10, 2003on July 10, 2003,<ref name="STANFORD_WAAS">[https://gps.stanford.edu/research/currentcontinuing-research/waas-sbas Wide Area Differential GPS (WADGPS), Stanford University]</ref> currently supports thousands of aircraft instrument approaches in more than one thousand airports in USA and Canada.<ref name="APPROACHES">[http://www.faa.gov/about/office_org/headquarters_offices/ato/service_units/techops/navservices/gnss/approaches/index.cfm GNSS - GPS/WAAS Approaches,] [http://www.faa.gov/ Federal Aviation Agency (FAA).]</ref> WAAS service area includes CONUS, Alaska, Canada and Mexico.<ref name="WAASExpanded">[http://www.faa.gov/about/office_org/headquarters_offices/ato/service_units/techops/navservices/gnss/waas/news/ WAAS Service Expanded into Canada and Mexico, September 28, 2007,] [http://www.faa.gov/ Federal Aviation Agency (FAA).]</ref> The WAAS programme is continuously in evolution; three development phases have been already covered, and there are on-going plans to improve the capability of the system in parallel with the evolution of the SBAS standards towards a dual-frequency augmentation service.<ref name="EXTENSION">[http://www.faa.gov/about/office_org/headquarters_offices/ato/service_units/techops/navservices/gnss/library/satnav/media/SatNav_March08.pdf SatNav News, Vol. 33, March 2008,] [http://www.faa.gov/ Federal Aviation Agency (FAA).]</ref>, <ref name="STANFORD_WAAS"/>
==WAAS Performance==
Satellite Based Augmentation Systems ([[SBAS General Introduction|SBAS]]) performances are usually described in terms of [[Integrity|integrity]], [[Accuracy|accuracy]], [[Availability|availability]], and [[Continuity|continuity]].
According to the WAAS performance standard,<ref name=WAAS_PSTD>[https://archive.gps.gov/technical/ps/2008-WAAS-performance-standard.pdf Global Positioning System Wide Area Augmentation System (WAAS) Performance Standard,] Department of Transportation and Federal Aviation Administration, USA, 1st Edition, 31 October 2008.</ref> WAAS service area is divided in five coverage zones:
*Zone 1: CONUS.
*Zone 2: Alaska.
*Zone 3: Hawaii.
*Zone 4: Puerto Rico and some other Caribbean islands.
*Zone 5: US territory excluding zones 1 to 4.
The volume covered includes a region up to 100.000 feet above the surface. For zones 1 to 3, the area extends up to 30 nm outside the land.

<gallery perrow="5">
Image:WAAS_zone_1.jpg | Zone 1
Image:WAAS_zone_2.jpg | Zone 2
Image:WAAS_zone_3.jpg | Zone 3
Image:WAAS_zone_4.jpg | Zone 4
Image:WAAS_zone_5.jpg | Zone 5
</gallery>

WAAS specification distinguishes the following flight phases:<ref name=WAAS_PSTD/>
*En route
*Terminal
*LNAV (Lateral Navigation)
*LNAV/VNAV (Lateral Navigation/Vertical Navigation)
*LPV (Localizer Performance with Vertical guidance)
*LPV 200 (LPV 200 foot minimum)

The requirements considering the different flight phases and coverage zones are summarised in the next table:<ref name=WAAS_PSTD/>

{| class="wikitable" align="center"
|+align="bottom" |''WAAS Navigation Performance Requirements''
!
! En Route
! Terminal
! LNAV
! LNAV/VNAV
! LPV
! LPV 200
|- align="center"
! TTA
| 15 s
| 15 s
| 10 s
| 10 s
| 6.2 s
| 6.2 s
|- align="center"
! HAL
| 2 nm
| 1 nm
| 556 m
| 556 m
| 40 m
| 40 m
|- align="center"
! VAL
| N/A
| N/A
| N/A
| 50 m
| 50 m
| 35 m
|- align="center"
! Probability of HMI
| 10-7 per hour
| 10-7 per hour
| 10-7 per hour
| 2 x 10-7 per approach
| 2 x 10-7 per approach (150 seconds)
| 2 x 10-7 per approach (150 seconds)
|- align="center"
! Zone 1 Continuity
| 1 - 10-5 per hour
| 1 - 10-5 per hour
| 1 - 10-5 per hour
| 1 - 5.5 x 10-5/15 seconds
| 1 - 8 x 10-6/15 seconds
| 1 - 8 x 10-6/15 seconds
|- align="center"
! Horizontal Accuracy (95%)
| 0.4 nm
| 0.4 nm
| 220 m
| 220 m
| 16 m
| 16 m
|- align="center"
! Vertical Accuracy (95%)
| N/A
| N/A
| N/A
| 20 m
| 20 m
| 4 m
|- align="center"
! Availability (Zone 1 Coverage)
| 0.99999 (100%)
| 0.99999 (100%)
| 0.99999 (100%)
| 0.99 (100%)
| 0.99 (80-100%)
| 0.99 (40-60%)
|- align="center"
! Availability (Zone 2 Coverage)
| 0.999 (100%)
| 0.999 (100%)
| 0.999 (100%)
| 0.95 (75%)
| 0.95 (75%)
| N/A
|- align="center"
! Availability (Zone 3 Coverage)
| 0.999 (100%)
| 0.999 (100%)
| 0.999 (100%)
| N/A
| N/A
| N/A
|- align="center"
! Availability (Zone 4 Coverage)
| 0.999 (100%)
| 0.999 (100%)
| 0.999 (100%)
| N/A
| N/A
| N/A
|- align="center"
! Availability (Zone 5 Coverage)
| 0.99999 (100%)
| 0.999 (100%)
| 0.999 (100%)
| N/A
| N/A
| N/A
|}

In this table, the integrity requirements are given as the probability of HMI, namely Hazardously Misleading Information. In addition to integrity, accuracy, availability and continuity, the table shows the specification for Time To Alert (TTA) and for Horizontal and Vertical Alert Limits (HAL and VAL).

On July 10, 2003, the WAAS system was certified for safety-of-life aviation, covering 95% of the contiguous U.S. and part of Alaska <ref name="STANFORD_WAAS"/><ref>[http://en.wikipedia.org/wiki/Wide_Area_Augmentation_System Wide Area Augmentation System]</ref>. At present, WAAS supports en-route, terminal and approach operations down to a full LPV-200 (CAT-I like Approach Capability) for the CONUS, Mexico and Canada.

The FAA publishes real time WAAS performance at the [http://www.nstb.tc.faa.gov Technical Center WAAS Test Bed web site].<ref name="WTB"/> Typical performances provided by WAAS System when considering operating in LPV (Horizontal Alarm Limit = 40 m , Vertical Alarm Limit =50 m) are shown in next figure:<ref name="WTB">[http://www.nstb.tc.faa.gov/24Hr_WaasLPV200.htm FAA Monitoring WAAS Performances in Real-Time]</ref>

[[File:WAAS_performance.png|center|thumb|400px|WAAS LPV Coverage<ref>[https://www.nstb.tc.faa.gov/24Hr_WaasLPV.htm WAAS LPV performance in Federal Aviation Administration website]</ref>]]

==Notes==
<references group="footnotes"/>
==References==
<references/>

[[Category:WAAS]]

EGNOS Performances

2026-04-19T21:45:35Z

Gema.Cueto: Updated reference ICD/SDD links

{{Article Infobox2
|Category=EGNOS
|Editors=GMV
|Level=Basic
|YearOfPublication=2011
|Logo=GMV
|Title={{PAGENAME}}
}}
EGNOS (European Geostationary Navigation Overlay Service) is the European satellite-based augmentation service (SBAS) that complements the existing satellite navigation services provided by the US [[GPS General Introduction|Global Positioning System]] (GPS) using the L1 C/A signal. EGNOS will augment both GPS and Galileo in the future (in EGNOS V3) using L1 and L5 frequencies.

EGNOS [[GNSS Performances|performances]] are usually described in terms of [[Accuracy|accuracy]], [[Integrity|integrity]], [[Availability|availability]] and [[Continuity|continuity]].

==EGNOS Performances Requirements==
EGNOS has been designed to meet SBAS performance requirements for civil aviation operations down to Localizer Performance with Vertical Guidance (LPV) minima but EGNOS service might also be used in a wide range of other application domains (e.g. maritime, rail, road...):<ref name="SOL DEF">[https://egnos.gsc-europa.eu/sites/default/files/documents/egnos_sol_sdd_in_force.pdf?v=1726657048 EGNOS Safety of Life Service Definition Document]</ref><ref name=" EGNOS OS SDD">[https://egnos.gsc-europa.eu/sites/default/files/documents/egnos_os_sdd_in_force.pdf?v=1743425975 EGNOS Open Service Definition Document]</ref>

{| class="wikitable"
|-
! rowspan="2" | Service
! rowspan="2" | Service Coverage
! colspan="2" | [[Accuracy]] (95%)
! colspan="4" | [[Integrity]]
! rowspan="2" colspan ="2" | [[Continuity]]
! rowspan="2" | [[Availability]]
|-
! Lateral
! Vertical
! Integrity
! colspan="3" | TTA
|-
! [[EGNOS Open Service|Open Service]]
| EU25 States (plus Norway and Switzerland) land masses
| align="center" | 3m
| align="center" | 4m
| align="center" colspan="2" | -
| align="center" colspan="2" | -
| align="center" colspan ="2"| -
| align="center" | 0.99
|-
! [[EGNOS Safety of Life Service|En-route and NPA]]
| |FIRs of ECAC 96
| align="center" | 220m
| align="center" | -
| align="center" colspan="3" | 1 – 1x10⁻⁷/h
| align="center" | Less than 6 seconds
| align="center" | <1 – 1x10⁻³ per hour in most of ECAC || <1 – 2.5x10⁻³ per hour in other areas of ECAC
| align="center" | 0.999 in all ECAC
|-
! [[EGNOS Safety of Life Service|APV-I & LPV200]]
| Land Masses of ECAC 96
| align="center" | 3m
| align="center" | 4m
| align="center" colspan="3" | 1 – 2x10⁻⁷/approach
| align="center" | Less than 6 seconds
| colspan="1" align="center" | <1 – 1x10⁻⁴ per 15 seconds in the core of ECAC || 1 –5x10⁻⁴ per 15 seconds in most of ECAC landmasses
| align="center" | 0.99 in most of ECAC landmasses
|}

<gallery widths="250px" heights="200px">
Image:EGNOS_performances_ECAC_FIR96.png|‎‎ECAC 96 Flight Information Regions
Image:EGNOS_performances_ECAC_land_masses.png|‎ECAC 96 land masses
</gallery>

==Typical Performances==
The typical performances provided by EGNOS are presented in the next figures. For the computation, the day 6th December 2018, considered to be a representative day, has been selected. The images have been obtained using gmvBrave tool.<ref name="gmvBrave">[https://www.gmv.com/en/Products/brave/ gmvBrave]</ref>

<gallery widths="500px" heights="300px" perrow="1">
Image:EGNOS_availability.jpg‎|'''Availability:''' The figure shows EGNOS availability map together with the iso-lines of availability compliance to APV-I service level availability requirements (i.e., HPL < 40 m and VPL < 50 m). The period of analysis corresponds to one day with the inner iso-line delimiting the user locations where a service level over 99% availability is achieved.
Image:EGNOS_continuity.jpg|'''Continuity:''' The figure shows EGNOS continuity map together with the iso-lines of continuity risk compliance to APV-I service level. The continuity risk is computed as the probability of having a continuity event (Protection Levels bigger than Alarm Limits) during a period of 15 seconds provided that the service was available (Protection Levels smaller than Alarm Limits) at the start of the period. The inner iso-line, 1e-4, delimits the user locations which did not have a single continuity event during the analyzed day.
Image:EGNOS_accuracy.jpg|'''Accuracy:''' The figure shows EGNOS vertical accuracy map together with the iso-lines of 95% Vertical Position Error in metres. Users inside the inner iso-line had a vertical accuracy below 2 m (95%) for the analyzed day.
Image:EGNOS_integrity.jpg|'''Integrity:''' The figure shows EGNOS vertical integrity margins as maximum Vertical Safety index map (maximum ratio between the vertical user error and the vertical user protection level). All values are under one meaning that no integrity failures at user level were observed.
</gallery>

==Monitoring of EGNOS Performances==
EGNOS performances are being monitored continuously by several entities, such as ESSP<ref name="ESSP EGNOS Perfo">[https://egnos-user-support.essp-sas.eu/new_egnos_ops/ EGNOS performances by ESSP]</ref> and ESA.<ref name="ESA EGNOS Perfo">[http://www.egnos-pro.esa.int/IMAGEtech/imagetech_realtime.html EGNOS performances by ESA]</ref>

The EGNOS performance monitoring done by ESSP<ref name="ESSP EGNOS Perfo"/> includes figures on achieved availability, continuity and integrity. In addition, it forecasts the performances in terms of availability and integrity.

The monitoring done by ESA<ref name="ESA EGNOS Perfo"/> is twofold. On the one hand, the messages, as broadcast by the EGNOS satellites, are analyzed to determine the status of several parameters, such as the GPS satellites which are augmented by EGNOS, the level of monitoring of the ionosphere over Europe or the achieved protection levels. On the other hand, ESA monitoring environment allows to select different reference stations and depicts the accuracy and integrity obtained for those sites.

==Notes==
<references group="footnotes"/>
==References==
<references/>

[[Category:EGNOS]]
[[Category:EGNOS Performances]]

EGNOS Future and Evolutions

2026-04-19T21:43:11Z

Gema.Cueto: Updated reference ICD/SDD links

{{Article Infobox2
|Category=EGNOS
|Editors=GMV
|Level=Basic
|YearOfPublication=2011
|Logo=GMV
|Title={{PAGENAME}}
}}
The [[Wikipedia:European Commission|European Commission (EC)]] intends to ensure the future of [[EGNOS Services|EGNOS services]] for GPS L1 legacy users until at least 2030.<ref name="EGNOS SoL SDD">[https://egnos.gsc-europa.eu/sites/default/files/documents/egnos_sol_sdd_in_force.pdf?v=1726657048 EGNOS Safety of Life Service Definition Document]</ref> In this context, the budget should be secured to operate the system and manage the system obsolescence. Moreover, major EGNOS system evolutions (EGNOS V3) towards a multi frequency and multi constellation configuration are currently being assessed with the objective to have them operational by 2025.<ref name="EGNOS V3 contract">[https://www.airbus.com/newsroom/press-releases/en/2018/01/airbus-selected-by-esa-for-egnos-v3-programme.html Award of EGNOS V3 contract]</ref>

A technical assessment of the potential EGNOS evolution, EGNOS V3, is currently done by the European Space Agency within the European GNSS Evolution Programme. Airbus has been selected by the European Space Agency (ESA) as the prime contractor to develop EGNOS V3,<ref name="EGNOS V3 contract">[https://www.airbus.com/newsroom/press-releases/en/2018/01/airbus-selected-by-esa-for-egnos-v3-programme.html Award of EGNOS V3 contract]</ref> leading a consortium with partners from France, Germany, Spain and Switzerland. Airbus is responsible for the development, integration, deployment and preparation of EGNOS V3 operations, the overall performance of the system and the Central Processing Facility which is the heart of the real time navigation algorithms.
During the 6.5 year contract, around 100 people and 20 subcontractors will work on delivering the EGNOS V3 system. In 2023, the single frequency version will be available to replace the current operational version and, 18 months later, the final version in dual frequency will be delivered.
EGNOS is composed of a large network of about 50 ground stations deployed over Europe, Africa and North America, two master control centres located near Rome and Madrid, and a System Operation Support Centre in Toulouse. EGNOS will also use geostationary satellites navigation payload.<ref name="EGNOS V3 contract">[https://www.airbus.com/newsroom/press-releases/en/2018/01/airbus-selected-by-esa-for-egnos-v3-programme.html Award of EGNOS V3 contract]</ref>

==EGNOS Mission Roadmap and EGNOS Evolutions==
The European Parliament and the Council assigned the management of the EGNOS programme to the European Commission.<ref>[http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2008:196:0001:0011:en:PDF Regulation (EC) No 683/2008 of the European Parliament and of the Council of 9 July 2008 on the further implementation of the European satellite navigation programmes (EGNOS and Galileo)]</ref> On the other hand, ESA is the technical player responsible for system design
and development, and ESSP is the service provider.<ref name="Mid-term review">[http://europa.eu/rapid/press-release_MEMO-11-26_en.htm Mid-term review of the European satellite radio navigation programmes]</ref>

The European Commission, in its role of entity in charge of the management of the EGNOS programme, is defining the roadmap for the evolution of the EGNOS mission. This roadmap should cope with legacy and new missions:
*2011-2030: En-route / NPA / APV1 / LPV200 service based on augmentation of GPS L1 only. The [[EGNOS Safety of Life Service|Safety Of Life (SoL)]] service is being offered by EGNOS from early 2011 on a regional basis and this will be guaranteed up to 2030 in compliance with ICAO SBAS SARPS. The service is thus compliant with the aviation requirements for Approaches with Vertical Guidance (APV-I) and Category I precision approaches, as defined by ICAO in Annex 10. In order to grant this timeframe, it is still needed to achieve a programmatic commitment based on secured funds.
*2020+: It is planned that EGNOS will experiment a major evolution by 2025, EGNOS V3, including the fulfilment of the SBAS L1/L5 standard, expansion to dual-frequency, and evolution toward a multi-constellation concept.

To support this mission roadmap, EGNOS needs to evolve. This evolution is divided into minor updates of the current EGNOS version, EGNOS V2, and a major evolution leading to the provision of new services, EGNOS V3.

The minor evolutions in the current EGNOS version are performed in a regular basis at an approximate pace of an update per year, and aim at solving infrastructure obsolescence issues, at supporting the LPV200 service beyond APV1 and at improving the operation of the system.

The major evolution requires a full dedicated engineering cycle starting from the definition of the mission of the system highly coupled with a technical feasibility analysis in coordination with the evolution of the SBAS standards.

As regards the consolidation of the new EGNOS missions, the European Commission set up a consultative group of GNSS experts called the Mission Evolution Advisory Group (MEAG). MEAG aims at providing EC with independent advice and ''recommendations on potential evolutions of the mission objectives and the service definitions for the European satellite navigation programmes Galileo and EGNOS''.<ref>[https://ec.europa.eu/growth/content/call-applications-selection-new-members-mission-evolution-advisory-group-meag_es Mission Evolution Advisory Group (MEAG)]</ref>
The group is expected to critically assess changes of both user needs and scope of space-based PNT, both on European and international scale. Changes on the mission and service requirements for the Galileo and EGNOS programme may be analysed too, proposing suitable updates of the mission and service baseline.
MEAG members include experts from GNSS user communities, GNSS industry sectors, academia, national space agencies and other recognized experts from Member States. The MEAG meets on a regular basis with an indicative number of three meetings per year. The expert group may establish on an ad-hoc basis Working Groups to provide specialist support as required to carry out its activities. The MEAG shall further record and report its work results and recommendations on a yearly basis to the Commission.

As for the EGNOS technical evolution, ESA is managing several activities within the European GNSS Evolution Programme (see below). 
The European Commission and the European Space Agency are very active in the different international co-operation fora in [[SBAS Standards|SBAS standardisation]] and [[SBAS Interoperability|SBAS interoperability]] ensuring the co-ordination of the EGNOS evolution with that of the other [[SBAS Systems|SBAS in the world]].

On September 2015, after extensive ground and space testing, the SES-5 GEO satellite entered into the EGNOS operational platform, replacing Inmarsat-4F2. The satellite ensures reliable EGNOS services until 2026. It has been introduced through EGNOS System Release V241M, which enables a range of performance improvements.
<ref>[http://gpsworld.com/egnos-services-ensured-long-term-thanks-to-ses-5-geo-satellite/ EGNOS Services Ensured Long Term, Thanks to SES-5 GEO Satellite]</ref>

Changes in the EGNOS Space Segment configuration have been introduced in order to use the newest GEO satellites in detriment of the older ones. See [[EGNOS Space Segment | EGNOS Space Segment]] for details regarding the current operational platform.

==The European GNSS Evolution Programme==
The European GNSS Evolution Programme (EGEP) is an ESA optional programme supported by 17 Member States and Canada which was defined in 2006 by ESA to address the second generation of the EGNOS and Galileo systems.<ref name=" ESA SISNeT Portal">EGNOS Evolution Plans and the GNSS Evolutions Programme; R. Lucas Rodriguez, F. Toran, R. Dellago, B. Arbesser-Rastburg, D. Flament; Proceedings of the 2009 International Technical Meeting of The Institute of Navigation January 26 - 28, 2009.</ref>

Its primary aim is to undertake research and development in and verification of technologies relating to regional space-based augmentation systems (SBAS) and global navigation satellite systems (GNSS).
Through forward-looking activities, the programme ensures that European industry has timely availability of competitive and innovative capabilities required for the evolution of EGNOS and Galileo. This applies to future requirements in the short, medium and long term.

EGEP also provides a framework for scientific research enabled by GNSS, which spans a wide range of disciplines, from atmosphere and climate modelling through time and space references to fundamental physics.
The programme is being implemented through activities anchored in Work Plans that are being successively defined by the Agency and approved by the Participating States according to the following objectives: <ref>[https://www.esa.int/Our_Activities/Navigation/GNSS_Evolution/About_the_European_GNSS_Evolution_Programme About the European GNSS Evolution Programme]</ref>

*begin defining future system architectures for EGNOS and Galileo and prepare the technology for future versions of these systems
*support the definition of how to implement the next version of EGNOS, and prepare the technology for it
*provide testbeds and system tools
*improve Agency knowledge of GNSS performance monitoring and the principal environmental factors influencing performance
*promote and support scientific exploitation of EGNOS and Galileo

Among many other tasks, the first phase of this programme included two parallel studies about the concept of Multi-Constellation Regional System (MRS) over 2007-2009. An outcome of this work was a generic MRS architecture baseline that should be considered as a candidate target for V3 functional architecture and further assessed and refined within the EGNOS V3 phase A definition study.<ref name="EGNOS V3 SOW">Statement of Work EGNOS V3 Definition Phase, ESA-DTEN-NF-SoW/01281, Issue 1.0, 08/07/2010, ESA.</ref>

The second phase of EGEP on SBAS (over 2010-2011) was devoted to the consolidation of system evolutions and to field testing. It is broken down into three main parts:<ref name="EGNOS V3 SOW"/>
* EGNOS V3 Definition Phase, aiming at preparing the new EGNOS system generation to address obsolescence issues, robustness improvement, new services, standard evolutions, coverage extension, use of new broadcast means, with a view to start preparing the EGNOS V3 implementation phase at a later stage (post 2013).
* Experimentations with several Test-Beds based on using a complete or partial SPEED (Support Platform for EGNOS Evolutions & Demonstrations) infrastructure.
* SPEED related activities in order to procure, install, operate and maintain the SPEED V1 engineering platform allowing to run the above tests and to develop an upgraded version of SPEED V1 platform to implement new features in the Host Structure of SPEED necessary to support a second phase of experimentations (at a later stage).

The above-mentioned test-beds have the following objectives:<ref name="EGNOS V3 SOW"/>
* HIS (High Integrity Service) to develop one system Test Bed (based on SPEED) to engineer and experiment high Integrity (similar to Safety Of Life for multi-modal applications) and authentication (authenticated GEO signal + GEO ranging/UDRE).
* ARCTIC to experiment maritime and aeronautics services in northern latitudes.
* HPS (High Precision Service) to demonstrate and generate interest in an HPS service (with integrity), based on, first GPS and later GPS+GALILEO.
* MLU (MRS Land User service) to investigate, demonstrate and develop new services for Land Users: Proof of Position, Authentication and Emergency Services.

In 2011, two parallel contracts have been commissioned by ESA to perform a Phase A (feasibility) study of EGNOS V3 Phase A. These studies considered different target missions with different levels of consolidation:<ref>EGNOS V3 Mission Guidelines Document, E-RD-SYS-E-0039-ESA, Issue 1.1, 18/01/2011, European Space Agency</ref>

*Consolidated Missions:
** Provide [[GPS General Introduction|GPS]] L1-only augmentation to ensure [[EGNOS Services|EGNOS service]] to legacy users at least until 2030.
** Provide [[GPS General Introduction|GPS]] dual frequency augmentation for LPV-200 service in Europe, Middle-East and Africa.
** Provide [[GPS General Introduction|GPS]] and [[GALILEO General Introduction|GALILEO]] dual frequency augmentation to provide robust (to constellation depletion) LPV-200 service in Europe, Middle-East and Africa.

*Missions to be consolidated:
** Provide [[GPS General Introduction|GPS]] and [[GALILEO General Introduction|GALILEO]] dual frequency augmentation for an enhanced service (lower Vertical Alert Limit than LPV-200) in current [[Wikipedia:European Union|European Union (EU27)]] plus Switzerland and Norway.
** Provide robustness to the loss of one frequency in [[Wikipedia:European Union|EU27]] plus Switzerland and Norway.

Concerning the provision of additional services (i.e.: support to ADS-B, maritime, high precision, land-users…), the objective is that the design will ensure that EGNOS has sufficient in-built expandability and upgradeability capabilities to allow the provision of new products.

==Notes==
<references group="footnotes"/>
==References==
<references/>

[[Category:EGNOS]]
[[Category:EGNOS Future and Evolution]]

EGNOS Signal Structure

2026-04-19T21:39:55Z

Gema.Cueto: Updated reference ICD/SDD links

{{Article Infobox2
|Category=EGNOS
|Editors=GMV
|Level=Basic
|YearOfPublication=2011
|Logo=GMV
|Title={{PAGENAME}}
}}
[[EGNOS General Introduction|EGNOS]] (European Geostationary Navigation Overlay Service) is the European satellite-based augmentation service (SBAS) that complements the existing satellite navigation services provided by the US Global Positioning System (GPS). The EGNOS signal-in-space is broadcast by Geostationary Earth Orbit (GEO) satellites in the L1 frequency, centred at 1575.42 MHz, meeting stringent standards established by organizations like ICAO and RTCA.

The next evolution of EGNOS; namely EGNOS V3, will provide dual-frequency signals on both bands L1 and L5 augmenting both GPS and Galileo constellation data.<ref name="EGNOS V3">[https://www.gsa.europa.eu/newsroom/news/airbus-awarded-egnos-v3-contract EGNOS V3 contract awarded]</ref>

==EGNOS SIS Interface Characteristics==
[[File:EGNOS_Coverage.png|Source: EGNOS Service Notice #22 <ref name= SN 22">[https://egnos-user-support.essp-sas.eu/new_egnos_ops/sites/default/files/documents/service_notice_22_0.pdf EGNOS Service Notice #22] </ref> |340px|thumb|right]]

The EGNOS Signal In Space format is compliant with the ICAO SARPs for SBAS<ref>SARPS Amendment 77, Annex 10 to the Convention on International Civil Aviation, Aeronautical Telecommunications: International Standards and Recommended Practices, Volume 1, Radio Navigation Aids, November 2002.</ref> as stated in the [[EGNOS Open Service | EGNOS Open Service]] Definition Document and the [[EGNOS Safety of Life Service|EGNOS Safety of Life]] Service Definition Document.<ref name=" EGNOS OS SDD">[https://egnos.gsc-europa.eu/sites/default/files/documents/egnos_os_sdd_in_force.pdf?v=1743425975 EGNOS Open Service Definition Document]</ref><ref name=" EGNOS SOL SDD">[https://egnos.gsc-europa.eu/sites/default/files/documents/egnos_sol_sdd_in_force.pdf?v=1726657048 EGNOS Safety of Life Service Definition Document]</ref> The EGNOS SIS interface characteristics comprise carrier and modulation radio frequency, message structure, protocol and content of the EGNOS message (detailed in the [[EGNOS Messages | EGNOS Message Format ]] definition).

EGNOS uses three GEO satellites at different longitude to broadcast its signals across the whole EGNOS service area. See details in the [[EGNOS Space Segment | EGNOS Space Segment]] article. The figure shows the most updated EGNOS GEO satellites coverage with a 5 degrees masking angle.

Contrary to the case of core navigation space vehicles with active navigation payloads, the EGNOS GEO satellites carry transponders relaying the signal transmitted from the [[EGNOS Ground Segment|ground segment]] uplink stations.<ref name=" EGNOS OS SDD"/>

EGNOS V3 will ensure a full continuity of service for the next decade and will be implement the dual frequency and multi constellation world standard, replacing EGNOS V2 which has been in operation since 2011. For this, a new generation of user terminals will be needed according with the new standards for Dual Frequency Multi Constellation (DFMC).<ref name="EGNOS V3">[https://www.gsa.europa.eu/newsroom/news/airbus-awarded-egnos-v3-contract EGNOS V3 contract awarded]</ref>

==EGNOS SIS RF Characteristics==
As any other SBAS, EGNOS broadcasts its augmentation information in L1 band, at 1575.42 MHz, using right-hand circular polarization (RHCP). Each individual second, EGNOS transmit a navigation message containing 250 bits of information.
This raw navigation message is ½ convolutional encoded with Forward Error Correcting (FEC) Code resulting in a 500 symbol/second EGNOS data stream.
This data stream is added modulo-2 to a 1023-bit PRN code, which will then be biphase shift-keyed (BPSK) modulated onto the L1 carrier frequency at a rate of 1.023 Mega-chips/second (Mcps). <ref name=" RTCA MOPS DO 229">Minimum Operational Performance Standards for Global Positioning System/Wide Area Augmentation System Airborne Equipment (RTCA MOPS 229)</ref>

For unobstructed view-lines with elevation angles greater than 5 degrees on the Earth surface, the EGNOS signal is received by 3dBi linearly polarised antennae with a power in the –161 dBW to –153 dBW range, assuming an orientation of the antenna orthogonal to the propagation direction. In addition, spurious transmissions are bounded at least 40dB below unmodulated carrier power.<ref name=" EGNOS OS SDD"/> It is planned to enhance the signal-to-noise ratio in future replenishments of the EGNOS space segment, with the intention to improve the tracking performance at user level.

As stated in MOPS DO 229, the most relevant EGNOS signal characteristics are detailed hereafter:<ref name=" RTCA MOPS DO 229"/>
* '''Carrier Phase Noise''': The phase noise spectral density of the unmodulated carrier is such that a phase locked loop of 10Hz one-sided noise bandwidth is able to track the carrier to an accuracy of 0.1 radians rms.
* '''Signal Spectrum''': The broadcast signal is at GPS L1 frequency of 1575.42 MHz. At least 95% of the broadcast power is contained within a +/- 12MHz band centred at the L1 frequency. The bandwidth of the signal transmitted by an EGNOS satellite is at least 2.2MHz.
* '''Doppler Shift''': The Doppler shift, as perceived by a stationary user, on the signal broadcast by EGNOS GEOs is less than 40 meters per second (≈210 Hz at L1) in the worst case (at the end of life of the GEOs). The Doppler shift is due to the relative motion of the GEO.
* '''Carrier Frequency Stability''': The short term stability of the carrier frequency (square root of the Allan Variance) at the input of the user´s receiver antenna will be better than 5x10-11 over 1 to 10 seconds, excluding the effects of the ionosphere and Doppler.
* '''Polarization''': The broadcast signal is right-handed circularly polarized. The ellipticity will be no worse than 2 dB for the angular range of ±9.1o from boresight.
* '''Correlation Loss''': Correlation loss is defined as the ratio of output powers from a perfect correlator for two cases: 1) the actual receiver EGNOS signal correlated against a perfect unfiltered PN reference, or 2) a perfect unfiltered PN signal normalized to the same total power as the EGNOS signal in case 1, correlated against a perfect unfiltered PN reference. The correlation loss resulting from modulation imperfections and filtering inside the EGNOS satellite payload is less than 1 dB.

==SBAS Signal Generators==
Nowadays, there exists operational commercial off-the-shelf equipment to generate the SBAS signal to be uplinked to the GEO for relay.<ref name=" Novatel GUS-Type 1 Signal Generation Product Sheet ">[http://www.novatel.com/products/gnss-receivers/ground-reference-and-uplink-receivers/gus-signal-generator/ Novatel GUS-Type 1 Signal Generation Product Sheet]</ref>

In addition, there are other flexible platforms useful to generate test signals for development and evaluation of user SBAS receivers.<ref name=" Spirent GSS4100 Signal Generator Product Reference Sheet">[http://www.testequipmentconnection.com/specs/Spirent_GSS4100.PDF Spirent GSS4100 Signal Generator Product Reference Sheet]</ref> These products allow to select specific navigation satellite systems, to define influencing error sources, to choose signal frequency and modulations schemes as well as the RF Front end and filter characteristics.

<references group="footnotes"/>

==References==
<references/>

[[Category:EGNOS|Signal]]
[[Category:EGNOS Signal Structure|Signal]]

EGNOS Services

2026-04-19T21:36:09Z

Gema.Cueto: Updated reference ICD/SDD links

{{Article Infobox2
|Category=EGNOS
|Editors=GMV
|Level=Basic
|YearOfPublication=2011
|Logo=GMV
|Title={{PAGENAME}}
}}
[[EGNOS General Introduction|EGNOS]] (European Geostationary Navigation Overlay Service) is the European Satellite Based Augmentation Service (SBAS) that provides services based on the Global Positioning System ([[GPS Services |GPS]]) signals as well as enhanced accuracy and integrity information. EGNOS currently augments the GPS L1 (1575.42 MHz) Coarse/Acquisition (C/A) civilian signal. EGNOS will augment both GPS and Galileo in the future, using L1 and L5 (1176.45 MHz) frequencies.

EGNOS currently supports three services:<ref>[https://egnos-user-support.essp-sas.eu/new_egnos_ops/egnos-system/about-egnos EGNOS Services]</ref> the [[EGNOS Open Service|Open Service]] (OS), the [[EGNOS Safety of Life Service|Safety of Life Service]] (SoL), and the [[EGNOS Data Access Service (EDAS)|EGNOS Data Access Service (EDAS)]].

==Introduction==
EGNOS supports a wide range of applications through the following Services:
* The [[EGNOS Open Service|EGNOS Open Service (OS)]], freely available to the public in Europe.
* The [[EGNOS Safety of Life Service|EGNOS Safety of Life (SoL) Service]], that provides the most stringent level of signal-in-space performance to all Safety of Life user communities in Europe.
* The [[EGNOS Data Access Service (EDAS)|EGNOS Data Access Service (EDAS)]], for customers who require enhanced performance for commercial and professional use.

<gallery>
Image:egnos_1.png‎
Image:egnos_2.png‎
</gallery>

The service diversity provided by EGNOS supports a wide range of applications, user communities and domains<ref name="EGNOS Applications">[https://www.gsa.europa.eu/egnos/applications EGNOS Applications]</ref>.

==EGNOS Open Service==
[[File:MagicGemini_1.png‎|Accuracy improvement gained with EGNOS Open Service|thumb|right]]

On the 1st October 2009, the European Commission declared that EGNOS' basic navigation signal was operationally ready as an open and free service. In making this announcement, [[EGNOS Open Service]]<ref name="EGNOS Open Service Definition Document">[https://egnos.gsc-europa.eu/sites/default/files/documents/egnos_os_sdd_in_force.pdf?v=1743425975 EGNOS Open Service Definition Document]</ref> started to provide European users with unprecedented positioning precision by improving the accuracy of standalone GPS.

The continuous monitoring of the EGNOS signal shows accuracy gains with respect to GPS within one to two meters and is available more than 99 percent of the time.<ref name="EGNOS Portal">[http://egnos-portal.gsa.europa.eu/ EGNOS Performances Monitoring Portal]</ref>

==EGNOS Safety of Life==
The second key milestone in the EGNOS Programme was the declaration of the [[EGNOS Safety of Life Service|EGNOS SoL Service]]<ref name="SOL DEF">[https://egnos.gsc-europa.eu/sites/default/files/documents/egnos_sol_sdd_in_force.pdf?v=1726657048 EGNOS Safety of Life Service Definition Document]</ref> operational. On the 2nd March 2011, the European Satellite Services Provider (ESSP)<ref name="ESSP">[http://www.essp-sas.eu European Satellite Services Provider]</ref> declared<ref name="SOL DEF"/> the Safety-of-Life (SoL) signal officially available for aviation with the authorization of the European Commission (EC) to provide the service. At this point message type 0 (MT0) that used to transmit the same contents as a regular MT2 message before certification of EGNOS for civil aviation was removed. This service supports, since its announcement, a great number of applications in the transport domain and renders safety-critical operations safer. Moreover, it provides a valuable integrity message to inform the user within six seconds in case of a malfunction of the signal.
The Safety-of-Life service is tailored to safety-critical transport applications in various domains, in particular the service is compliant with the aviation requirementsfor APV-1 and Category I precision approaches. The operational use of the EGNOS SoL service in other domains may require specific authorisation by the relevant authorities in the applications sectors concerned.

The European Union has expressed its commitment to the long term support of EGNOS,<ref name="GSA Web Site">[http://www.gsa.europa.eu/news/europe-officially-launches-egnos-open-and-free-service Europe Officially Launches EGNOS As Open And Free Service]</ref> which will provide services along with Galileo when it becomes operational.

In the same way, the European Commission is planning to extend the coverage of the GEO satellites transmitting the EGNOS signal. While the signal currently covers most European states, it has the built-in capability to extend the coverage area to other regions, such as countries on the EU’s borders and North Africa<ref name="EGNOS for Africa">[https://www.gsa.europa.eu/news/egnos-africa-eu-and-au-join-forces EGNOS for Africa: EU and AU join forces]</ref>. On March 3, 2015 the SAFIR (Satellite navigation services for AFrIcan Region) project officially launched the EGNOS-Africa Joint Programme Office in a ceremony in Dakar, Senegal. SAFIR started on January 15, 2013 and is part of the Africa-EU long-term strategic partnership that aims to enhance safety in air transport. The project covers the set-up, staffing and operations of an EGNOS-Africa Joint Programme Office, and sets up and supports a number of technical working sessions composed of regional stakeholders concerned with GNSS/EGNOS in sub-Saharan Africa.<ref>[http://gpsworld.com/egnos-africa-joint-programme-office-launched/ EGNOS-Africa Joint Programme Office Launched], GPS World, March 18, 2015</ref>.

==EGNOS Data Access Service (EDAS)==
[[File:EDAS_EDAS.jpg|EDAS architecture and services that could be provided through diverse communication channels (Source: EDAS in EGNOS ESSP website <ref name="EDAS in EGNOS ESSP website">[https://egnos-user-support.essp-sas.eu/new_egnos_ops/services/about-edas EDAS in EGNOS ESSP website]</ref>.) |200px|thumb|right]]

Additionally, the provision of EGNOS commercial products as a result of the [[EGNOS Data Access Service (EDAS)|EGNOS Data Access Service (EDAS)]] provides added value to Navigation applications, commercial products and widen the extent of EGNOS applicability to a vast number of environments and purposes.

EDAS is the EGNOS terrestrial data service and offers ground-based access to EGNOS data in real time and also in a historical FTP archive to the authorised users.

EDAS provides the opportunity to deliver EGNOS data to users who cannot always view the EGNOS satellites (such as in urban canyons) or to support a variety of other value added services, applications and research programs. EDAS also permits users to access additional data that is not provided by the EGNOS Signal broadcast by the geostationary satellites. The EGNOS EDAS is available since 26 July 2012 <ref name="EDAS Service Definition document">[https://egnos.gsc-europa.eu/sites/default/files/documents/egnos_edas_sdd_in_force.pdf?v=1734519406 EDAS Service Definition document]</ref>..
In 2006, the European Commission through the GJU (now superseded by the European GNSS Agency, the GSA) commissioned the EDAS system. EDAS allows any authorized entity to plug into EGNOS to receive the internal data collected, generated and delivered by EGNOS for free. Although the idea of providing GNSS data streams in real time is far from being new, EDAS has some key differentiators, the most important one is probably the service reliability. Other benefits that EDAS brings are the high data rate (1Hz), the dissemination of the EGNOS message broadcast by each GEO satellite and the provision of GLONASS raw measurements. Additionally EDAS provides the raw data of the Ranging and Integrity Monitoring Stations (RIMS) and Navigation Land Earth Stations (NLES).
EDAS offers ground-based access to EGNOS data, it is the single point of access for the data collected and generated by the EGNOS infrastructure and it represents the terrestrial commercial data service provided by EGNOS.
More detailed information about EDAS could be found in the EDAS Service Definition document<ref name="EDAS Service Definition document"/>.

==Notes==
<references group="footnotes"/>
==References==
<references/>

[[Category:EGNOS|Services]]
[[Category:EGNOS Services|Services]]

EGNOS Safety of Life Service

2026-04-19T21:27:29Z

Gema.Cueto: Updated reference ICD/SDD links

{{Article Infobox2
|Category=EGNOS
|Editors=GMV
|Level=Basic
|YearOfPublication=2011
|Logo=GMV
|Title={{PAGENAME}}
}}
The EGNOS Safety of Life Service (SoL) consists of an augmentation signal to the Global Positioning System ([[GPS General Introduction|GPS]]) Standard Positioning Service ([[GPS Services |SPS]]) intended for most transport safety critical applications. The target application domains are, thus, aviation, maritime, railway and road where degradation in the navigation system performance without a notice within the specified time to alert would endanger lives.

==Terms and Conditions==
[[File:egnos_4.png|EGNOS SoL certified for civil aviation|300px|thumb|right]]

The Safety of Life Service is accessible to any user equipped with an EGNOS certified receiver and located within the appropriate EGNOS SoL Service area. In general, the EGNOS SoL Service is intended for most
transport applications in different domains where lives could be endangered if the performance of the navigation system is degraded below specific accuracy limits without giving notice in the specified time to alert. This requires that the relevant authority of the particular transport domain determines specific requirements for the navigation service based on the needs of that domain, as well as certification procedures if necessary.

At the date of publication, only the aviation domain has specific service requirements defined in the EGNOS SoL SDD <ref name="SoL">[https://egnos.gsc-europa.eu/sites/default/files/documents/egnos_sol_sdd_in_force.pdf?v=1726657048 EGNOS Safety of Life Service Definition Document]</ref>, as well as certification and individual authorisation procedures developed and implemented.
Therefore, EGNOS SoL Service is tailored for use in aviation, for all phases of flight within the corresponding EGNOS SoL Service area, to aviation users (further “Aviation Users”) namely<ref name="SoL"/>:
* Airspace users, as defined in the Single European Sky (SES) Regulation, equipped with an EGNOS certified receiver and located within the appropriate EGNOS SoL Service area corresponding to the phase of flight in which this service is used.
* Organisations implementing EGNOS based procedures responsible for the operational use of the respective procedure:
** Air Navigation Service Providers (ANSP)
** Aerodrome Operators
** Rotorcraft Operators
** Any other organisation upon its competent authority approval.

For some of these organisations, the signature of an EGNOS Working Agreement (EWA) with the EGNOS Provider is required.

Navigation operations based on the EGNOS SoL Service may require authorisation issued by the relevant authority unless the specific authority or applicable regulation states that no such authorisation is required. This authorisation, as defined in EGNOS Safety Of Life Service Definition Document <ref name="SoL"/>, is subject to specified operational conditions and limitations, existence of published navigation procedure and to the certification of the on board navigation equipment.

Consequently, an aircraft or operator will need to be subscriber of the required Service Level Agreement in order to get a service guarantee from the EGNOS Service Provider on the EGNOS Safety of Life Service. In addition, the service guarantee will only be applicable within the Safety of Life Service area.

==EGNOS SoL for Aviation==
[[File:EGNOS_equipped_Aircraft.jpg‎|EGNOS-equipped cockpit|300px|thumb|right]]

The SoL Service is intended to support a wide range of transport domains. Nevertheless, the main objective of the EGNOS SoL service is to support civil aviation operations down to Localizer Performance with Vertical guidance (LPV). This means that the service is compliant with aviation Approach with Vertical Guidance (APV-I) requirements defined in the International Civil Aviation Organization (ICAO) Standard and Recommended Practices (SARPs) for SBAS<ref name="ICAO">ICAO Annex10 Volume I (Radio Navigation Aids) – 6th Edition – July 2006 amendment 85</ref> as expressed in EGNOS Safety of Life Service Definition Document.<ref name="SoL"/>

Using GNSS positioning technology LPV-200 delivers accurate information on an aircraft’s approach to a runway. Lateral and angular vertical guidance is resulting without the need for visual contact with the ground until an aircraft is 200 feet above the runway.
LPV-200 is very important in the EGNOS development because it is providing GPS augmentation in Europe, and it is free and does not requires to upgrade to an airport's ground infrastructure or to the EGNOS certified receivers.<ref name="LPV 200">[https://www.gsa.europa.eu/news/egnos-lpv-200-enables-safer-aircraft-landings EGNOS LPV 200 Enables Safer Aircraft Landings]</ref>

At the time of the edition of this article, only the aviation domain has specific service requirements, as well as certification and individual authorization procedures developed and implemented.

On the 2nd March 2011, the EGNOS Service Provider (ESSP)<ref name="ESSP">[http://www.essp-sas.eu European Satellite Services Provider]</ref> declared<ref name="SoL"/> the Safety-of-Life (SoL) signal officially available for aviation with the authorization of the European Commission (EC) to provide the service. At this point message type 0 (MT0) that used to transmit the same contents as a regular MT2 message before certification of EGNOS for civil aviation was removed.

The aviation user, as mentioned in the [[#Terms and Conditions|Terms and Conditions]] definition, is subject to the specific Working Agreements between ESSP and Air Navigation Service Providers (ANSPs) as stated by the EC Single European Sky regulation.<ref name="Minimum Operational Performance Standards for Global Positioning System/Wide Area Augmentation System Airborne Equipment"</ref> EC Single European Sky regulation "> Regulation (EC) No 549/2004 of the European Parliament and of the Council of 10 March 2004 laying down the framework for the creation of the single European sky</ref>

The EGNOS SoL Service will be provided for a minimum period of 20 years and any significant change in the service will be notified at least six years in advance.'

==EGNOS Safety of Life Receivers==

The reference SBAS receiver standards have also been developed by the civil aviation community. These standards are called SBAS Minimum Operational Performance Standards (MOPS) and are published by the Radio Technical Commission for Aeronautics (RTCA) under the reference DO-229.<ref>Minimum Operational Performance Standards for Global Positioning System/Wide Area Augmentation System Airborne Equipment</ref>This receiver standard has been designed by and for the aviation community and therefore supports both horizontal and vertical navigation and implements a large number of features aimed at ensuring the integrity of the derived position.

This standard identifies different classes of user receivers depending on the intended operations. The main characteristics of the EGNOS equipment operational classes are shown in the following table.

{| class="wikitable"
|-
!|Operational Class||Phase of flight
|-
| Class 1
| Oceanic and domestic in route, terminal, approach (LNAV), and departure operation.
|-
| Class 2
| Oceanic and domestic in route, terminal, approach (LNAV, LNAV/VNAV), and departure operation.
|-
| Class 3
| Oceanic and domestic in route, terminal, approach (LNAV, LNAV/VNAV, LP, LPV), and departure operation.
|-
| Class 4
| Equipment that supports only the final approach segment operation
|}

For EGNOS, the minimum performance levels assume equipage with a class 1 receiver (for NPA service level) or class 3 receiver (for APV-I and LPV-200 service levels) under the conditions in terms of number of satellites in view for a fault free receiver.

For non-aviation SoL users, alternative EGNOS message processing may be implemented, deviating from the DO-229 MOPS standard. However, the EGNOS system performance has not been characterised for such a receiver configuration and therefore the performance experienced by such receivers is likely to deviate from that described in the EGNOS SoL Service Definition Document.

==Safety of Life Performance==
[[File:EGNOS_SOL.PNG‎|Reference map for APV-I at 99%. Source: EGNOS SoL SDD <ref name="SoL"/>|600px|thumb|right]]

The EGNOS system has been designed to support different types of civil aviation operations according to the SoL service performance requirements issued by ICAO.. The EGNOS SoL Service performance values are: <ref name="SoL"/>

{| class="wikitable"
|-
! rowspan="2" | Service
! colspan="2" | [[Accuracy]] (95%)
! colspan="4" | [[Integrity]]
! rowspan="2" colspan ="2" | [[Continuity]]
! rowspan="2" | [[Availability]]
|-
! Lateral
! Vertical
! Integrity
! colspan="3" | TTA
|-
! [[EGNOS Safety of Life Service|NPA]]
| align="center" | 220m
| align="center" | -
| align="center" colspan="3" | 1 – 1x10⁻⁷/h
| align="center" | Less than 6 seconds
| align="center" | <1 – 1x10⁻³ per hour in most of ECAC || <1 – 2.5x10⁻³ per hour in other areas of ECAC
| align="center" | 0.999 in all ECAC
|-
! [[EGNOS Safety of Life Service|APV-I & LPV200*]]
| align="center" | 3m
| align="center" | 4m
| align="center" colspan="3" | 1 – 2x10⁻⁷/approach
| align="center" | Less than 6 seconds
| colspan="1" align="center" | <1 – 1x10⁻⁴ per 15 seconds in the core of ECAC || 1 –5x10⁻⁴ per 15 seconds in most of ECAC landmasses
| align="center" | 0.99 in most of ECAC landmasses
|-
! *Comment
| colspan = "2" | Accuracy values at given locations are available at:https://egnos-user-support.essp-sas.eu/new_egnos_ops/
For LPV-200 new accuracy requirements imposed by ICAO Annex 10 ([RD-1]) see section 6.3.3.2
| align="center" colspan = "4"| N/A
| align="center" colspan = "3" | See sections 6.3.1.3, 6.3.2.4 and 6.3.3.4 for detailed availability maps <ref name="SoL"/>
See sections 6.3.1.4, 6.3.2.5 and 6.3.3.5 for detailed continuity maps <ref name="SoL"/>
|}

==Benefits for Civil Aviation==
[[File:ATR42_trial.jpg|ATR42 landing trials using EGNOS|300px|thumb|right]]

The EGNOS Safety of Life service was declared operational for use in aviation upon completion of a certification process against applicable Safety of Life standards and requirements. In particular for civil aviation, Single European Sky regulations were applied.

This declaration enables precision approaches and renders air navigation safer. In the same way, this accessible Service contributes to reducing delays, diversions and cancellations of flights while the airport capacities are increased and operating costs reduced.

Some of the most remarkable advantages provided by the EGNOS Safety of Life service were enumerated in the EGNOS Safety of Life press release published in the European Commission EGNOS homepage:<ref name="EC EGNOS Portal">[https://ec.europa.eu/growth/sectors/space/egnos_en European Commission EGNOS homepage]</ref>
*'''Increased aviation safety''': EGNOS allows to perform precision approaches which reduce safety risks considerably.
*'''Lower operating costs''': EGNOS signals are freely accessible and only requires a receiver aboard the aircraft with no necessity of ground infrastructure.
*'''Lower CO2 emissions''': EGNOS permits more efficient definition of flight routes.
*'''Less delays, diversions and cancellations''': EGNOS allows lower aircraft separation distances which results in fewer delays, diversions and cancellations of flights.
*'''Less noise pollution''': EGNOS facilitates optimized flight routes and 'curved approach' procedures allowing planes to commence their descent closer to the runway.
*'''Increased capacity for smaller airports''': The vertical guidance offered by EGNOS means planes are able to land in restricted visibility conditions, increasing the capacity of airports.

The second generation of the European Geostationary Navigation Overlay Service, EGNOS V3, which is planned to enter service in 2025, will take advantage of in-operation Galileo signals, as well as new frequencies from an improved class of GPS satellites. Use of the L5 second frequency will improve service robustness against errors and propagation delays caused by the ionosphere. This new EGNOS version implies benefits for aircraft. EGNOS V3 will be able to guide the latest avionics accurately and safely down to Category 1 (VLA = 10m), while also providing legacy users equipped with current avionics a more robust version of the current LPV200, or 35 m vertical limit for vertical guidance service. <ref name="ESA NT">[https://www.esa.int/Applications/Navigation/New_technology_version_of_EGNOS_will_harness_Galileo_for_aviation New technology version of EGNOS will harness Galileo for aviation, ESA website] </ref>

==Notes==
<references group="footnotes"/>
==References==
<references/>

[[Category:EGNOS|Safety]]
[[Category:EGNOS Services|Safety]]

EGNOS Open Service

2026-04-19T21:20:42Z

Gema.Cueto: Updated reference ICD/SDD links

{{Article Infobox2
|Category=EGNOS
|Editors=GMV
|Level=Basic
|YearOfPublication=2011
|Logo=GMV
|Title={{PAGENAME}}
}}
The EGNOS Open Service consists of a set of signals for timing and positioning intended for general purpose applications. It is fully accessible by means of a GNSS/SBAS compatible receiver, it is free of charge and it does not require any receiver specific certification nor authorization.

==Introduction==
[[File:egnos_3.png|The EGNOS Open Service was declared available in October 2009|200px|thumb|right]]

The EGNOS Open Service is fully operational and the signal-in-space is available since October 2009 for any user equipped with an EGNOS enabled receiver without any further requirement. Details about the EGNOS-enabled receiver design specifications can be found in EGNOS Open Service - Service Definition document.<ref name="EGNOS Open Service specifications">[https://egnos.gsc-europa.eu/sites/default/files/documents/egnos_os_sdd_in_force.pdf?v=1743425975 Applicable EGNOS Open Service – Service Definition Document (EGNOS OS-SDD)]</ref>

This service is provided through the GEO satellites within the EGNOS service area and it improves GPS performances in Europe. However, EGNOS OS shall only be used for non-safety critical purposes, i.e. those where degraded performances could not provoke direct or indirect personal damage. Besides, no service guarantee or liability is provided by the EGNOS Service provider,<ref name="ESSP Web Site">[http://www.essp-sas.eu/ ESSP Web Site]</ref> the European Union, the European GNSS Agency (GSA)<ref name="GSA Web Site">[https://www.gsa.europa.eu/ GSA Website]</ref> or the European Space Agency (ESA).<ref name="ESA EGNOS Portal">[http://www.esa.int/esaNA/egnos.html European Space Agency EGNOS Portal]</ref>

[[File:tour_de_france_EGNOS.jpg|Lance Armstrong´s arrival at the Summit of l'Alpe d´Huez where riders were tracked with EGNOS|200px|thumb|right]]

The EGNOS Open Service is the first EGNOS service to become available and its main objective is to obtain enhanced positioning accuracy by correcting the error contributions that affect GPS signals, which are related to satellite clocks, satellite payload induced signal distortion, satellite position uncertainties and ionospheric delays whereas other effects, such as tropospheric delays, multipath or user receiver contributions, are local effects and cannot be corrected by an [[SBAS General Introduction|SBAS]] system.

The EGNOS OS Definition Document states that the service is ''available to any user equipped with a SBAS enabled receiver.''<ref name="EGNOS Open Service specifications"/>
The OS was declared available on the 1st October 2009<ref name="EGNOS Open Service specifications"/> and this EGNOS service is intended to be provided for a minimum period of 20 years with a 6 years in advance notice in case of significant changes in the Services provided.

==Performance requirements==
[[EGNOS Performances|EGNOS performances]] are considered from a user perspective and they are expressed in terms of availability, continuity, integrity and accuracy. The minimum requirements for these terms are defined by SBAS standards which were conceived for civil aviation applications. These standards are called SBAS Minimum Operational Performance Standards and are published by [http://www.rtca.org/ RTCA] under the reference DO-229.<ref name="EGNOS Open Service specifications"/> <ref name=" RTCA MOPS DO 229">Minimum Operational Performance Standards for Global Positioning System/Wide Area Augmentation System Airbone Equipment (RTCA MOPS DO-229)</ref>

Consequently, MOPS intends to support aviation use and provides a series of features to guarantee integrity which, as expressed in EGNOS OS Service Definition Document,<ref name="EGNOS Open Service specifications"/>''may result in degraded performance over what could be reached if implementing a tailored processing of EGNOS signals for OS,'' due to the stringent aviation requirements.

[[File:EGNOS OS.png|EGNOS OS Compliance Area (From EGNOS OS-SDD)<ref name="EGNOS Open Service specifications"/>|200px|thumb|right]]

Typically, all SBAS receivers designed to support OS shall:<ref name="EGNOS Open Service specifications"/>
*''Use the Geostationary satellite ranging function if available (broadcast through message types 9 and 17, this function is currently not supported by EGNOS).
*''Decode and apply satellite clock corrections (broadcast through message types 2-5 and corresponding to satellites selected by message type 1).''
*''Decode and apply satellite ephemeris corrections (broadcast through message types 24- 25).''
*''Decode and apply ionospheric corrections (broadcast through message type 26 for ionospheric grid points selected by message type 18).''
*''Take into account major warnings sent through the SBAS messages (broadcast through message types 2-5 and 6).''

''Additionally, an OS receiver may use the content of message type 12, if used for time determination.''

In order to define OS user performances, a number of assumptions are made:
*The user receiver shall implement MOPS DO-229 navigation weighted solution and message processing (equivalent to Class 3) but does not take into consideration the protection level criteria to declare that a solution is available.
*The EGNOS receiver shall take into account the monitoring of satellites and Ionospheric Grid Points according to the UDRE/GIVE indicators as a MOPS receiver Class 3.
*A clear sky environment is assumed with no obstacles masking satellite visibility greater than 5° above the local horizontal plane.

The minimum level of performance against which the system has been designed, as well as data of actual performance, is provided in the table and map below.<ref name="EGNOS Open Service specifications"/>
This information is solely presented for transparency in order to enable the user to make an informed decision regarding EGNOS OS use and, thus, actual EGNOS OS performance may differ in the future.

{| class="wikitable"
|-
!| ||Definition || Value
|-
|'''Horizontal [[Accuracy]]'''||Corresponds to a 95% confidence bound of the bi-dimensional position error in the horizontal local plane for the worst user location.||3 m
|-
|'''Vertical [[Accuracy]]'''||Corresponds to a 95% confidence bound of the uni-dimensional unsigned position error in the local vertical axis for the worst user location.||4 m
|}

==Limitations==
The minimum performance levels stated in Section [[#Performance Requirements| Performance Requirements]] are fulfilled in the vast majority of cases and service availability is also provided. However, there might be some situations where non nominal navigation performances are obtained.
The most common causes of abnormal EGNOS behavior and their impact on performances are listed in the following table:<ref name="EGNOS Open Service specifications"/>

{| class="wikitable"
|-
!|'''Cause of Service Degradation'''||'''Impact on OS User'''
|-
| '''Broadcasting delays''':Acquisition of all SBAS parameters make take up to 5 minutes. || EGNOS Service is not available until a few minutes after receiver connection.
|-
| '''GPS or EGNOS Signal attenuation''': Adverse weather conditions, using satellite navigation user heavy foliage and indoor environments weaken signals and may provoke loss of lock or degraded performance. || Degraded Position accuracy
|-
| '''EGNOS Signal Blockage''': For users in high latitudes geostationary satellites may fall below the visibility mask whereas in urban environments the EGNOS signal could be lost for a period of time.|| Performance degradation after a period of time: EGNOS will cope with temporary signal blockages but corrections will not be valid after a certain period.
|-
| '''Local Multipath''': Signals suffer reflections on nearby objects causing local errors on the measurements which cannot be corrected by the EGNOS system due to their local nature. ||Degraded position accuracy, especially on static or slowly moving users.
|-
| '''Signal Interference''': Transmissions on adjacent frequency bands may interfere GNSS and EGNOS signals.|| It may result in accuracy degradation or total navigation loss depending on the intensity of the interference.
|-
| '''Ionospheric Scintillation''': Ionospheric disturbances due to the solar activity can lead to severe signal degradation or even signal lost.||Satellite monitoring and the Navigation solution will be degraded.
|-
| '''Receiver Design''': Before the certification of EGNOS for civil aviation, EGNOS used to transmit message MT0 with the contents of a regular MT2 which could be processed by a non-SoL receiver.||The removal of MT0 upon certification of the EGNOS Safety of Life Service, could cause the OS to be denied or a suboptimal performance obtained depending on the receiver manufacturer and configuration used.
|-
| '''Degraded GPS core constellation:''': GPS constellation becomes temporarily depleted and that it does not meet the GPS SPS PS commitment.|| EGNOS performance may be degraded, even worse than the minimum performance stated in EGNOS OS SDD.
|}

==Credits==
The information provided in this article has been compiled by GMV. In some cases, tables and paragraphs have been extracted from the indicated references, in particular from the ''EGNOS OS Definition Document.''<ref name="EGNOS Open Service specifications"/>
<references group="footnotes"/>

==References==
<references/>

[[Category:EGNOS|Open]]
[[Category:EGNOS Services|Open]]

EGNOS Data Access Service (EDAS)

2026-04-19T21:13:31Z

Gema.Cueto: Updated reference ICD/SDD links

{{Article Infobox2
|Category=EGNOS
|Editors=GMV
|Level=Basic
|YearOfPublication=2011
|Logo=GMV
|Title={{PAGENAME}}
}}
EDAS is the technical core of the EGNOS Commercial Data Distribution Service (CDDS) and provides the opportunity to deliver EGNOS data to users who cannot always view the EGNOS satellites (such as in urban canyons) or to support a variety of other value added services, applications and research programs.<ref name=" EDAS Beta test findings">The EGNOS Service to Provide Ground Based Access to EGNOS – EDAS Beta test findings; Reinhard Blasi, GSA; Rafael Cardoso-Herce, Didier De Greef, ESSP; José Ramón López-Pérez, Francisco J. Jiménez-Roncero, AENA; Ángel Gavín-Alarcón, GMV; Monica Pesce, VVA; Proceedings of the 23rd International Technical Meeting of The Satellite Division of the Institute of Navigation (ION GNSS 2010), Portland, OR, September 2010</ref>

In 2006, the European Commission through the GJU (now superseded by the European GNSS Agency, the [http://www.gsa.europa.eu GSA]) commissioned the EDAS system. EDAS allows any registered entity to plug into EGNOS to receive the internal data collected, generated and delivered by EGNOS for free. Although the idea of providing GNSS data streams in real time is far from being new, EDAS has some key differentiators, the most important one is probably the service reliability. Other benefits that EDAS brings are the high data rate (1Hz), the dissemination of the EGNOS message broadcast by each GEO satellite and the provision of GLONASS raw measurements. Additionally EDAS provides the raw data of the Ranging and Integrity Monitoring Stations (RIMS) and Navigation Land Earth Stations (NLES).<ref name=" EDAS Beta test findings"/>

EDAS provides ground-based access to EGNOS data, through a collection of services, which are accessible to registered users through the Internet and are oriented to users in different domains of application such as Location Based Services (LBS), a broad range of services in professional GNSS markets, Assisted-GNSS (A-GNSS) concepts, and related R&D activities.<ref name="EGNOS EDAS SDD">[https://egnos.gsc-europa.eu/sites/default/files/documents/egnos_edas_sdd_in_force.pdf?v=1734519406 EGNOS EDAS SDD]</ref>

In fact, EDAS to users the possibility to access the EGNOS data even when the Signal In Space (SIS) is not available due to lack of visibility of the satellites (Urban Canyon, Indoor, ...).
EDAS was officialy declared available on July 2012. The last release of the Service Definition Document (SDD) is available [https://egnos.gsc-europa.eu/sites/default/files/documents/egnos_edas_sdd_in_force.pdf?v=1734519406 here].

Since April 2013, four new EDAS Services have been introduced: Data Filtering, FTP, SISNET and NTRIP.<ref name=" EDAS Services">[https://egnos-user-support.essp-sas.eu/new_egnos_ops/ EDAS Services]</ref>

==EDAS Overview ==
The main purpose of EDAS is to provide a basis for new applications beyond those from the nominal EGNOS Open Service and Safety of Life Service. To do so, the objective is to provide an interface point where multiple EGNOS Multimodal Service Providers can obtain the EGNOS products in real-time and within guaranteed delay, security, safety and performance boundaries and also in a historical FTP archive to authorised users. Actually there exists the possibility of binding and long-term service agreements.
As a result EGNOS information broadcast through the GEO Signal In Space (SIS) becomes accessible, as well as the EGNOS Ranging, Integrity and Monitoring Stations (RIMS) raw data.
EDAS delivers three main types of data in real-time and historic GNSS, via ground transmission systems:
# EGNOS augmentation messages, also transmitted by EGNOS geostationary satellites.
# Raw GPS (L1 and L2), GLONASS L1 and EGNOS L1 geostationary satellites observations and navigation data collected by the entire network of Ranging and Integrity Monitoring Stations (RIMS) and Navigation Land Earth Stations (NLES).
# Differential GNSS (DGNSS) corrections and RTK (RealTime Kinematic) messages for the EGNOS stations allowing users implementing advanced positioning techniques.

==EDAS Services ==
EDAS is not an end-user product. The data streams can be used by Service Providers to generate added value to the final customers by improving the availability and accuracy of the positioning. For instance, one may think of a Service Provider that takes the EGNOS message from EDAS and disseminates it to its customers through the Internet or GPRS.

The EDAS services are classified as Main Data Stream services (Service Level 0, Service Level 1, and Service Level 2) and Added Value Services (Data Filtering, FTP, SISNet and Ntrip).<ref name="EGNOS EDAS SDD"/>

The main types of data provided by the main data stream Services are:<ref name=" EDAS Services"/>
* Service Level 0 (SL0): it provides data encoded in ASN.1 format. It is recommended for those users willing to transmit data in raw format, or transmit them in a format that allows a complete reconstruction after decoding.
* Service Level 2 (SL2): it is used to transmit data in RTCM 3.1 standard. It includes data from Service Level 1 (decommissioned on 1st July 2014) and an EDAS property message (RTCM Message Number 4085) with additional information (i.e. RIMS status, RIMS APC data, ionospheric and UTC data, etc.).

Appart from the Main Data Stream Services, there are others that provide added value such as:

* [[SISNET |EDAS SiSNet Service]]:
This service will provide the EGNOS messages in real time using a [[SISNET|SISNeT]] protocol defined by ESA. Since the information is sent by means of an open standard protocol, the users can develop their own application and select which data to retrieve.
The full description of this protocol can be found [http://www.egnos-pro.esa.int/Publications/SISNET/SISNET_UID_3_1.pdf here].

Specific guidelines for the access and usage of the EDAS SISNeT service (EDAS SISNeT – User Information Package) are available at the EDAS specific section of the [http://egnos-user-support.essp-sas.eu/ EGNOS User Support Website].

*EDAS FTP service:
This service provides to the EDAS users EDAS/EGNOS historical data in different formats and data rates. The user is able to access this service through a normal FTP client.
Specific guidelines for the access and usage of the EDAS FTP service, including naming conventions and folder structure (EDAS FTP-User Information Package), are available at the EDAS specific section of the [http://egnos-user-support.essp-sas.eu/ EGNOS User Support Website].

[[File:EDAS_FTP.png | EDAS FTP service<ref name="EGNOS EDAS SDD"/>|380px|thumb|centre]]

*EDAS NTRIP Service:

The EDAS-based NTRIP service provides GNSS data (RTCM format) coming from the EGNOS network through the Ntrip protocol in real-time. In fact, EDAS disseminates GNSS data in RTCM 2.1, 2.3 and 3.1. Differential GNSS corrections and phase measurements, as well as additional messages for RTK (real-time kinematic) implementation, are provided within the NTRIP data.
NTRIP is an RTCM standard designed for disseminating differential correction data (e.g. in the RTCM-104 format) or other kinds of GNSS streaming data to stationary or mobile users over the Internet, allowing simultaneous PC, laptop, PDA, or receiver connections to a broadcasting host. NTRIP supports wireless Internet access through Mobile IP Networks like GSM, GPRS, EDGE, or UMTS.(EDAS Ntrip – User Information Package) are available at the EDAS specific section of the [http://egnos-user-support.essp-sas.eu/ EGNOS User Support Website].

[[File:EDAS Ntrip.png | EDAS Ntrip Message Types <ref name="EGNOS EDAS SDD"/>|380px|thumb|centre]]

*EDAS Data Filtering Service:

This service allows EDAS users to access a subset of the Service Level 0 or Service Level 2 data(hence the data are available in ASN1 and RTCM 3.1 formats respectively). The upgraded 2.0 version of the EDAS Client SW makes it possible to select one of the available predefined groups, which are a subset of the EGNOS stations, and the data rate of the received messages.
This means that EDAS users can subscribe to a predefined group of RIMS and retrieve data from these sets of stations at 1Hz or 1/30 Hz, thereby reducing the bandwidth consumption and amount of data to be processed on the user side. The list of available groups and information on how to access this EDAS Service can be found in the EDAS Client SW User Manual.
Specific guidelines for the access and usage of the EDAS SISNeT service (EDAS SISNeT – User Information Package) are available at the EDAS specific section of the [http://egnos-user-support.essp-sas.eu/ EGNOS User Support Website].

==EDAS Architecture ==
[[File:EDAS_Architecture.png | EDAS high level architecture<ref name="EGNOS EDAS SDD"/>|380px|thumb|left]]

The EDAS architecture is composed of the following elements:
EDAS Client Software (CS): represents the functional interface between the EGNOS Data Server (EDS) and the Service Provider (SP) and it provides authentication, data communication and quota and integrity management
EGNOS Data Server: transforms data received from INSPIRE (a dedicated interface to access to EGNOS data) from the EGNOS proprietary format to ASN.1 (SL0) and RTCM (SL1). For each message received EDS creates one or more RTCM messages and one ASN.1 message. In addition it delivers information to the CS about the status of the messages quota contracted by the SP.

The EDAS architecture is decomposed into two separate elements<ref name="EGNOS EDAS SDD"/>:

-EDAS system, implementing the interface with the EGNOS infrastructure and performing the necessary data processing to provide the different EDAS Services through Internet. Users can connect directly to EDAS system for some of the services which are based on standard protocols (FTP, SISNET and NTRIP).

-The EDAS Client SW, resident at user level, implementing the external interface of some of the EDAS services (EDAS Service Level 0, Service Level 2 and EDAS Data Filtering Service). The EDAS Client SW is responsible for basic security functions and for the interface with the EDAS system through the appropriate communication means.

[[File:EDAS_diagram.png| EDAS Services Diagram<ref name="EGNOS EDAS SDD"/>|380px|thumb|left]]

The EDAS Client SW is a platform-independent interface element allowing the connection of Users to EDAS system for reception of Main Data Streams. This tool is only available after registration and users make use of it to obtain the EGNOS products in real-time from the EDAS system, then perform the necessary processing and finally provide services to end users via non-GEO means.
Moreover, it is in charge of handling the connection between users and EDAS for the Main Data Streams and the Data Filtering Services, through a specific protocol (internal to EDAS and not available to the general public).

EDAS also contains a Man Machine Interface (MMI) for daily operations, monitoring and control. All the elements (but the operator MMI) have redundancy in order to have high availability in the system. On top of that, security is an issue due to the fact that EDAS is connected to the heart of the EGNOS system and, in order to face it, EDAS has been protected and audited against intentional and unintentional attacks.<ref name=" EDAS Beta test findings"/>

EDAS users and/or application Providers will be able to connect to EDAS, and directly exploit the EGNOS products or offer added-value services based on EDAS data to final customers.

==EDAS Performance==
This section presents the EDAS Services performance in terms of availability and latency:
* Availability: percentage of the time in which an EDAS service is delivering data according to specifications. The availability of EDAS services is measured at the EDAS system output (excluding external network performance).<ref name="EGNOS EDAS SDD"/>
* Latency: time elapsed since the transmission of the last bit of the navigation message from the space segment (EGNOS and GPS/GLONASS satellites) until data leave the EDAS system (formatted according to the corresponding service level specification). EDAS latency is a one way parameter defined for real-time services.<ref name="EGNOS EDAS SDD"/>

===EDAS Services Availability===

The following table provides the minimum monthly availability of the EDAS services.

{| class="wikitable" align="center"
|+align="bottom" |''EDAS Services Availability''
|-
!
! SL0
! SL2
! SISNet
! FTP
! Data Filtering
! Ntrip
|- align="center"
| EDAS Services Availability
| 98.5%
| 98.5%
| 98%
| 98%
| 98%
| 98%
|- align="center"
|}

It should be noted that EDAS service availability performance is nominally higher than the above figures.

===EDAS Services Latency===

The following table provides the maximum monthly latency (percentile 95) of the EDAS services.

{| class="wikitable" align="center"
|+align="bottom" |''EDAS Services Latency''
|-
! rowspan="2" |
! rowspan="2" | SL0
! rowspan="2" | SL2
! rowspan="2" | SISNet
! rowspan="2" | FTP
! rowspan="2" | Ntrip
! colspan="2"| Data Filtering
|- align="center"
! SL0
! SL2
|- align="center"
| EDAS Services Latency
| 1.3 s
| 1.450 s
| 1.150 s
| N/A
| 1.75 s
| 1.6 s
| 1.75 s
|- align="center"
|}

It should be highlighted that EDAS services latency performance is nominally lower than the above figures.

==EDAS Connections ==
[[File:EDAS_application.JPG | EDAS Data Access. |300px|thumb|right]]

Access to the EDAS data is possible by one of the two following means:<ref name=" EDAS Connection">[http://www.gsa.europa.eu/egnos/edas/how-do-i-access-edas EDAS Connection]</ref>
* Internet connection allowing full transmission of all data on best-effort basis (no latency and data integrity guarantee).
* Higher performance point-to-point (PTP) direct link to the EDAS Server.

The standard and easiest way to receive EDAS is over the internet. Simply by downloading the client software, EDAS can be received through a typical broadband internet connection, where:
* ASN.1 format service requires 600kb/s.
* RTCM format service requires 300kb/s.
* Both formats can be received at 900kb/s.

It is possible to obtain a dedicated faster connection. This might require a fixed line solution providing a dedicated line for each user. The costs for introducing the fixed line solution to EDAS need to be covered by the user, but assistance and support in setting up the connection is provided.

==EDAS Based Applications ==
Given the potential of the architecture deployed by EDAS, the diversity of data provided and its suitability for a wide range of environments and domains, it offers multiple opportunities for harnessing EDAS to provide applications and services,<ref name=" EDAS Applications">[http://www.gsa.europa.eu/egnos/edas/applications EDAS Applications]</ref> specially for Redistribution of EGNOS augmentation messages and professional GNSS Services.

EDAS has proved to play a role within the identified market segments considered in the [[EGNOS Commercial Data Distribution Service| EGNOS CDDS]]. There is a continuously growing EDAS user community and there are a wide range of applications that provide EDAS-based services that comprise the [[EGNOS Commercial Data Distribution Service| CDDS]].
Furthermore, the EDAS-N project examined how the current EGNOS Data Access Service (EDAS) should evolve to meet user needs between 2020 and 2030. On the basis of its analysis, it proposes 8 new EDAS services.
As EDAS is expected to disseminate EGNOS V3 data over this period, the analysis focuses on what additional features could help generate new EDAS services for users and service providers.
The EDAS-N project defined how the current EGNOS EDAS should evolve to meet more demanding user needs between 2020 and 2030. The analysis looked at potential new EDAS services and their market uptake. It also estimated their capital expenditure and operating expense. The project proposed a final set of 8 new EDAS-based services, and defined their implementation schedule.
The uptake of the next generation of EDAS is estimated at 178 direct users (mainly service providers) and 350,000 indirect users by 2030. <ref name=" EGNOS data access service">[https://www.gsa.europa.eu/egnos-data-access-service EGNOS Data Access Service]</ref>

==Notes==
<references group="footnotes"/>
==References==
<references/>

[[Category:EGNOS]]
[[Category:EGNOS Services]]

EGNOS Commercial Data Distribution Service

2026-04-19T21:05:05Z

Gema.Cueto: Updated reference ICD/SDD links

{{Article Infobox2
|Category=EGNOS
|Editors=GMV
|Level=Basic
|YearOfPublication=2011
|Logo=GMV
|Title={{PAGENAME}}
}}
The EGNOS Commercial Data Distribution Service (CDDS) represents the provision of additional data for professional users not provided by the EGNOS signal broadcast by geostationary satellites but by other distribution channels. This service is currently provided through the [[EGNOS Data Access System (EDAS) | EGNOS Data Access System (EDAS)]].

==First step towards EGNOS CDDS: EGNOS Data Access System (EDAS)==
The [[EGNOS Data Access System (EDAS) | EGNOS Data Access System (EDAS)]], provides the following services:<ref name=" Introduction to EDAS">[http://www.gsa.europa.eu/egnos/edas GSA's Introduction to EDAS]</ref><ref name=" SDD">[https://egnos.gsc-europa.eu/sites/default/files/documents/egnos_edas_sdd_in_force.pdf?v=1734519406 EGNOS EDAS Service Definition Document]</ref>
*Transmission of EGNOS data using the RTCM SC 104 standard (directly usable by maritime DGPS receivers).
*Access to raw data from the RIMS network receivers.
*Differential GNSS (DGNSS) corrections and [[Real Time Kinematics |RTK (RealTime Kinematic)]] messages for the EGNOS stations allowing users implementing advanced positioning techniques.

EDAS constitutes the means for the EGNOS multimodal service growth. It represents the main interface point for multimodal Service Providers in order to deliver EGNOS products in real-time, within guaranteed performance boundaries.<ref name=" The vehicle to the future EGNOS CDDS">[http://www.egnos-pro.esa.int/Publications/NAVITEC%202008/EDAS_THE_VEHICLE_TO_FUTURE_EGNOS_CDDS.pdf The vehicle to the future EGNOS CDDS]</ref>

EDAS service has been provided in beta phase since 2009 and was officially declared available to EU users by the EC on 26 July 2012. The European Satellite Service Provider (ESSP)was the single point of access for the data collected and generated by the EGNOS infrastructure and it represents an intermediate step towards the definition of the EGNOS CDDS by the European Commission.<ref name=" ESSP Web Site">[http://www.essp-sas.eu/news/ ESSP Web Site]</ref>

==EGNOS CDDS Applications==
Service providers can exploit the CDDS to provide added value to final users in various domains and applications such as the ones highlighted<ref name=" EGNOS Applications">[https://www.gsa.europa.eu/gnss-applications/segment-pages EGNOS Applications]</ref>:
*Applications for individual handsets and mobile phones (LBS)
*Road transport
*Maritime & Rail transport
*Civil protection and Goods Transportation
*Agriculture
*Aviation
*Timing and synchronization
*Mapping and Surveying

There are a series of pioneer R&D projects in the aforementioned domains that make use of EGNOS through EDAS. Some of them are detailed hereafter:
===Location Based Services (LBS)===

[[File:LBS_SARFOS_picture.JPG| EGNOS EDAS : LBS Application |250px|thumb|right]]

The LBS sector include GNSS-enabled mobile phones, smartphones and services, and represents an important part of the global GNSS market.<ref name="Market Report">[https://www.gsa.europa.eu/system/files/reports/market_report_issue_6_v2.pdf GSA Market Report]</ref> To promote the development of EGNOS/EDAS based LBS applications, the EC funded R&D projects to provide toolkits for manufacturers.

In urban areas where acquiring satellite signals may be difficult and often provokes a loss of accuracy and performance degradation, EGNOS corrections could still be applied through the EDAS. Some of the R&D projects developed in this frames are listed bellow and a the complete list of ongoing projects is described in detail in the EC GNSS Applications site.
*''PERNASVIP'': to develop a GNSS-based mobility service dedicated to visually disabled pedestrians in urban environment.<ref name=" PERNASVIP Web">[http://pernasvip.di.uoa.gr/index.php PERNASVIP Web]</ref>
*''ATLAS'': concerns the development of an assurance and authentication service for GNSS-derived time and position information for use in liability-critical LBS applications across a wide variety of market sectors.<ref name=" ATLAS Project">[http://www.gsa.europa.eu/autenticated-time-and-location-location-based-application-and-services ATLAS Project]</ref>

===Road Applications===
Intelligent transport systems for road transport represent an important segment of the GNSS market. The wide range of applications do not only cover in-car navigation, but also user charging for an efficient use of the road infrastructure, fleet management and logistics.
Road User Charging (RUC) is becoming a strategy for authorities to manage increasingly congested road networks throughout Europe. This approach implies recording journey information by using a GNSS receiver embedded in an OBU and such solutions aided by EGNOS through EDAS have been widely analyzed.<ref name=" SIGNATURE">[http://www.nsl.eu.com/SIGNATURE/Space_Applications_Paper_010_Sheridan.pdf SignatureI]</ref>

The EC contributes to the development of EGNOS based technologies for road applications by promoting contracts in this framework. Some of these projects are briefly presented hereafter:
*''GINA'': aims at investigating the factors which could enable the application of GNSS-based road pricing followed by a nationwide demonstration in the Netherlands.<ref name=" GINA Project">[https://www.gsa.europa.eu/gnss-innovative-road-applications-0 GINA Project]</ref>
*''SIGNATURE'': develops new features improving road user charging in terms of charging accuracy (correct cost per trip),charging integrity (probability and amount of overcharging) and charging availability (amount of charged usage).<ref name=" SIGNATURE Project">[http://www.gsa.europa.eu/simple-gnss-assisted-and-trusted-receiver-0 SIGNATURE Project]</ref>
*''GALAPAGOS'': develops a positioning system for logistic applications with a special focus on container tracking.<ref name=" GALAPAGOS Project">[https://www.gsa.europa.eu/galileo-based-seamless-and-robust-positioning-applications-logistics-optimation-processes-0 GALAPAGOS Project]</ref>

===Rail and Maritime Applications===

[[File:container_ship.jpg| EGNOS EDAS – Maritime application |250px|thumb|right]]

The Mediterranean Introduction of GNSS Services (METIS)<ref name=" EGNOS demonstrations in the Mediterranean Area">[http://galileo.cs.telespazio.it/metis/public/METIS%20Leaflets/METIS-leaflet-CS.pdf EGNOS demonstrations in the Mediterranean Area]</ref> is an EGNOS demonstration that implements EGNOS use in transport domains over the Euro-Mediterranean area, to prepare market for Galileo.

This project relied not only on the EGNOS Signal In Space (SIS) but also on the distribution of EGNOS products via EDAS. Moreover it identified opportunities for EDAS in the Mediterranean area for the next decade by proving technical feasibility and quantified benefits.

SAFEPORT<ref name=" SAFEPORT Project">[http://www.gsa.europa.eu/safe-port-operations-using-egnos-sol-services SAFEPORT Project]</ref> is another project developed in the frame of Active Vessel Traffic Management that exploits the EGNOS accuracy, reliability and safety of life aspects by means of the EGNOS [[ EGNOS Safety of Life Service| Safety of Life]] and EDAS services.

===Civil protection and Goods Transportation===
In disaster situations, transport and communications infrastructures may become unavailable. However, relief operations need to rely on precise information as regards the location of rescue teams, topography or hazard maps.

Besides, Oil&Gas Companies and Special Transportation companies, with a key role played by National Authorities who have the need to monitor the status of the traffic of dangerous goods in national territories represent an important user segment for the application of the EDAS in safe transportation.<ref name=" EDAS Beta test findings">The EGNOS Service to Provide Ground Based Access to EGNOS – EDAS Beta test findings; Reinhard Blasi, GSA; Rafael Cardoso-Herce, Didier De Greef, ESSP; José Ramón López-Pérez, Francisco J. Jiménez-Roncero, AENA; Ángel Gavín-Alarcón, GMV; Monica Pesce, VVA</ref>

EDAS based tracking for the tracking & tracing services for the regulated control of dangerous material transport are presently demonstrated and proven in real-life cases involving Italian industry and authorities<ref name=" Transport of Dangerous material"> EGNOS in support of safe transport of Dangerous material: the joint experience of MENTORE and ENI; A. Di Fazio, Telespazio S.p.A; D. Pizzorni, Eni - Refining & Marketing, Logistica Secondari; M. Zazza, Ministero dei Trasporti Direzione Generale dei Sistemi Informatici e Statistici</ref> and it has been shown that commercial transport operators and users can benefit from effective shipment, whereas Law enforcement agencies take advantages from guaranteed information related to position, travelling times and route.

===Agriculture===
The costs associated with agriculture are on the rise and environmental demands are gaining ground by the day, meaning efficient and sustainable farming solutions are needed more than ever. EGNOS offers an affordable solution to move towards precision agriculture. In doing so, it enhances precision, eliminates waste, saves time, reduces fatigue, optimizes the use of equipment (thus extending its lifetime) and increases crop yields.
In order to demonstrate the impact of using EGNOS in the European agriculture, a few indicative data are given:
*A 30% is the reduction in the amount of labour needed for organic farming when using E-GNSS.
*A 82% is the percentage of European farmers relying on EGNOS to enhance precision agriculture
*A 21% is the yearly growth rate of revenues of Asset management in the period 2013-2025

===Aviation===
Aviation is the key market segment for European GNSS. In fact, EGNOS was designed for aviation. In brief, GNSS programmes like EGNOS have revolutionized the way we fly. It has created more access to small airports, increased safety and facilitated business across Europe. Across the commercial, regional, general and business aviation sectors and from airports to OEMs and the end user - everyone is benefitting from EGNOS.

===Timing and synchronization===
Computer and telecommunication networks around the world need extremely accurate clock references. EGNOS broadcasts the reliable time standard with the unprecedented accuracy that these networks demand.

===Mapping and surveying===
By providing sub-meter-level accuracy with minimal investment, EGNOS is a cost-effective, entry-level solution for the mapping and surveying sector. It satisfies the needs of mapping applications requiring enhanced GNSS positioning by providing added value – free of charge. As a result, municipalities, forestry authorities, utilities and other users are benefiting from EGNOS performance in mapping.

===Research and Development===
EDAS can facilitate EGNOS Evolution activities and a significant number of R&D activities. One such initiative is the magicSBAS product.
magicSBAS is an Augmentation System that collects GNSS data (measurements and ephemeris) from a regional network of reference stations, computes satellite orbits and clocks, ionospheric and integrity information, and broadcasts messages to the final user via Internet.<ref name=" GMV´s magicSBAS Web Site">[https://www.gmv.com/en/Products/magicSBAS/ GMV´s magicSBAS Web Site]</ref>

==Notes==
<references group="footnotes"/>
==References==
<references/>

[[Category:EGNOS|Commercial]]
[[Category:EGNOS Services|Commercial]]

EGNOS User Segment

2026-04-19T21:02:47Z

Gema.Cueto: Updated reference ICD/SDD links

{{Article Infobox2
|Category=EGNOS
|Editors=GMV
|Level=Basic
|YearOfPublication=2011
|Logo=GMV
|Title={{PAGENAME}}
}}
The EGNOS User segment is made of EGNOS receivers that enable their users to [[Accuracy|accurately]] compute their positions with [[Integrity|integrity]].

To receive EGNOS signals, an EGNOS compatible receiver is required; they are already available on the market from a variety of manufacturers. An EGNOS receiver is like a GPS receiver but with special software inside that allows the receiver to lock onto the code used by the EGNOS satellites and compute the EGNOS corrections to the GPS signals. An EGNOS receiver is the same size as a GPS receiver and uses the same type of antenna.<ref name=" ESA Navigation Portal">[https://egnos-user-support.essp-sas.eu/new_egnos_ops/ ESA Navigation Portal on EGNOS User Segment ]</ref>

==EGNOS Receivers and User Applications==

The European GNSS Agency (GSA)<ref name=" European GNSS Agency (GSA)">[http://www.gsa.europa.eu/ European GNSS Agency (GSA) ]</ref> and other institutions involved in the GNSS Industry have extensively worked on the definition of communication protocols, specification and user performances for EGNOS compatible [[EGNOS Receivers | receivers]].

Among the endless applications within the EGNOS user segment, [[ SISNET | SISNeT]] is a remarkable technology that combines the powerful capabilities of satellite navigation and the Internet. The highly accurate navigation information that comes from the EGNOS (European Geostationary Navigation Overlay Service) Signal-In-Space (SIS) is now available over the Internet and in real time via SISNeT.<ref name=" ESA Portal on SISNeT Project">[http://www.egnos-pro.esa.int/sisnet/index.html ESA Portal on SISNeT Project ]</ref>

==Errors Affecting User Positioning==
A GNSS receiver processes the individual satellite range measurements and combines them to compute an estimate of the user position (latitude, longitude, altitude, and user
clock bias) in a given geographical coordinate reference frame.<ref name=" EGNOS SoL SDD"/>

The estimation of the satellite-to-user range is based on the measurement of the propagation time of the signal and a number of error sources affect the accuracy of these measurements:<ref name=" EGNOS SoL SDD">[https://egnos.gsc-europa.eu/sites/default/files/documents/egnos_sol_sdd_in_force.pdf?v=1726657048 EGNOS Safety of Life (SoL) Service Definition Document (SDD) ]</ref>
* Satellite clocks: any error in the synchronisation of the different satellite clocks will have a direct effect on the range measurement accuracy. These errors are similar for all users able to view a given satellite.
* Signal distortions: any failure affecting the shape of the broadcast signal may have an impact on the propagation time determination in the user receiver.
* Satellite position errors: if the spacecraft orbits are not properly determined by the system’s ground segment, the user will not be able to precisely establish the spacecraft location at any given point in time. This will introduce an error when computing the user position. The size of the error affecting the range measurements depends on the user’s location.
* Ionospheric effects: The ionosphere is the ionised layer of the Earth atmosphere located from around 60 kilometres to several thousand kilometres. When propagation through the ionosphere, navigation signals are disturbed, resulting in range measurement errors or reduced availability. Please refer to the article ''[[Ionospheric Delay]]'' for further information.
* Tropospheric effects: The troposphere is the lower part of the atmosphere where most weather phenomena take place. The signal propagation in this region will be affected by specific atmospheric conditions (e.g. temperature, humidity…) and will result in range measurement errors. Tropospheric effects are further described in the article ''[[Tropospheric Delay]]''.
* Local effects: When propagating in the local environment of a user receiver, navigation signals are prone to reflections or obstructions from the ground or nearby objects (buildings, vehicles...).
* Thermal noise, interference and user receiver design: the navigation signals have an extremely low power level when they reach the user receiver.

When computing its position the user receiver combines the range measurements from the different satellites in view. Through this process, the individual errors affecting each range measurement are combined which results in an aggregate error in the position domain. The statistical relationship between the average range domain error and the position error is given by a factor that depends on the satellite geometry; this factor is named DOP ([[Positioning Error|Dilution Of Precision]]).

==Credits==
This article contains some verbatim extracts taken from ESA navigation web pages<ref name=" ESA Navigation Portal"/> and EGNOS SoL Service Definition Document<ref name=" EGNOS SoL SDD"/> according to the references cited.

==Notes==
<references group="footnotes"/>
==References==
<references/>

[[Category:EGNOS|User]]
[[Category:EGNOS Architecture|User]]

SISNET

2026-04-19T20:58:38Z

Gema.Cueto: Updated reference ICD/SDD links

{{Article Infobox2
|Category=EGNOS
|Editors=GMV
|Level=Basic
|YearOfPublication=2011
|Logo=GMV
|Title={{PAGENAME}}
}}
SISNeT is a technology that combines the powerful capabilities of satellite navigation and the Internet. The accurate navigation and integrity information that comes from the EGNOS (European Geostationary Navigation Overlay Service) Signal-In-Space (SIS) is available over the Internet and in real time via SISNeT.<ref name=" ESA SISNeT Portal">[http://www.egnos-pro.esa.int/sisnet/index.html ESA SISNeT Portal ]</ref> Today, SISNeT is included in [[EGNOS Data Access Service (EDAS)|EDAS service]].

EGNOS broadcasts augmentation signals for GNSS through Geostationary Earth Orbit (GEO) satellites. GEO broadcasting is proved to be an efficient strategy for avionic applications and other modes of transport. For some applications, though, it may be of interest to complement GEO broadcasting through other transmission means. For instance, building obstacles in cities or rural canyons may difficult the GEO reception. In those situations, complementary real-time Internet-based broadcasting of the EGNOS signal is of major interest as a way to continue taking the most of the EGNOS potential, irrespectively of the user environment.<ref name=" The ESA SISNeT Project: Current Status and Future Plans">The ESA SISNeT Project: Current Status and Future Plans; Félix Torán-Martí and Javier Ventura-Traveset ESA GNSS-1 Project Office. European Space Agency (ESA). Toulouse (France). </ref>

Responding to that need, ESA developed and launched the SISNeT service in 2002. SISNeT allows retrieving the EGNOS messages across the Internet in real-time, usually through wireless networks, like GSM or GPRS. Thanks to SISNeT, any user with access to the Internet (e.g. through wireless GSM or GPRS networks) may access the EGNOS product, irrespectively of the GEO visibility conditions.

==SISNeT Advantages==

In the early days of SISNeT, advanced simulation activities revealed that the combination of EGNOS and the almost unlimited capabilities of the Internet could open the door to a lot of innovative applications for Satellite Navigation. The evolution of SISNeT to the date has demonstrated and justified what simulations were anticipating, mainly thanks to:

* The launch of a number of ESA contracts with European industry, on SISNeT developments.
* The interest of worldwide companies, organisations and universities on applying SISNeT to a large variety of applications, research and development projects.
* The ESA internal work on SISNeT.

In fact, new application fields based on SISNeT were identified, like educational applications, help to impaired people, quick initialisation of SBAS receivers, etc. The possibilities of SISNeT revealed to be beyond ESA initial expectations.

On the other hand, the Scientific and Engineering community may find major advantages in using SISNeT: the EGNOS signal can be received and processed without having to invest in an EGNOS receiver. Just a connection to the Internet is necessary. These benefits are also applicable to Educational environments (e.g. laboratory exercises based on the EGNOS signal do not imply acquiring receivers, only requiring computers connected to the Internet).

Another advantage is centred in the low bandwidth requirements of SISNeT: the transfer rate ranges from 300 bps to 700 bps, being 470 bps the average value. These characteristics make SISNeT very adequate to be used with GSM / GPRS wireless networks.

==Current SISNeT Status==

For a wide range of EGNOS applications it may be of interest to complement GEO broadcasting through other transmission means. For instance, building obstacles in cities or rural canyons may difficult the GEO reception. In those situations, complementary means of broadcasting (e.g. FM, Digital Audio Broadcasting – DAB – and the Internet) have a remarkable interest. In this context, the European Space Agency (ESA)<ref name=" ESA Web Site">[http://www.esa.int/esaCP/index.html ESA Web Site ]</ref> launched an internal project to provide access to the EGNOS messages in real time through the Internet. The product of this project was a new technology, called SISNeT (Signal in Space through the Internet), whose interest has greatly grown since the initial SISNet service was put in place by ESA in 2001.

A first prototype of the SISNeT concept was set-up by the ESA GNSS-1 Project Office, in 2001. Since February 2002, the SISNeT service is accessible through the open Internet, via an authentication procedure.
Currently, SISNet is nowadays integrated in EDAS service. Please refer to EDAS Service Definition document<ref name=" EDAS SDD">[https://egnos.gsc-europa.eu/sites/default/files/documents/egnos_edas_sdd_in_force.pdf?v=1734519406 EDAS SDD ]</ref> for guidelines for the access and usage of the EDAS SISNet service.

The SISNet status can be consulted through EDAS in EGNOS monitoring website from ESSP.<ref name=" EDAS Status">[https://egnos-user-support.essp-sas.eu/new_egnos_ops/services/edas-service/realtime EDAS Status ]</ref>

==Deployed SISNeT Applications==

The SISNeT project can grant important advantages to the GPS land-user community as a user equipped with a GPS receiver and a GSM (or GPRS) modem can access the SISNeT services, thus being able to benefit from the EGNOS augmentation signals, even under situations of GEO blocking. A series of SISNeT based projects were successfully completed, some of which are briefly described hereafter:<ref name=" The ESA SISNeT Project: Current Status and Future Plans"></ref>

[[File: ShPIDER_receiver.JPG| SISNeT-based ShPIDER receiver |250px|thumb|right]]

* '''Handheld SISNeT receiver'''.<ref name=" Handheld Internet-Based EGNOS Receiver">Handheld Internet-Based EGNOS Receiver: The First Product of the ESA SISNET Technology; F. Toran, J. Ventura-Traveset and R. Chen; GNSS 2003, Graz (Austria), 22 – 25 April 2003. </ref> <ref name=" Navigate via the Web with the SISNeT receiver">[http://www.esa.int/Our_Activities/Navigation/Navigate_via_the_web_with_the_SISNeT_receiver Navigate via the Web with the SISNeT receiver: ESA Press Release, 6 September 2002, European Space Agency.]</ref> <ref name=" Access to the EGNOS Signal In Space Over Mobile-IP">Access to the EGNOS Signal In Space Over Mobile-IP; R. Chen, F. Toran-Marti and J. Ventura-Traveset. GPS Solutions (2003). </ref> This device is based on a Pocket PC Personal Digital Assistant (PDA) device. It includes a GPS card, and the Internet is reached through a GSM / GPRS wireless modem. Specific software is embedded, combining GPS measurements with the EGNOS corrections got via SISNeT. As a result, position accuracy is considerably improved.

* '''SISNeT technology applied to fleet management'''.<ref name=" Toulouse bus test-drives European satellite navigation">[http://www.esa.int/Our_Activities/Navigation/Toulouse_bus_test-drives_European_satellite_navigation Toulouse bus test-drives European satellite navigation; ESA Press Release, 14 February 2003.]</ref> A one-box handheld SISNeT receiver was developed, based on a Psion NetPad device, equipped with the Windows CE .net operating system. A mechanical adaptation was made to integrate a GPS receiver chipset. The link to the Internet is achieved through an integrated GSM / GPRS modem. Almost any commercial GIS software can be used with SISNeT positioning, thanks to a specific driver.

* '''Application of the SISNeT technology to help blind pedestrians'''. This activity consisted on assessing the feasibility of applying the SISNeT concept to improve the performance of a navigation device for the blind. The selected device, called TORMES, was developed by the Spanish company GMV and ONCE (the Spanish organisation for the blind) before the start of the activity.<ref name=" Space technology to help the blind">[http://www.esa.int/esaNA/ESAKN58708D_egnos_0.html Space technology to help the blind; ESA Press Release, 30 December 2003.]</ref> <ref name=" Blind Pedestrian Navigator: Operating Features, Performances and EGNOS / SISNET Benefits">Blind Pedestrian Navigator: Operating Features, Performances and EGNOS / SISNET Benefits; Catalina A., March J., Davila R., Paniagua J., Busnadiego C., Ventura-Traveset J., Toran-Marti F., Fernandez-Coya J.L., Lorente J.L.; Proceedings of GNSS 2003, Graz (Austria), 22 – 25 April 2003.</ref>

* '''EDAS SISNeT Service''': The EDAS SISNeT service provides access to messages from EGNOS GEO satellites transmitted through the Internet using the SISNeT protocol, a full description of which is available in the SISNeT User Interface Document. Specific guidelines on how to access and use the EDAS SISNeT service are available in the EDAS SISNeT User Information Package. <ref>https://egnos-user-support.essp-sas.eu/new_egnos_ops/services/about-edas</ref>

==Potential SISNeT Applications==

ESA also identified additional benefits that could be obtained from SISNeT, remarking the following:

* The indoor penetration of wireless networks as GSM or GPRS offers a lot of benefits for SBAS receiver initialisation. For vehicles, the SBAS receiver can be initialised in the garage, being ready to use (with EGNOS corrections) once reaching the street.
* In addition, when crossing long tunnels (or other segments with no GPS / GEO satellite visibility) SBAS/SISNeT receiver can start getting the necessary information before leaving the tunnel, since GSM /GPRS signals are normally accessible before reaching the exit. Considering the capability to retrieve previously broadcast messages via SISNeT, the SBAS system can be immediately used after leaving the tunnel in most of the cases, and the benefits of GEO ranging available without delay, just immediately after the EGNOS GEO(s) are again in visibility.
* Prior to reaching the urban environment (e.g. while a vehicle is in the garage or a person is inside a building), the GPS ephemeris information can be initialised from SISNeT, instead of waiting for the GPS message to be received (once on the urban scenario), reducing very much then the time to first fix.

SISNeT started as a prototype system, although currently it is an operational one.

==Credits==
This article has been mainly based on information published by ESA, according to the references cited.

==Notes==
<references group="footnotes"/>
==References==
<references/>

[[Category:EGNOS]]
[[Category:EGNOS Architecture]]
[[Category:EGNOS User Segment]]

EGNOS Architecture

2026-04-19T20:54:27Z

Gema.Cueto: Undo revision 16738 by Gema.Cueto (talk)

{{Article Infobox2
|Category=EGNOS
|Editors=GMV
|Level=Basic
|YearOfPublication=2011
|Logo=GMV
|Title={{PAGENAME}}
}}
The goal of [[EGNOS General Introduction|EGNOS]] (European Geostationary Navigation Overlay Service) is to augment GNSS in order to improve the navigation performances in terms of accuracy and integrity (with the required levels of availability and continuity of service) over the European Civil Aviation Conference (ECAC) Region and to be expandable over neighbouring regions. Current EGNOS only augments GPS satellites on L1 signal.

These augmentations are obtained by providing orbit and clock corrections for GNSS satellites and also correcting the ionospheric delays affecting the signal paths to the users. The complex message broadcast by EGNOS GEOs also include Integrity data which allow to bound the remaining errors with a high level of confidence.

The EGNOS architecture is very complex and highly redundant. It is currently composed by more than 40 elements deployed in more than 20 countries. EGNOS has been designed to meet the international SBAS standards and performs the following tasks:
* Collect GPS/GLONASS/GEO signals and data.
* Estimate the integrity data and WAD (Wide Area Differential) corrections for the service area.
* Transmit to the users, via the GEO satellites, a GPS-like signal, augmented with integrity and correction messages.
* Verify the correctness of these integrity and correction messages.

For the next generation of the EGNOS augmentation system (EGNOS V3), the GSA requested the complete overhaul of the EGNOS ground segment, which was becoming obsolete. This modernization programme will see the deployment of EGNOS V3 in ground stations at more than 50 sites in Europe, and surrounding countries.

The GSA also requested the development of new EGNOS capabilities to support the augmentation of a second GPS signal (L5) and of the Galileo signals E1-E5. Another requirement is that the system is made more robust, to deal with the growing number of users numbers and to reflect their increasing dependence on EGNOS and its ground applications - in some countries (e.g. France) instrument landing systems (ILS) are being decommissioned on several airports because the civil aviation authorities have decided instead to rely on EGNOS.

The current EGNOS augments the accuracy of GPS signals across Europe and informs users of their current reliability level within six seconds. EGNOS belongs to a family of systems called Satellite Based Augmentation Systems (SBAS).

EGNOS V3 is planned to provide the aviation community with advanced Safety of Life (SoL) services as well as new services to maritime and land users. EGNOS V3 will provide augmented operational SoL services over Europe that improve the accuracy and availability of user positioning services from existing Global Navigation Satellite Systems (Galileo and GPS) and provides crucial integrity messages to EGNOS users with alerts within a few seconds in case of system degradation, consolidating EGNOS’ position as one of the leading edge GNSS Systems in the future.

EGNOS V3 will thus offer improved SoL services performances (where people’s lives are potentially at stake) over Europe to Civil Aviation community and new applications for maritime or land users, and will improve robustness against increasing security risks, in particular cyber-security risks.

EGNOS V3 will ensure a full continuity of service for the next decade and will be within the first operational SBAS systems implementing the dual frequency and multi constellation world standard, with both GPS and Galileo, replacing EGNOS V2 which has been in operation since 2011.<ref name=" AIRBUS-EGNOS V3 RIMS+NLES Performance Enginee ">Analysis Of Safety Of Life Service Provision For The European GNSS Elements, EGPC-10-04-23-04, 16 April 2010, European GNSS Programmes Committee, European Commission </ref>

==Architecture Overview==

[[File:EGNOS_architecture.JPG| EGNOS functional architecture |300px|thumb|right]]
The EGNOS system is directly decomposed in its four segments, a Ground Segment, a Space Segment, a User Segment and a Support Segment:<ref name=" The EGNOS System Architecture explained">The EGNOS System Architecture explained; Didier Flament, Jean Poumailloux, Jean-Louis Damidaux, Stéphane Lannelongue Alcatel Alenia Space, France ; Javier Ventura-Traveset, P. Michel and C. Montefusco ; European Space Agency, EGNOS Project Office; </ref><ref name=" EGNOS SoL SDD">[http://www.essp-sas.eu/service_definition_documents EGNOS Service Definition Documents (SDD) ]</ref>

* The [[EGNOS Ground Segment |Ground Segment]] computes precise differential corrections and integrity bounds and makes all these information available to users through a broadcast by the Space Segment.
* The [[EGNOS Space Segment |Space segment]], using GEO satellites, provides redundant data transmission channel to broadcast toward EGNOS user messages containing differential corrections with the associated integrity information.
* The [[EGNOS User Segment |User Segment]] is made of EGNOS receivers which enable EGNOS users to accurately compute their position.
* The Support Segment contains off-line facilities supporting activities such as performance analysis, troubleshooting, maintenance and qualification.

==EGNOS Space Segment==

The [[EGNOS Space Segment | EGNOS Space Segment]] comprises 3 GEO satellites broadcasting corrections and integrity information for GPS satellites in the L1 frequency band (1575,42 MHz).
This configuration provides a high level of redundancy over the whole service area in case of a geostationary satellite link failure. The EGNOS operations are handled in such a way that, at any point in time, typically two of the three GEOs broadcast an operational signal, the others broadcasting test signal. Since it is only necessary to track a single GEO satellite link to benefit from the EGNOS SoL, this secures a switching capability in case of interruption and ensures a high level of continuity of service. The configuration of the GEOs in operation does not change frequently but possible updates are nevertheless reported to users by the EGNOS Service Provider.

It is intended that the EGNOS space segment will be replenished over time in order to maintain a similar level of redundancy. The exact orbital location of future satellites may
vary, though this will not impact the service offered to users. Similarly, different PRN code numbers may be assigned to future GEOs. However, all SBAS user receivers
are designed to automatically detect and use any code in a pre-allocated set reserved for SBAS. Such [[EGNOS_Future_and_Evolutions|evolutions]] will therefore be transparent for end users and will not
necessitate any human intervention or change of receiving equipment.

The GSA’s request for EGNOS V3 development is part of its overall EGNOS modernization program that also includes renewal of the space segment. As part of this program, the GSA contracted Eutelsat for the preparation and service provision phases of the EGNOS GEO-3 payload, to be hosted on the EUTELSAT 5.<ref name=" INSIDE-GNSS: EGNOS V3">[http://insidegnss.com/esa-airbus-sign-contract-for-egnos-v3-upgrades/ INSIDE-GNSS: EGNOS V3]</ref>

==EGNOS Ground Segment==
The [[EGNOS Ground Segment |EGNOS Ground Segment]] comprises a network of Ranging Integrity Monitoring Stations (RIMS), two Mission Control Centres (MCC), six Navigation Land Earth Stations (NLES), and the EGNOS Wide Area Network (EWAN) which provides the communication network for all the components of the Ground Segment. Two additional facilities are also deployed as part of the ground segment to support system operations and service provision, namely the Performance Assessment and Checkout Facility (PACF) and the Application Specific Qualification Facility (ASQF), which are operated by the EGNOS Service Provider.<ref name=" ESSP HomePage">[https://www.gsa.europa.eu/european-gnss/egnos/egnos-system EGNOS System in EGNOS Service Provider website ]</ref>

The EGNOS system is a widely distributed and redundant system. Data flows from one subsystem to another subsystem have different level of criticality.

[[File:EGNOS_data_Flow.JPG| EGNOS Data flow |350px|thumb|right]]

The main EGNOS functions are carried out by the Ground Segment through the following critical subsystems: the RIMS stations, the CPF units and the NLES stations. The Ground Segment is a periodic synchronous and pipelined system. The synchronization of subsystems located in widely separated geographic places is referred to
the GPS time by means of GPS receivers providing a 1 PPS (one Pulse Per Second) synchronization pulse to the associated subsystem.

Another feature of the EGNOS Ground Segment is that all Monitoring and Control (M&C) functions performed by humans (non-automatic functions) are centralized and implemented
in the CCF subsystems, which is outside of the critical data flow. Operators on duty in another CCF (hot backup) are ready to take over the system monitoring and control if the master CCF fails. Remaining two CCF (cold backup) can be reactivated if the master one fails.

In the EGNOS data flow representation, the real time critical data flow is indicated in red whereas the non-critical data flow is indicated in green.

The sub-systems involved in the processing of the critical data are responsible for the achievement of the main EGNOS system performance (accuracy, integrity, continuity, time to alarm, and service coverage) while the sub-systems involved in the management of non-critical data perform the Monitoring and Control (M&C) and archive functions.

The EGNOS Ground Segment includes the following support facilities (EGNOS Support Segment):
* PACF: Performance Assessment and Check-out Facility, provides support to EGNOS management in such area as performances analysis, troubleshooting, operational procedures as well as upgrade of specification and validation, and support to maintenance.
* ASQF: Application Specific Qualification Facility provides civil aviation and aeronautical certification authorities with the tools to qualify validate and certify the different EGNOS applications.

Due to the implementation of EGNOS V3, the RIMS and NLES performance engineering have to be updated in order to be responsible for:

*Monitoring the proper implementation of the RIMS and NLES specifications imposed by EGNOS V3 system.
*Characterizing the RIMS and NLES performances as achieved by the implemented RIMS and NLES (incl. characterization of RIMS and NLES environment) used as input for EGNOS V3 system performance analysis.
*Maintaining and updating RIMS and NLES specifications as needed to support EGNOS V3 system performance analysis (this includes survey of specifications provided as CFI by the customer (e.g. scintillation specifications, RIMS and NLES RFI environment specifications, User Rx standards (e.g. new L5 DFMC SBAS MOPS), survey of NLES specification provided by the Customer).

==EGNOS User Segment==
The [[EGNOS User Segment | EGNOS User Segment]] consists of the GNSS receivers that enable their users to accurately compute their positions using EGNOS corrections. It is important to bear in mind that a GNSS receiver only monitors signals sent by the satellites and does not establish any contact with them. Therefore, a GNSS receiver cannot be used by a third party to find out a user’s position without his knowledge.<ref name=" USER GUIDE FOR EGNOS APPLICATION DEVELOPERS">[http://www.cnes-csg.fr/automne_modules_files/standard/public/p7853_cb8d73df13dfd104092d3f8c5cc2062bguide_egnos_2011_GB_112_P.pdf USER GUIDE FOR EGNOS APPLICATION DEVELOPERS ]</ref>

To receive EGNOS signals an EGNOS compatible receiver is required. There are many receivers available on the market from a variety of manufacturers.
An EGNOS receiver is like a GNSS receiver but with special software inside that allows the receiver to lock onto the code used by the EGNOS satellites and compute the EGNOS corrections to the GNSS signals. Apart from this, an EGNOS receiver is just like a GNSS receiver. This means that it can pick up GPS signals as well. An EGNOS receiver is the same size as a GPS receiver and uses the same type of antenna.<ref name=" ESA Navigation Site on EGNOS User Segment">[http://www.esa.int/esaNA/ESAQZ20VMOC_index_0.html ESA Navigation Site on EGNOS User Segment ]</ref>

To test the EGNOS receiver, special prototypes have been developed with extensive capabilities to log and analyze data.

EGNOS V3 will provide enhanced performances and robustness in the whole GEO broadcast area for those users equipped with standard space based augmentation system (SBAS) receivers capable of both Galileo and GPS. Moreover the baseline V3 system architecture will be modular and upgradeable in time in order to progressively accommodate and support a very wide span of brand new GNSS services for various user communities.<ref name=" DLR-Institute of Communications and Navigation">[https://www.dlr.de/kn/en/desktopdefault.aspx/tabid-4309/3222_read-32227/ DLR-Institute of Communications and Navigation]</ref>

==Notes==
<references group="footnotes"/>
==References==
<references/>

[[Category:EGNOS]]
[[Category:EGNOS Architecture]]

EGNOS Architecture

2026-04-19T20:49:52Z

Gema.Cueto: Updated reference ICD/SDD links

{{Article Infobox2
|Category=EGNOS
|Editors=GMV
|Level=Basic
|YearOfPublication=2011
|Logo=GMV
|Title={{PAGENAME}}
}}
The goal of [[EGNOS General Introduction|EGNOS]] (European Geostationary Navigation Overlay Service) is to augment GNSS in order to improve the navigation performances in terms of accuracy and integrity (with the required levels of availability and continuity of service) over the European Civil Aviation Conference (ECAC) Region and to be expandable over neighbouring regions. Current EGNOS only augments GPS satellites on L1 signal.

These augmentations are obtained by providing orbit and clock corrections for GNSS satellites and also correcting the ionospheric delays affecting the signal paths to the users. The complex message broadcast by EGNOS GEOs also include Integrity data which allow to bound the remaining errors with a high level of confidence.

The EGNOS architecture is very complex and highly redundant. It is currently composed by more than 40 elements deployed in more than 20 countries. EGNOS has been designed to meet the international SBAS standards and performs the following tasks:
* Collect GPS/GLONASS/GEO signals and data.
* Estimate the integrity data and WAD (Wide Area Differential) corrections for the service area.
* Transmit to the users, via the GEO satellites, a GPS-like signal, augmented with integrity and correction messages.
* Verify the correctness of these integrity and correction messages.

For the next generation of the EGNOS augmentation system (EGNOS V3), the GSA requested the complete overhaul of the EGNOS ground segment, which was becoming obsolete. This modernization programme will see the deployment of EGNOS V3 in ground stations at more than 50 sites in Europe, and surrounding countries.

The GSA also requested the development of new EGNOS capabilities to support the augmentation of a second GPS signal (L5) and of the Galileo signals E1-E5. Another requirement is that the system is made more robust, to deal with the growing number of users numbers and to reflect their increasing dependence on EGNOS and its ground applications - in some countries (e.g. France) instrument landing systems (ILS) are being decommissioned on several airports because the civil aviation authorities have decided instead to rely on EGNOS.

The current EGNOS augments the accuracy of GPS signals across Europe and informs users of their current reliability level within six seconds. EGNOS belongs to a family of systems called Satellite Based Augmentation Systems (SBAS).

EGNOS V3 is planned to provide the aviation community with advanced Safety of Life (SoL) services as well as new services to maritime and land users. EGNOS V3 will provide augmented operational SoL services over Europe that improve the accuracy and availability of user positioning services from existing Global Navigation Satellite Systems (Galileo and GPS) and provides crucial integrity messages to EGNOS users with alerts within a few seconds in case of system degradation, consolidating EGNOS’ position as one of the leading edge GNSS Systems in the future.

EGNOS V3 will thus offer improved SoL services performances (where people’s lives are potentially at stake) over Europe to Civil Aviation community and new applications for maritime or land users, and will improve robustness against increasing security risks, in particular cyber-security risks.

EGNOS V3 will ensure a full continuity of service for the next decade and will be within the first operational SBAS systems implementing the dual frequency and multi constellation world standard, with both GPS and Galileo, replacing EGNOS V2 which has been in operation since 2011.<ref name=" AIRBUS-EGNOS V3 RIMS+NLES Performance Enginee ">Analysis Of Safety Of Life Service Provision For The European GNSS Elements, EGPC-10-04-23-04, 16 April 2010, European GNSS Programmes Committee, European Commission </ref>

==Architecture Overview==

[[File:EGNOS_architecture.JPG| EGNOS functional architecture |300px|thumb|right]]
The EGNOS system is directly decomposed in its four segments, a Ground Segment, a Space Segment, a User Segment and a Support Segment:<ref name=" The EGNOS System Architecture explained">The EGNOS System Architecture explained; Didier Flament, Jean Poumailloux, Jean-Louis Damidaux, Stéphane Lannelongue Alcatel Alenia Space, France ; Javier Ventura-Traveset, P. Michel and C. Montefusco ; European Space Agency, EGNOS Project Office; </ref><ref name=" EGNOS SoL SDD">[https://www.gsc-europa.eu/electronic-library/programme-reference-documents/egnos-in-force EGNOS Service Definition Documents (SDD) ]</ref>

* The [[EGNOS Ground Segment |Ground Segment]] computes precise differential corrections and integrity bounds and makes all these information available to users through a broadcast by the Space Segment.
* The [[EGNOS Space Segment |Space segment]], using GEO satellites, provides redundant data transmission channel to broadcast toward EGNOS user messages containing differential corrections with the associated integrity information.
* The [[EGNOS User Segment |User Segment]] is made of EGNOS receivers which enable EGNOS users to accurately compute their position.
* The Support Segment contains off-line facilities supporting activities such as performance analysis, troubleshooting, maintenance and qualification.

==EGNOS Space Segment==

The [[EGNOS Space Segment | EGNOS Space Segment]] comprises 3 GEO satellites broadcasting corrections and integrity information for GPS satellites in the L1 frequency band (1575,42 MHz).
This configuration provides a high level of redundancy over the whole service area in case of a geostationary satellite link failure. The EGNOS operations are handled in such a way that, at any point in time, typically two of the three GEOs broadcast an operational signal, the others broadcasting test signal. Since it is only necessary to track a single GEO satellite link to benefit from the EGNOS SoL, this secures a switching capability in case of interruption and ensures a high level of continuity of service. The configuration of the GEOs in operation does not change frequently but possible updates are nevertheless reported to users by the EGNOS Service Provider.

It is intended that the EGNOS space segment will be replenished over time in order to maintain a similar level of redundancy. The exact orbital location of future satellites may
vary, though this will not impact the service offered to users. Similarly, different PRN code numbers may be assigned to future GEOs. However, all SBAS user receivers
are designed to automatically detect and use any code in a pre-allocated set reserved for SBAS. Such [[EGNOS_Future_and_Evolutions|evolutions]] will therefore be transparent for end users and will not
necessitate any human intervention or change of receiving equipment.

The GSA’s request for EGNOS V3 development is part of its overall EGNOS modernization program that also includes renewal of the space segment. As part of this program, the GSA contracted Eutelsat for the preparation and service provision phases of the EGNOS GEO-3 payload, to be hosted on the EUTELSAT 5.<ref name=" INSIDE-GNSS: EGNOS V3">[http://insidegnss.com/esa-airbus-sign-contract-for-egnos-v3-upgrades/ INSIDE-GNSS: EGNOS V3]</ref>

==EGNOS Ground Segment==
The [[EGNOS Ground Segment |EGNOS Ground Segment]] comprises a network of Ranging Integrity Monitoring Stations (RIMS), two Mission Control Centres (MCC), six Navigation Land Earth Stations (NLES), and the EGNOS Wide Area Network (EWAN) which provides the communication network for all the components of the Ground Segment. Two additional facilities are also deployed as part of the ground segment to support system operations and service provision, namely the Performance Assessment and Checkout Facility (PACF) and the Application Specific Qualification Facility (ASQF), which are operated by the EGNOS Service Provider.<ref name=" ESSP HomePage">[https://www.gsa.europa.eu/european-gnss/egnos/egnos-system EGNOS System in EGNOS Service Provider website ]</ref>

The EGNOS system is a widely distributed and redundant system. Data flows from one subsystem to another subsystem have different level of criticality.

[[File:EGNOS_data_Flow.JPG| EGNOS Data flow |350px|thumb|right]]

The main EGNOS functions are carried out by the Ground Segment through the following critical subsystems: the RIMS stations, the CPF units and the NLES stations. The Ground Segment is a periodic synchronous and pipelined system. The synchronization of subsystems located in widely separated geographic places is referred to
the GPS time by means of GPS receivers providing a 1 PPS (one Pulse Per Second) synchronization pulse to the associated subsystem.

Another feature of the EGNOS Ground Segment is that all Monitoring and Control (M&C) functions performed by humans (non-automatic functions) are centralized and implemented
in the CCF subsystems, which is outside of the critical data flow. Operators on duty in another CCF (hot backup) are ready to take over the system monitoring and control if the master CCF fails. Remaining two CCF (cold backup) can be reactivated if the master one fails.

In the EGNOS data flow representation, the real time critical data flow is indicated in red whereas the non-critical data flow is indicated in green.

The sub-systems involved in the processing of the critical data are responsible for the achievement of the main EGNOS system performance (accuracy, integrity, continuity, time to alarm, and service coverage) while the sub-systems involved in the management of non-critical data perform the Monitoring and Control (M&C) and archive functions.

The EGNOS Ground Segment includes the following support facilities (EGNOS Support Segment):
* PACF: Performance Assessment and Check-out Facility, provides support to EGNOS management in such area as performances analysis, troubleshooting, operational procedures as well as upgrade of specification and validation, and support to maintenance.
* ASQF: Application Specific Qualification Facility provides civil aviation and aeronautical certification authorities with the tools to qualify validate and certify the different EGNOS applications.

Due to the implementation of EGNOS V3, the RIMS and NLES performance engineering have to be updated in order to be responsible for:

*Monitoring the proper implementation of the RIMS and NLES specifications imposed by EGNOS V3 system.
*Characterizing the RIMS and NLES performances as achieved by the implemented RIMS and NLES (incl. characterization of RIMS and NLES environment) used as input for EGNOS V3 system performance analysis.
*Maintaining and updating RIMS and NLES specifications as needed to support EGNOS V3 system performance analysis (this includes survey of specifications provided as CFI by the customer (e.g. scintillation specifications, RIMS and NLES RFI environment specifications, User Rx standards (e.g. new L5 DFMC SBAS MOPS), survey of NLES specification provided by the Customer).

==EGNOS User Segment==
The [[EGNOS User Segment | EGNOS User Segment]] consists of the GNSS receivers that enable their users to accurately compute their positions using EGNOS corrections. It is important to bear in mind that a GNSS receiver only monitors signals sent by the satellites and does not establish any contact with them. Therefore, a GNSS receiver cannot be used by a third party to find out a user’s position without his knowledge.<ref name=" USER GUIDE FOR EGNOS APPLICATION DEVELOPERS">[http://www.cnes-csg.fr/automne_modules_files/standard/public/p7853_cb8d73df13dfd104092d3f8c5cc2062bguide_egnos_2011_GB_112_P.pdf USER GUIDE FOR EGNOS APPLICATION DEVELOPERS ]</ref>

To receive EGNOS signals an EGNOS compatible receiver is required. There are many receivers available on the market from a variety of manufacturers.
An EGNOS receiver is like a GNSS receiver but with special software inside that allows the receiver to lock onto the code used by the EGNOS satellites and compute the EGNOS corrections to the GNSS signals. Apart from this, an EGNOS receiver is just like a GNSS receiver. This means that it can pick up GPS signals as well. An EGNOS receiver is the same size as a GPS receiver and uses the same type of antenna.<ref name=" ESA Navigation Site on EGNOS User Segment">[http://www.esa.int/esaNA/ESAQZ20VMOC_index_0.html ESA Navigation Site on EGNOS User Segment ]</ref>

To test the EGNOS receiver, special prototypes have been developed with extensive capabilities to log and analyze data.

EGNOS V3 will provide enhanced performances and robustness in the whole GEO broadcast area for those users equipped with standard space based augmentation system (SBAS) receivers capable of both Galileo and GPS. Moreover the baseline V3 system architecture will be modular and upgradeable in time in order to progressively accommodate and support a very wide span of brand new GNSS services for various user communities.<ref name=" DLR-Institute of Communications and Navigation">[https://www.dlr.de/kn/en/desktopdefault.aspx/tabid-4309/3222_read-32227/ DLR-Institute of Communications and Navigation]</ref>

==Notes==
<references group="footnotes"/>
==References==
<references/>

[[Category:EGNOS]]
[[Category:EGNOS Architecture]]

BeiDou Signal Plan

2026-04-17T14:27:46Z

Gema.Cueto: Updated reference ICD/SDD links

{{Article Infobox2
|Category=Fundamentals
|Authors=J.A Ávila Rodríguez, University FAF Munich, Germany.
|Level=Advanced
|YearOfPublication=2011
|Title={{PAGENAME}}
}}
Presently, the in-orbit operational BDS satellites providing open services include 5 GEO satellites, 7 IGSO satellites and 21 MEO satellites, which can be further divided as 15 BDS-2 satellites ( 5 BDS-2G, 7 BDS-2I, 3 BDS-2M) and 18 BDS-3 satellites (BDS-3M). In addition to B1I and B2I signals, the B1C and B2a ones have started broadcasting by the BDS-3M satellites<ref name="BeiDou Navigation Satellite System Open Service Performance Standard ">[http://en.beidou.gov.cn/SYSTEMS/Officialdocument/202110/P020211014595952404052.pdf] BeiDou Navigation Satellite System Open Service Performance Standard</ref>.

== BeiDou B1I Band ==
The B1I signal is composed of the carrier frequency, ranging code and navigation message. The ranging code and navigation message are modulated on carrier. The B1I signal is expressed as follows<ref name="B1I">[http://en.beidou.gov.cn/SYSTEMS/Officialdocument/201902/P020190227601370045731.pdf]BeiDou Navigation Satellite System Signal In Space Interface Control Document Open Service Signal B1I (Version 3.0) </ref>:

SjB1I (t) = AB1ICjB1I(t)DjB1I(t)cos(2πf1t + ѰjB1I)

Where: 
• Superscript j: satellite number. 
• AB1I : amplitude of B1I. 
• CB1I : ranging code of B1I. 
• DB1I : data modulated on ranging code of B1I. 
• f1 : carrier initial phase of B1I. 
• ѰB1I : carrier initial phase of B1I. 

To conclude some technical characteristics of the BeiDou B1 signals are given next:

{| class="wikitable" style="text-align: left; width: 600px; height: 200px;"
|+ Beidou B1I signal characteristics <ref>[http://en.beidou.gov.cn/SYSTEMS/Officialdocument/201902/P020190227601370045731.pdf] Beidou B1I signal characteristics</ref>
|-
! Technical KPI
! High Level Description
|-
| Carrier Frequency || 1561.098 MHz
|-
| Modulation Mode || Binary Phase Shift Keying (BPSK)
|-
| Polarization Mode || Right-Hand Circularly Polarized (RHCP)
|-
| Carrier Phase Noise || Third-order phase locked loop with 10 Hz one-sided noise bandwidth
|-
| Received Power Levels on Ground || -163 dBW (measured at the output of a 0 dBi RHCP user receiving antenna when the satellites are above a 5-degree elevation angle)
|-
| Signal Multiplexing Mode || Code Division Multiple Access (CDMA)
|-
| Signal Bandwidth || 4.092 MHz (centered at the carrier frequency)
|-
| Spurious || Shall not exceed -50dBc
|-
| rowspan="2" |Signal Coherence || The random jitters of the ranging code phase differentials between B1I, B2I and B3I shall be less than 1ns (1σ).
|-
| The random jitter of the initial phase differential between the ranging code and the corresponding carrier shall be less than 3° (1σ).
|-
| Equipment Group Delay Differential || TGD1 (less than 1ns)
|}

== BeiDou B1C Band ==
This section defines the characteristics of the open service signal B1C transmitted by the Medium Earth Orbit (MEO) satellites and the Inclined GeoSynchronous Orbit (IGSO) satellites of BDS-3 for providing open service, and shall not be transmitted by the Geostationary Earth Orbit (GEO) satellites.
The signal characteristics described in this chapter pertain to the B1C signal contained within the 32.736 MHz bandwidth with a center frequency of 1575.42MHz.
The carrier frequencies, modulations and symbol rates of the B1C signal are shown in the following table.<ref>[http://en.beidou.gov.cn/SYSTEMS/Officialdocument/201806/P020180608525871869457.pdf] BeiDou Navigation Satellite System Signal In Space Interface Control Document Open Service Signal B1C (Version 1.0) </ref>

{| class="wikitable" style="text-align: left; width: 600px; height: 200px;"
|+ Beidou B1C components: frequencies and modulations
|-
! Signal
! Signal component
! Carrier frequency (MHz)
!Modulation
!Symbol rate (sps)
|-
| rowspan="2" | B1C
| Data component B1C_data
| rowspan="2" | 1575.42
| BOC(1,1)
| 100
|-
| Pilot component B1C_pilot
| QMBOC(6, 1, 4/33)
| 0
|}
The complex envelope of the B1C signal is expressed as: 
SB1C(t) = SB1C_data(t)+jS SB1C_pilot (t) 
Where the SB1C_data(t) is the data component, which is generated from the navigation message data DSB1C_data(t) and the ranging code CSB1C_data(t) modulated with the sine-phase BOC(1,1) subcarrier scSB1C_data(t). SB1C_pilot(t) is generated from the ranging code CB1C_pilot(t), modulated with the QMBOC(6,1,4/33) subcarrier scB1C_pilot(t). The power ratio of the data component to the pilot component is 1:3. 
In the next table appear phase relationship, as well as the power ratio of each component.
{| class="wikitable" style="text-align: left; width: 600px; height: 200px;"
|+ Beidou B1C phase relationship and power ratio per component
|-
! Component
! colspan="2" | Modulation
! Phase relationship
! Power ratio
|-
| SB1C_data(t)
| colspan="2" | Sine BOC(1,1)
| 0
| 1/4
|-
| SB1C_pilot_a (t)
| rowspan="2" | QMBOC (6,1,4/33)
| Sine BOC(1,1)
| 90
| 29/44
|-
| SB1C_pilot_b (t)
| Sine BOC(6,1)
| 0
| 1/11
|}
To conclude some technical characteristics of the BeiDou B1C signals are given bellow: 
{| class="wikitable" style="text-align: left; width: 600px; height: 200px;"
|+ Beidou B1C signal characteristics
|-
! Technical KPI
! High Level Description
|-
| Carrier Frequency || 1575.42 MHz
|-
| Modulation Mode || BOC/QMBOC
|-
| Polarization Mode || Right-Hand Circularly Polarized (RHCP)
|-
| Carrier Phase Noise || Third-order phase locked loop with 10 Hz one-sided noise bandwidth
|-
| Received Power Levels on Ground || -159 dBW for MEO and -161 dBW for IGSO satellites
|-
| Signal Multiplexing Mode || Code Division Multiple Access (CDMA)
|-
| Signal Bandwidth || 32.736 MHz (centered at the carrier frequency)
|-
| Spurious || Shall not exceed -50dBc
|-
| Signal Coherence || The time difference between the ranging code phases of all signal components <= 10 ns.
|-
| Correlation Loss || The correlation loss due to payload distortions <= 0.3 dB
|-
| rowspan="2" |Data/Code Coherence
| The edge of each data symbol is aligned with the edge of the corresponding ranging code chip. The start of the first chip of the periodic ranging codes is aligned with the start of a data symbol.
|-
| The edge of each secondary chip is aligned with the edge of a primary code chip. The start of the first chip of the primary codes is aligned with the start of a secondary code chip.
|}

== BeiDou B2a Band ==
The signal characteristics described in this point correspond to the B2a signal contained within the 20,46 MHz bandwidth with a center frequency of 1176,45 MHz. The following table shows the carrier frequencies, modulations and symbol rates of the B2a signal <ref>[http://en.beidou.gov.cn/SYSTEMS/Officialdocument/201806/P020180608525870555377.pdf] BeiDou Navigation Satellite System Signal In Space Interface Control Document Open Service Signal B2a (Version 1.0). </ref>.

{| class="wikitable" style="text-align: left; width: 600px; height: 200px;"
|+ Beidou B2a components: frequencies and modulations
|-
! Signal
! Signal component
! Carrier frequency (MHz)
!Modulation
!Symbol rate (sps)
|-
| rowspan="2" | B2a
| Data component B2a_data
| rowspan="2" | 1176.45
| rowspan="2" | BPSK(10)
| 200
|-
| Pilot component B2a_pilot
| 0
|}
Taking into account both aforementioned signal components, the complex envelope of the B2a signal is:
SB2a (t) = SB2a_data(t)+jS SB2a_pilot (t)
Where, the data component is generated from the navigation message data (DB2a_data(t)) modulated with the ranging code CB2a_data(t), while the pilot component contains the ranging code CB2a_Pilot(t) only. They both adopt BPSK(10) modulation. The power ratio of the data component to the pilot component is 1:1. 
In the next table appear phase relationship, as well as the power ratio of each component.
{| class="wikitable" style="text-align: centre; width: 600px; height: 200px;"
|+ Beidou B2a phase relationship and power ratio per component
|-
! Component
! Modulation
! Phase relationship
! Power ratio
|-
| SB2a_data(t)
| rowspan="2" | BPSK(10)
| 0
| rowspan="2" | 1/2
|-
| SB2a_pilot (t)
| 90
|}

To conclude, some technical characteristics on the BeiDou B2a signals are presented more in detail in the next table:
{| class="wikitable" style="text-align: left; width: 600px; height: 200px;"
|+ Beidou B2a signal characteristics
|-
! Technical KPI
! High Level Description
|-
| Carrier Frequency || 1176.45 MHz
|-
| Modulation Mode || Binary Phase Shift Keying (BPSK)
|-
| Polarization Mode || Right-Hand Circularly Polarized (RHCP)
|-
| Carrier Phase Noise || Third-order phase locked loop with 10 Hz one-sided noise bandwidth
|-
| Received Power Levels on Ground || -156 dBW for MEO and -158 dBW for IGSO satellites (measured at the output of a 0 dBi RHCP user receiving antenna when the satellites are above a 5-degree elevation angle)
|-
| Signal Multiplexing Mode || Code Division Multiple Access (CDMA)
|-
| Signal Bandwidth || 20.46 MHz (centered at the carrier frequency)
|-
| Spurious || Shall not exceed -50dBc
|-
| Signal Coherence || The time difference between the ranging code phases of all signal components <= 10 ns.
|-
|-
| rowspan="2" |Data/Code Coherence
| The edge of each data symbol is aligned with the edge of the corresponding ranging code chip. The start of the first chip of the periodic ranging codes is aligned with the start of a data symbol.
|-
| The edge of each secondary chip is aligned with the edge of a primary code chip. The start of the first chip of the primary codes is aligned with the start of a secondary code chip.
|}

== BeiDou B3 Band ==
Finally, this section of the document defines the characteristics of the open service signal B3I, transmitted by the BDS-2 and BDS-3 satellites including MEO, IGSO and GEO satellites for providing open service.

The B3I signal is composed of the carrier frequency, ranging code and navigation message. The ranging code and navigation message are modulated on carrier. The B3I signal is expressed as follows <ref> [http://en.beidou.gov.cn/SYSTEMS/Officialdocument/201806/P020180608525869304359.pdf] BeiDou Navigation Satellite System Signal In Space Interface Control Document Open Service Signal B3I (Version 1.0) </ref>:

SjB3I (t) = AB3ICjB3I(t)DjB3I(t)cos(2πf3t + ѰjB3I)
Where: 
• Superscript j: satellite number 
• AB3I : amplitude of B3I 
• CB3I : ranging code of B3I 
• DB3I : data modulated on ranging code of B3I 
• f3 : carrier initial frequency of B3I 
• ѰB3I : carrier initial phase of B3I 

To conclude, some technical characteristics on the BeiDou B3 signals are provided next.

{| class="wikitable" style="text-align: left; width: 600px; height: 200px;"
|+ Beidou B3I signal characteristics
|-
! Technical KPI
! High Level Description
|-
| Carrier Frequency || 1268.520 MHz
|-
| Modulation Mode || Binary Phase Shift Keying (BPSK)
|-
| Polarization Mode || Right-Hand Circularly Polarized (RHCP)
|-
| Carrier Phase Noise || Third-order phase locked loop with 10 Hz one-sided noise bandwidth
|-
| Received Power Levels on Ground || -163 dBW (measured at the output of a 0 dBi RHCP user receiving antenna when the satellites are above a 5-degree elevation angle)
|-
| Signal Multiplexing Mode || Code Division Multiple Access (CDMA)
|-
| Signal Bandwidth || 20.46 MHz (centered at the carrier frequency)
|-
| Spurious || Shall not exceed -50dBc
|-
| rowspan="2" |Signal Coherence || The random jitters of the ranging code phase differentials between B1I, B2I and B3I shall be less than 1ns (1σ).
|-
| The random jitter of the initial phase differential between the ranging code and the corresponding carrier shall be less than 3° (1σ).
|-
| Equipment Group Delay Differential || Tref (less than 0.5ns)
|}

==References==
<references/>

== Credits ==

[[Category:Fundamentals]]
[[Category:GNSS Signals]]
[[Category:BEIDOU]]

BeiDou Services

2026-04-17T14:20:27Z

Gema.Cueto: Updated reference ICD/SDD links

BeiDou Receivers

2026-04-17T14:14:58Z

Gema.Cueto: Updated reference ICD/SDD links

BeiDou Future and Evolutions

2026-04-17T14:11:48Z

Gema.Cueto: Updated reference ICD/SDD links

{{Article Infobox2
|Category=BEIDOU
|Editors=GMV
|Level=Basic
|YearOfPublication=2011
|Logo=GMV
|Title={{PAGENAME}}
}}
The [[BeiDou_General_Introduction|BeiDou Navigation Satellite System (BDS)]], also known as BeiDou-2<ref name=BDS_STATUS> Compass/BeiDou Status, Jun Shen, BNStar Navigation Technology & System, Inc., Rome (Italy), June 11, 2009</ref>, is China’s second-generation satellite navigation system<ref name=BDS_STATUS/><ref>[https://en.wikipedia.org/wiki/Beidou_Navigation_Satellite_System BeiDou Navigation Satellite System in Wikipedia]</ref> that will be capable of providing positioning, navigation, and timing services to users on a continuous worldwide basis<ref name=BDS_WORLDWIDE> BeiDou China’s Rapidly Emerging GNSS, InsideGNSS, May/June 2014</ref>.

==BeiDou Roadmap==

The BeiDou system is planned to be developed and deployed in three phases<ref>[http://www.beidou.gov.cn/2010/05/19/20100519101180c595f14a6d9938a42a2d796b56.html|Official BeiDou web site]</ref>:

* Phase 1 (2003+)
:Phase 1 consists of an experimental regional navigation system, BeiDou-1, which provided active navigation service.

* Phase 2 (2012+)
:BeiDou-2 consists of a reduced satellite constellation and provides open service over China. This phase aims at deploying a system with passive positioning and timing capability over a regional area.

* Phase 3 (2020+)
:By 2020, BeiDou would reach full operational capability with a Walker constellation of 27 MEOs plus 5 GEOs and the existing 3 IGSOs satellites of the regional system<ref name=BDS_STATUS/>. BeiDou would provide global navigation services, similarly to the [[GPS General Introduction|GPS]], [[GLONASS General Introduction|GLONASS]] or [[GALILEO General Introduction|Galileo]] systems.<ref name=BDS_STATUS/>

==BeiDou Status==

By December 2011, the BeiDou system went into operation on a trial basis providing initial passive positioning navigation and timing services for the whole Asia-Pacific region with a constellation of 10 satellites (5 GEO satellites and 5 IGSO satellites)<ref name="China Daily">[http://europe.chinadaily.com.cn/business/2011-12/28/content_14343656.htm Satellite navigation system launched], China Daily Europe, December 2011.</ref><ref>[[Wikipedia:Beidou Navigation Satellite System|Beidou Navigation Satellite System in Wikipedia]]</ref> and the Initial Operational Service was declared officially available.

During 2012, four launches were made in February, April, September and October, placing in orbit two adittional GEO and four MEO satellites in-line with the objective of expanding the service area to Asian-Pacific users and improving service performance (positioning accuracy better than 10 meters)<ref name=BEIDOU_MUNICH_2011>China Satellite Navigation Office, Development of BeiDou Navigation Satellite System, Munich Satellite Navigation Summit, 2011</ref>. The constellation is currently composed by 6 GEO + 5 IGSO + 4 MEO which corresponds to 15 operational satellites of the 35 planned.
Furthermore, the first version of the [http://en.beidou.gov.cn/SYSTEMS/ICD/201902/P020190227702348791891.pdf SIS ICD for the BeiDou B1I open service signal] was released on the 27th December 2012 at a news conference held in Beijing by the Chinese State Council Information Office<ref>http://www.gpsworld.com/beidou-icd-released GPS World January 2013</ref>, where it was also announced that the english name of the system was now to be replaced with BeiDou Navigation Satellite System, instead of its translation, BeiDou.

On March 30, 2015, the China Satellite Navigation Office (CSNO) announced the successful launch of the first New-Generation BeiDou Satellite. This is the 17th satellite for the BeiDou Navigation Satellite System (BDS) that marks the beginning of expanding the regional BDS to global coverage, scheduled to be fully deployed by 2020<ref>[http://insidegnss.com/china-launches-new-generation-beidou-satellite/ China Launches New-Generation BeiDou Satellite], Inside GNSS, March 31, 2015</ref>.

On July 25, 2015, China launched two new satellites (18th and 19th) for the nation’s Beidou Navigation Satellite System. The spacecraft will be used to test the new BeiDou Phase III navigation signal and inter-satellite links. China will migrate its B1 open civil signal from 1561.098 MHz to a frequency centered at 1572.42. The signal modulation will also change from a quadrature phase shift keying (QPSKZ) modulation to a multiplexed binary offset carrier (MBOC).<ref>[http://insidegnss.com/china-launches-pair-of-new-generation-beidou-gnss-satellites/ China Launches Pair of New-Generation BeiDou GNSS Satellites], Inside GNSS, July 26 2015</ref>.
The two new satellites have begun operating and established inter-satellite links in the Beidou constellation on August 14, 2015.<ref>[http://insidegnss.com/chinas-new-beidou-gnss-satellites-come-on-line-talk-to-each-other/ China's New BeiDou GNSS Satellites Come on Line, Talk to Each Other], Inside GNSS, August 16 2015</ref>. Signals from those two last satellites were acquired at Ispra, Italy, in early August.<ref>[http://gpsworld.com/first-signals-of-beidou-phase-3-acquired-at-ispra-italy/ First Signals of BeiDou Phase 3 Acquired at Ispra, Italy], GPS World, August 21, 2015</ref> 

On September 30, 2015, China has launched the 20th BeiDou satellite, with a series of tests related to the clock and a new Phase III navigation signal currently being undertaken, according to a statement from the China Satellite Navigation Office.<ref>[http://insidegnss.com/china-launches-20th-beidou-satellite/ China Launches 20th BeiDou Satellite]</ref> In October, this last satellite started broadcasting a signal similar to the future GPS L1C signal with time-division BOC(1,1) and BOC(6,1) signals.<ref>[http://gpsworld.com/new-beidou-tmboc-signal-tracked-similar-to-future-gps-l1c-structure/ New BeiDou TMBOC Signal Tracked; Similar to Future GPS L1C Structure]</ref> 
On February 1, 2016, China has launched the first Beidou satellite of the year, also part of the Beidou Phase III,<ref>[http://insidegnss.com/china-launches-new-meo-beidou-satellite-18-more-to-come-by-end-of-2018/ China Launches New MEO BeiDou Satellite; 18 More to Come by End of 2018]</ref> with the 2nd of the year (the 22nd Beidou satellite) following closely with its launch on March 29, 2016.<ref>[http://gpsworld.com/china-launches-22nd-beidou-satellite/ China launches 22nd BeiDou satellite]</ref> 
The 23rd Beidou satellite was launched on June 12, 2016.<ref>[http://insidegnss.com/china-launches-another-beidou-navigation-satellite/ CChina Places 23rd BeiDou Satellite into Orbit]</ref> 

==BeiDou General Services==

The future BeiDou is expected to support two different kind of [[BeiDou_Services|general services]]: RDSS and RNSS.

In the Radio Determination Satellite Service (RDSS) , the user position is computed by a ground station using the round trip time of signals exchanged via GEO satellite. The RDSS Long term feature further includes<ref>"Preliminary Results of GPS/BeiDou Integrated Positioning and Navigation", presented in the BeiDou Workshop held during the ION GNSS 2011 Conference.</ref>:
* Short message communication (guaranteeing backward compatibility with BeiDou-1)
* Large volume message communication
* Information connection
* Extended coverage

The Radio Navigation Satellite Service (RNSS) is very similar to that provided by GPS and Galileo and is designed to achieve similar performances.

More information regarding Beidou services can be found in the [http://en.beidou.gov.cn/SYSTEMS/ICD/index.html BeiDou Navigation Satellite System Signal In Space Interface Control Document]

==International Context==

The Chinese Government considers satellite navigation as strategic in the new generation information technology, and encourages international cooperation to ensure [[Principles_of_Compatibility_among_GNSS|compatibility]] and [[Principles_of_Interoperability_among_GNSS|interoperability]] with other navigation systems<ref name=BEIDOU_MUNICH_2011>China Satellite Navigation Office, Development of BeiDou Navigation Satellite System, Munich Satellite Navigation Summit, 2011</ref>.

==References==
<references/>

[[Category:BEIDOU]]

GLONASS User Segment

2026-04-17T14:04:39Z

Gema.Cueto: Updated reference ICD/SDD links

{{Article Infobox2
|Category=GLONASS
|Editors=GMV
|Level=Basic
|YearOfPublication=2011
|Logo=GMV
|Title={{PAGENAME}}
}}
The GLONASS User Segment consists on L-band radio receiver/processors and antennas which receive GLONASS signals, determine pseudoranges (and other observables), and [[An intuitive approach to the GNSS positioning|solve the navigation equations]] in order to obtain their coordinates and provide a very accurate time.

==GLONASS Receivers==
A [[GLONASS Receivers|GLONASS Receiver]] is a device capable of determining the user position, velocity and precise time (PVT) by processing the signal broadcasted by satellites.

Any navigation solution provided by a [[GNSS Receivers General Introduction|GNSS Receiver]] is based on the computation of its distance to a set of satellites, by means of extracting the propagation time of the incoming signals traveling through space at the speed of light, according to the satellite and receiver local clocks.

Notice that satellites are always in motion, so previous to obtaining the navigation message, the satellite’s signal is detected and tracked. The receiver’s functional blocks that perform these tasks are the antenna, the front-end and the baseband signal processing (in charge of acquiring and tracking the signal).

Once the signal is acquired and tracked, the receiver application decodes the navigation message and estimates the user position. The Navigation Message includes:<ref name="GNSS-Book ">J. Sanz Subirana, JM. Juan Zornoza and M. Hernández-Pajares, ''Global Navigation Satellite Systems: Volume I: Fundamentals and Algorithms''</ref>
* Ephemeris parameters, needed to compute the satellite’s coordinates
* Time parameters and Clock Corrections, to compute satellite clock offsets and time conversions
* Service Parameters with satellite health information
* Almanacs, needed for the acquisition of the signal by the receiver. It allows computing the position of all satellites but with a lower accuracy than the ephemeris

The ephemeris and clocks parameters are usually updated every half-an-hour, whereas the almanac is updated at least every six days.

For more information, please refer to GLONASS Interface Control Document <ref name="ICD-GLONASS-eng">[https://unavco.knowledgebase.co/assets/727/ikd51en.pdf GLONASS Interface Control Document, Edition 5.1]</ref> which specifies parameters of interface between GLONASS space segment and user equipment in L1 and L2 Bands

==Commercial use==
Although the GLONASS constellation is nearing global coverage, its commercialization, especially development of the user segment, has been lacking compared to the U.S. GPS system.<ref name="GLONASS_Wikipedia">[http://en.wikipedia.org/wiki/GLONASS GLONASS on Wikipedia]</ref>

To improve the situation, the Russian government has been actively promoting GLONASS for civilian use. In 2001, the government announced that all passenger cars, large transport vehicles and vehicles transporting dangerous materials were required to use GLONASS-equipped navigators.<ref name=RUSSIA_ACEL>[http://asmmag.com/2012-12-30-14-40-18/feature/1472-russia-accelerates-glonass-navigation-satellite-launches.html Russia Accelerates GLONASS Navigation Satellite Launches]</ref> The tracking of this road traffic will be tied to road tax collection as well as to a roadside assistance in the event of an accident.<ref name=RUSSIA_ACEL/>
In addition, the government has been pushing for all car manufacturers in Russia to make cars with GLONASS since 2011. This affects all car makers, including foreign brands like Ford and Toyota, which have car assembling facilities in Russia.<ref name="GLONASS_Wikipedia"/>

Commercial response to GLONASS improved accuracy las lead to several recent announcements that include:
* Qualcomm has announced the first GLONASS capable phone (MTS 945 from ZTE): "ZTE is first to market with a smartphone that supports both the GPS and GLONASS satellite systems, taking full advantage of the functionality which has been integrated into our Snapdragon MSM7x30 chipset and software”.<ref>[http://www.glonass-center.ru/en/content/news/?ELEMENT_ID=116 Qualcomm Incorporated now has product support for the Russian GLONASS satellite system]></ref>
*On February 2, ST-Ericsson launched “the world’s smallest receiver” to connect to both GPS and GLONASS satellites.<ref>[http://gpsworld.com/ ST-Ericsson Launches GPS + GLONASS Receiver]</ref>
* Broadcom Corporation, a global leader in semiconductors for wired and wireless communications, announced two new GPS system-on-a-chip solutions that include support for the GLONASS Russian Navigation Satellite System.<ref>[http://www.broadcom.com/press/release.php?id=s548713 Broadcom announces two new system-on-a-chip solutions with support for GLONASS]</ref>
*In April 2011, Sweden’s Swepos became the first foreign company to use Russia’s GLONASS positioning technology, due to Swepos’ conviction that it is better than GPS at northern latitudes.<ref>[http://www.ewdn.com/2011/04/12/swedish-satellite-data-provider-prefers-glonass-to-gps/ Swedish satellite data provider prefers GLONASS to GPS]</ref>

==Applications==
[[File:app_survey.jpg|200px|thumb|right]]
[[File:app_transport.png|250px|thumb|right]]
[[GNSS Applications|GLONASS applications]] are all those applications that use GLONASS to collect position, velocity and time information to be used by the application.
Global navigation and time synchronization service of unlimited number of users on ground, on sea, airborne and in space:<ref>[http://www.spacecorp.ru/en/directions/glonass/function/ GLONASS Applications on spacecorp.ru]</ref>
* Armed Forces
* Communication and energy systems synchronization
* Geodesy: GLONASS and GLONASS\GPS receivers are used to determine precise coordinates of points and land parcel boundaries
* Cartography: GLONASS is used in civilian and military cartography
* Tectonics: tectonic plates movements and convulsions are tracked using satellites
* Navigation: global positioning systems are used for maritime and roadway navigation
* Satellite monitoring: ERA-GLONASS project is motor vehicle position and velocity monitoring and control over their movements
* Complex engineering structures monitoring
* Animals monitoring, environmental protection
* Search and rescue facilitation
* Personal trackers, "panic button"

==Notes==
<references group="footnotes"/>
==References==
<references/>

[[Category:GLONASS]]

GLONASS Services

2026-04-17T13:59:43Z

Gema.Cueto: Updated reference ICD/SDD links

{{Article Infobox2
|Category=GLONASS
|Editors=GMV
|Level=Basic
|YearOfPublication=2011
|Logo=GMV
|Title={{PAGENAME}}
}}
Equivalent to the Standard Positioning Service (SPS) and the Precise Positioning Service (PPS) of GPS, GLONASS provides a standard precision (SP) navigation signal and a high precision (HP) navigation signal, namely the Channel of Standard Accuracy (CSA) and Channel of High Accuracy (CHA), respectively.

==Standard Precision Service (SP)==

Originally, the Standard Precision signal was transmitted only on L1, whereas the High Accuracy code was transmitted both on L1 and L2. The modernization of GLONASS began with the launch of second generation of satellites, GLONASS-M. Since that moment on, a second civil signal on L2 band is transmitted, allowing user to cancel out the ionospheric refraction.
Currently, with the first GLONASS-K sent into orbit, a third civil signal on L3 band is available for civilian users (for more information, please refer to [[GLONASS Space Segment| GLONASS Space Segment]]).

The Standard Precision signals are generated by the Modulo-2 addition of the following three binary signals:
* PR ranging code transmitted at 511 kbps.
* Navigation message transmitted at 50 bps, and 100 Hz auxiliary meander sequence.
Given sequences are used for modulation of carriers in L1 and L2 sub-bands when generating standard accuracy signals.
PR ranging code is a sequence of maximum length of shift register with a period 1 millisecond and bit rate 511 kbps. PR ranging code is sampled at the output of 7th stage of the 9-stage shift register. The initialization vector to generate this sequence is (111111111). The first character of the PR ranging code is the first character in the group 111111100, and it is repeated every 1 millisecond. The generating polynomial, which corresponds to the 9-stage shift register, is G(X) = 1 + X5 + X9.<ref name="ICD-GLONASS-eng">[https://unavco.knowledgebase.co/assets/727/ikd51en.pdf Interface Control Document, Edition 5.1]</ref>

==High Precision Service (HP)==
The High Precision signal is broadcast in phase quadrature with the SP signal, effectively sharing the same carrier wave as the SP signal, but with a ten times higher bandwidth (5.11 Mbps) than the SP signal.<ref>[http://en.wikipedia.org/wiki/GLONASS GLONASS on Wikipedia]</ref>
GLONASS is not degraded artiﬁcially by the system operators. Neither there are plans to introduce such measures in future.

The GLONASS P-code never was published by the system operators, but it was made known to the scientific community. This means, the GLONASS P-code is fully available. However, along with the P-code not being published by the system operators, it neither was officially released for use outside the Russian Armed Forces. Instead, they reserve the right to alter the code in future. This keeps a number of potential users and receiver manufacturers from actually implementing the GLONASS P-code.<ref name="rossbach-udo">[http://d-nb.info/969738064/34 Positioning and Navigation Using the Russian Satellite System GLONASS, Udo Roßbac]</ref>

==Military Signal Access to India==
In January 2004 the Russian Space Agency (RSA) announced a deal with India's space agency, wherein the two government agencies would collaborate to restore GLONASS system to constant coverage of Russian and Indian territory by 2008 with 18 satellites, and be fully operational with all 24 satellites by 2010.<ref>[http://www.flightglobal.com/articles/2004/12/14/191325/india-and-russia-to-revive-glonass.html The Indian and Russian governments have reached agreement to co-operate on Glonass]</ref>

During a December 2005 summit between Indian Prime Minister Manmohan Singh and Russian President Vladimir Putin, it was agreed that India would share some of the development costs of the GLONASS-K series and launch two of the new satellites from India, in return for access to the HP signal. On December 21, 2010, during the visit of Russian President Dmitry Medvedev to India, Russia and India signed an agreement to share high precision signals from the Global Navigation Satellite System (GLONASS). <ref>[http://www.indiapost.com/russia-india-ink-agreement-to-share-glonass-signals/ Russia, India ink agreement to share GLONASS signals]</ref> India is the first country that has been given access to the GLONASS military signal.

==Notes==
<references group="footnotes"/>
==References==
<references/>

[[Category:GLONASS]]

GLONASS Navigation Message

2026-04-17T13:11:07Z

Gema.Cueto: Updated reference ICD/SDD links

{{Article Infobox2
|Category=Fundamentals
|Authors=J. Sanz Subirana, JM. Juan Zornoza and M. Hernandez-Pajares, University of Catalunia, Spain.
|Level=Basic
|YearOfPublication=2011
|Title={{PAGENAME}}
}}
GLONASS satellites modulate two navigation messages at 50 bps onto the standard (C/A) and high accuracy (P) signals, each message providing the users the necessary information for positioning (parameters to compute GLONASS satellites coordinates, their clock offsets, and various other system parameters).

The navigation message of the standard accuracy signal (C/A) is broadcast as continuously repeating superframes with a duration of 2.5 minutes. Each superframe consists of 5 frames of 30 seconds, and each frame consists of 15 strings of 2 seconds duration (100 bits length).

[[File:GLONASS navigation message structure.png|none|thumb|400px|alt=GLONASS navigation message structure|'''''Figure 2:''''' GLONASS navigation message structure (source GLONASS-ICD).]]

The message content divides the data in immediate data of the transmitting satellite and non-immediate data for the other satellites. The immediate data is repeated in the first four strings of every frame. It comprises the ephemeris parameters, satellite clock offsets, satellite healthy flag and the relative difference between carrier frequency of the satellite and its nominal value. The non-immediate data is broadcast in the strings 5 to 15 of each frame (almanac for 24 satellites). The frames I to IV contain almanac for 20 satellites (5 per frame), and the 5th frame almanac for 4 satellites. The last 2 strings of frame 5 are reserved bits (the almanac of each satellite uses 2 strings).

The ephemerides values are predicted from the Ground Control Centre for a 24 hours period, and the satellite transmits a new set of ephemerides every 30 minutes. These data differ from GPS data. Instead of Keplerian orbital elements, they are provided as Earth Centred Earth Fixed (ECEF) Cartesian coordinates in position and velocity, with lunisolar acceleration perturbation parameters. The GLONASS-ICD <ref>[https://unavco.knowledgebase.co/assets/727/ikd51en.pdf GLONASS ICD]</ref> provides the integration equations based on 4th-order-Runge-Kutta method, which includes the second zonal geopotential harmonic coefficient. The almanac is quite similar to the GPS one, given as modified Keplerian parameters, and it is updated approximately once per day.

The navigation message of the high accuracy signal (P) structure is not officially published, but different research groups decoded it. According with these investigations each satellite transmits a superframe, which is composed of 72 frames, each containing 5 strings of 100 bits. A frame needs 10 seconds to be transmitted, thence the total length of message is 12 minutes. The first three frames contain the ephemeris for the transmitting satellite.

==Notes==
<references group="footnotes"/>

==References==
* Hofmann-Wellenhof, B., Lichtenegger, H., K. and Wasle, E., 2008. GNSS - Global Navigation Satellite Systems.. Springer-Verlag, Wien, Austria.
* [http://www.oosa.unvienna.org/pdf/publications/st_space_24E.pdf United Nations, 2004] Report of the action team on global navigation satellite systems (GNSS) – Follow up to the Third United Nations Conference on the Exploration and Peaceful Uses of Outer Space (UNISPACE III).

[[Category:Fundamentals]]
[[Category:GLONASS]]
[[Category:GLONASS Signal Structure]]

GLONASS General Introduction

2026-04-17T13:03:29Z

Gema.Cueto: Updated reference ICD/SDD links

{{Article Infobox2
|Category=GLONASS
|Editors=GMV
|Level=Basic
|YearOfPublication=2011
|Logo=GMV
|Title={{PAGENAME}}
}}
[[:Category:GLONASS|GLONASS]] is a space-based global navigation satellite system (GNSS) that provides reliable positioning, navigation, and timing services to users on a continuous worldwide basis freely available to all. GLONASS receivers compute their position in the [[Glonass Reference Frame|GLONASS Reference System]] using satellite technology and based on [[An intuitive approach to the GNSS positioning|triangulation principles]]. It is an alternative and complementary to other GNSS systems such as the United States' Global Positioning System ([[GPS General Introduction|GPS]]), the Chinese [[BeiDou General Introduction|BeiDou]] navigation system or the planned [[GALILEO General Introduction|Galileo]] positioning system of the European Union (EU).

==Introduction==
The first Soviet navigation spacecraft “Cyclone” was launched into orbit in 1967.<ref name="History_IAC">[http://new.glonass-iac.ru/en/guide/ GLONASS History on Information-analytical centre ]</ref> This was the beginning of the first Soviet low orbit navigation system, called “Cicada”. It was composed of four satellites placed in circular orbits at an altitude of 1000 km and an inclination of 83 deg and could provide positioning data within the limits of several hundred meters. Nevertheless the requirements to space navigation were constantly increasing and low-orbit systems could not comply with the requirements of all potential users.

Flight tests of high altitude (20000 km) satellite navigation system, called [[:Category:GLONASS|GLONASS]] were started in 12 October 1982 with the launch of the Kosmos-1413, Kosmos-1414, and Kosmos-1415<ref name="History_IAC"/>. After the dissolution of the Soviet Union in 1991, the system was continued by the Russian Federation which formally declared the system operational in 1993 <ref name="PutinAnnouncement">[http://en.rian.ru/science/20070518/65725503.html Announcement of Putin making GLONASS free for customers] </ref> and brought to its optimal status of 24 operational satellites in 1995.

Following completion, the system fell into disrepair with the collapse of the Russian economy and the reduction in funding for space industry <ref>[[Wikipedia:History_of_GLONASS|GLONASS History on wikipedia]]</ref>. In the early 2000s, under Vladimir Putin's presidency, the restoration of the system was made a top government priority and funding was substantially increased. In May 2007 Russian President Vladimir Putin signed a decree on the [[:Category:GLONASS|GLONASS]] navigation system to provide the service free for customers: "Access to civilian navigation signals of global navigation satellite system [[:Category:GLONASS|GLONASS]] is provided to Russian and foreign consumers free of charge and without limitations".<ref name="PutinAnnouncement"/>

==GLONASS Signal Structure==
[[File:GlonassSignalStructure.JPG|GLONASS Signal Spectrum|400px|thumb|right]]
Each [[:Category:GLONASS|GLONASS]] system Space Vehicle (SV) "GLONASS" and "GLONASS-M" transmits navigational radiosignals on fundamental frequencies in two frequency sub-bands (L1 ~ 1,6 GHz, L2 ~ 1,25 GHz).<ref name="ICD-GLONASS-eng">[https://unavco.knowledgebase.co/assets/727/ikd51en.pdf GLONASS Interface Control Document, Edition 5.1]</ref>

It is important to remark that [[:Category:GLONASS|GLONASS]] relies on the Frequency Division Multiple Access (FDMA) technique instead of the CDMA one used by other GNSS systems such [[GPS General Introduction|GPS]] or [[GALILEO General Introduction|GALILEO]]. Each satellite transmits navigation signals on its own carrier frequency, so that two [[:Category:GLONASS|GLONASS]] satellites may transmit navigation signals on the same carrier frequency if they are located in antipodal slots of a single orbital plane.<ref name="ICD-GLONASS-eng"/>

The frequency of transmission of each [[:Category:GLONASS|GLONASS]] satellite can be derived from the channel number k<ref name="GLONASSConstellationStatus">[http://www.glonass-center.ru/en/GLONASS GLONASS Constellation Status, Information Analytical Centre, Russian Federal Space Agency]</ref> by applying the following expressions:<ref name="ICD-GLONASS-eng"/>
*<math>f_{k1} =f_{01} + k\Delta f_1</math>, where <math>f_{01} =1602 MHz</math> and <math>\Delta f_1=562.5 KHz</math>
*<math>f_{k2} =f_{02} + k\Delta f_2</math>, where <math>f_{02} =1246 MHz</math> and <math>\Delta f_2=437.5 KHz</math>

The modernization of [[:Category:GLONASS|GLONASS]] will add a new third frequency G3 in the ARNS band for the GLONASS-K satellites. This signal will provide a third civil C/A2 and military P2 codes, being especially suitable for Safety-Of-Life applications.

==GLONASS Reference Frame==
Accurate and well-defined Time References and Coordinate Frames are essential in GNSS, where positions are computed from signal travel time measurements and provided as a set of coordinates (please refer to [[An intuitive approach to the GNSS positioning|GNSS positioning]]). [[:Category:GLONASS|GLONASS]] time (GLONASST) is generated by the GLONASS Central Synchroniser (CS). Unlike GPS, the GLONASS time scale is adjusted for periodic leap seconds and the difference between the UTC (Coordinated Universal Time) and GLONASST should not exceed 1 millisecond plus three hours.<ref name="ICD-GLONASS-eng"/>

As specified in the ''GLONASS Interface Control Document'', the [[:Category:GLONASS|GLONASS]] broadcast ephemeris describes a position of transmitting antenna phase center of given satellite in the PZ-90.02 Earth-Centered Earth-Fixed reference frame defined as follows:<ref name="ICD-GLONASS-eng"/>
* The ORIGIN is located at the center of the Earth's body.
* The Z-axis is directed to the Conventional Terrestrial Pole as recommended by the International Earth Rotation Service (IERS).<ref>[https://www.iers.org/IERS/EN/Home/home_node.html Earth Rotation Service (IERS)]</ref>
* The X-axis is directed to the point of intersection of the Earth's equatorial plane and the zero meridian established by the Bureau International de l'Heure (BIH).
* The Y-axis completes the coordinate system to the right-handed on.

==GLONASS Services==
Two services are available from [[:Category:GLONASS|GLONASS]] system:<ref>J. Sanz Subirana, JM. Juan Zornoza and M. Hernández-Pajares, Global Navigation Satellite Systems: Volume I: Fundamentals and Algorithms</ref>
* SPS: The Standard Positioning Service (or Standard Accuracy Signal service) is an open service, free of charge for worldwide users. The navigation signal was initially provided only in the frequency band G1, but from 2004 on the new GLONASS-M transmits also a second civil signal in G2.
* PPS: The Precise Positioning Service (or High Accuracy Signal service) is restricted to military and authorized users. Two navigation signals are provided in the two frequency bands G1 and G2.

==GLONASS Architecture==
[[:Category:GLONASS|GLONASS]] is comprised of three segments: a [[GLONASS Space Segment|GLONASS Space Segment]] (SS), a [[GLONASS Ground Segment|GLONASS Ground Segment]] (CS), and a [[GLONASS User Segment|GLONASS User Segment]] (US)<ref name="ICD-GLONASS-eng"/>.

According to the GLONASS Interface Control Document,<ref name="ICD-GLONASS-eng"/> the [[GLONASS Space Segment| GLONASS Space Segment]] ''is composed of 24 satellites in three orbital planes whose ascending nodes are 120 deg apart. Eight satellites are equally spaced in each plane with argument of latitude displacement of 45 deg<ref name="SDCM">[http://www.sdcm.ru/index_eng.html Russian System of Differentional Correction and Monitoring]</ref>. The satellites operate in circular orbits at an altitude of 19100-km, an inclination of 64.8 deg and each satellite completes the orbit in approximately 11 hours 15 minutes. The spacing of the satellites allows providing continuous and global coverage of the terrestrial surface and the near-earth space.''

[[GLONASS Ground Segment| GLONASS Ground Segment]] ''includes the System Control Center and the network of the Command and Tracking Stations that are located throughout the territory of Russia. The control segment provides monitoring of [[:Category:GLONASS|GLONASS]] constellation status, correction to the orbital parameters and navigation data uploading.''

Finally, [[GLONASS User Segment| GLONASS User Segment]] ''consists in the user receivers which compute coordinates, velocity and time from the [[:Category:GLONASS|GLONASS]] navigation signals.''

==GLONASS Performances==
In 2006, when the Defence Minister Sergey Ivanov ordered that one of the existing GLONASS signals was made available to the civilian users the achievable performance was only about 30 meters. However, there was another signal (encrypted signal for military purposes) which allowed to obtain a better performance and later on 2007 the president Vladimir Putting has demanded that the whole system was made available for everyone. Thus, on 18 May 2007 the achievable performance was increased to about 10 metters being yet quiete worse than the GPS performance. Since then several improvements were made on the system and currently both [[GLONASS Performances|GLONASS Performances]] and [[GPS Performances|GPS Performances]] are very similar.

==GLONASS Future and Evolutions==
[[File:K_model_at_Cebit_2011_Satellite.jpg|Glonass K satellite at the CeBIT 2011 Expo in Germany|100px|thumb|right]]
[[:Category:GLONASS|GLONASS]] modernization began with the launch of second generation of satellites, known as GLONASS-M, in 2003. The following generation of satellites, GLONASS-K, has a service life of 10 years and includes, for the first time, code-division-multiple-access (CDMA) signals in addition to the legacy FDMA signals.<ref name=GPSWLDA>[http://gpsworld.com/innovation-glonass-11405/ Innovation: GLONASS, Yuri Urlichich, Valeriy Subbotin, Grigory Stupak, Vyacheslav Dvorkin, Alexander Povalyaev, Sergey Karutin, April 1, 2011, GPS World]</ref>

[[GLONASS_Future_and_Evolutions|Evolutions of GLONASS]] are planned and in place for short, mid and long terms.

==Notes==
<references group="footnotes"/>
==References==
<references/>

[[Category:GLONASS|!]]

GPS Signal Plan

2026-04-17T12:55:54Z

Gema.Cueto: Updated reference ICD/SDD links

{{Article Infobox2
|Category=GPS
|Authors=J.A Ávila Rodríguez, University FAF Munich, Germany.
|Level=Advanced
|YearOfPublication=2011
|Title={{PAGENAME}}
}}
== GPS L1 Band ==

The GPS L1 band (1575.42 MHz) has turned to be the most important band for navigation purposes. Indeed most of the applications in the world nowadays are based on the signals transmitted at this frequency. Three signals are transmitted at the moment by GPS in L1: C/A Code, P(Y) Code,M-Code and the new L1C signal, which is in the process of being fielded as L2C and L5. The legacy civil signal, called L1 C/A or C/A at L1, will continue broadcasting in the future. We describe all of these signals modulated in the L1 RF carrier frequency in the next lines:

* The Coarse/Acquisition (C/A) code signal was primarily thought for acquisition of the P (or Y) code and has become nowadays the most important signal for mass market applications. The PRN C/A Code for SV ID number i is a Gold code, <math>G_i (t) </math>, of 1 millisecond in length at a chipping rate of 1.023 Mbps. The <math>G_i (t) </math> sequence is a linear pattern generated by the Modulo-2 addition of two subsequences, <math>G_1</math> and <math>G_{1i}</math>, each of them being a 1023 chip long linear pattern. The epochs of the Gold code are synchronized with the <math>X_1</math> epochs of the P-code.

* The P Code is the precision signal and is coded by the precision code. Moreover the Y-Code is used in place of the P-code whenever the Anti-Spoofing (A/S) mode of operation is activated as described in the ICDs 203, 224 and 225. The PRN P-code for SV number i is a ranging code, Pi(t), 7 days long at a chipping rate of 10.23 Mbps. The 7 day sequence is the Modulo-2 sum of two sub-sequences referred to as <math>X_1</math> and <math>X_{2i}</math> with 15,345,000 chips and 15,345,037 chips, respectively. The <math>X_{2i}</math> sequence is an <math>X_2</math> sequence selectively delayed by 1 to 37 chips allowing the basic code generation technique to produce a set of 37 mutually exclusive P-code sequences 7 days long.

* The modernized military signal (M-Code) is designed exclusively for military use and is intended to eventually replace the P(Y) code [E. D. Kaplan and C. Hegarty, 2006]<ref>[E. D. Kaplan and C. Hegarty, 2006] E. D. Kaplan and C. Hegarty, Understanding GPS: Principles and Applications-2nd Edition, Chapter 4.</ref>. The M-Code provides better jamming resistance than the P(Y) signal, primarily through enabling transmission at much higher power without interference with C/A code or P(Y) code receivers [B.C. Barker et al., 2000]<ref>[B.C. Barker et al., 2000] B.C. Barker, J.W. Betz, J.E. Clark, J.T. Correia, J.T. Gillis, S. Lazar, Lt. K. A. Rehborn, J.R. Straton, III, ARINC, Overview of the GPS M-Code Signal, Proceedings of the National Technical Meeting of the Institute of Navigation, ION-NTM 2000, 26-28 January 2000, Anaheim, California, USA.</ref>. Moreover, the M-Code provides more robust signal acquisition than is achieved today, while offering better security in terms of exclusivity, [[GNSS Authentication and encryption | authentication]], and confidentiality, along with streamlined key distribution. In other aspects, the M-Code signal provides much better performance than the P(Y) Code and more flexibility.

* The new L1 Civil signal (L1C), defined in the [GPS ICD-800]<ref name="GPS_SIS_ICD_800">[https://archive.gps.gov/technical/icwg/IRN-IS-800J-003.pdf GPS ICD-800 "Navstar GPS Space Segment/User Segment L1C Interfaces"]</ref>, has been designed for interoperability with Galileo E1. It is compatible with current L1 signal but broadcast at a higher power level and includes advanced design for enhanced performance. It consists of two main components; one denoted <math>L1C_P</math> to represent the pilot signal, consisting of a time-multiplexing of BOC(1,1) and BOC(6,1), thus without any data message, and <math>L1C_D</math>, with a pure BOC(1,1), for the data channel. This is spread by a ranging code and modulated by a data message. The pilot channel <math>L1C_P</math> is also modulated by an SV unique overlay secondary code, <math>L1C_O</math>. An enhancement to this L1C signal is being analysed, which is called CHIMERA (Chips Message Robust Authentication). This technique consists on adding encrypted watermarks to the L1C signal that not only let users know when a signal is being spoofed but also makes it possible to [[GNSS Authentication and encryption | authenticate]] the location of a GPS receiver to another party.

For more details on the code generation refer to the [GPS ICD 200]<ref name="GPS_SIS_ICD_200">[https://archive.gps.gov/technical/icwg/IRN-IS-200N-003.pdf GPS ICD-200 "Navstar GPS Space Segment/User Segment Interfaces"]</ref> and [GPS ICD-800]<ref name="GPS_SIS_ICD_800"></ref>. Finally, the technical characteristics of the existing GPS signals in the L1 band are summarized in the following Table 1.

::::[[File:Chapter_2_Table_1.png|none|thumb|520px|'''''Table 1:''''' GPS L1 signal technical characteristics.]]

Of all the signals above, the C/A Code is the best known as most of the receivers that have been built until today are based on it. The C/A Code was open from the very beginning to all users, although until May 1st, 2000 an artificial degradation was introduced by means of the Select Availability (SA) mechanism which added an intentional distortion to degrade the positioning quality of the signal to non-desired users. As we have already mentioned, the C/A Code was thought to be an aid for the P(Y) Code (to realize a Coarse Acquisition). The M-Code is the last military signal that has been introduced in GPS.

For a long time different signal structures for the M-Code were under consideration [J.W. Betz, 2001] <ref>[J.W. Betz, 2001a] J.W. Betz, Binary Offset Carrier Modulations for Radionavigation, NAVIGATION: Journal of The Institute of Navigation Vol. 48, No. 4, Winter 2001/02</ref>being the Manchester code signals (BPSK) and the binary offset carrier (BOC) signals the two favored candidates. Both solutions result from the modulation of a non-return to zero (NRZ) pseudo random noise spreading code by a square-wave sub-carrier. While the Manchester code has a spreading code of rate equal to that of the square-wave, the BOC signal does not necessarily have to be so, being the only constraint that the rate of the spreading code must be less than the sub-carrier frequency.

The interesting aspect about these signals is that, like the conventional sub-carrier modulation, the waveform presents a zero at the carrier frequency due to the square-wave sub-carrier. In fact, their split-power spectra clearly facilitate the compatibility of the GPS military M-Code signal with the existing C/A Code and P(Y) Code.

::::[[File:Chapter_2_Spectra_GPS_Signals_L1.png|none|thumb|520px|'''''Figure 1:''''' Spectra of GPS Signals in L1.]]

We can clearly recognize that GPS L1C concentrates more power at higher frequencies – due to BOC(6,1) – in the pilot channel than in the data channel (please refer to [[Time-Multiplexed BOC (TMBOC)]] for further details).

Finally, it is important to note that for all the figures next the commonly used expressions for bandwidths in MHz must be understood as multiplied by the factor 1.023. Thus BPSK(10) refers in reality to a BPSK signal with a chip rate of 10.23 MHz. This remains valid for all the bandwidths in this thesis, unless different stated.

== GPS L2 Band ==
GPS is transmitting in the L2 band (1227.60 MHz) a modernized civil signal known as L2C designed specifically to meet commercial needs as it enables the development of dual-frequency solutions; together with the P(Y) Code and the M-Code. The P(Y) Code and M-Code were already described shortly in the previous chapter and the properties and parameters are thus similar to those in the L1 band. In addition, for Block IIR-M, IIF, and subsequent blocks of SVs, two additional PRN ranging codes are transmitted. They are the L2 Civil Moderate (L2 CM) code and the L2 Civil Long (L2 CL) code. These two signals are time multiplexed so that the resulting chipping rate is double as high as that of each individual signal. We further describe them in the next lines more in detail:

* L2 CM Code is transmitted in the IIR-M, IIF, III and subsequent blocks. The PRN L2 CM Code for SV number i is a ranging code, <math>CM_i(t)</math>, which is 20 milliseconds in length at a chipping rate of 511.5 Kbps. The epochs of the L2 CM Code are synchronized with the X1 epochs of the P-code. The <math>CM_i(t)</math> sequence is a linear pattern which is short cycled every count period of 10,230 chips by resetting with a particular initial state. Furthermore, for Block IIR-M, the navigation data is also Modulo-2 added to the L2 CM Code. It is interesting to note that the navigation data can be used in one of two different data rates selectable by ground command:

::* D(t) with a data rate of 50 bps
::* D(t) with a symbol rate of 50 symbols per second (sps) which is obtained by encoding D(t) with a data rate of 25 bps coded in a rate 1/2 convolutional code. Finally, the resultant bit-train is combined with the L2 CL Code using time-division multiplexing.

* L2 CL Code is transmitted in the IIR-M, IIF, III and subsequent blocks. The PRN L2 CL Code for SV number is a ranging code, <math>CL_i(t)</math>, which is 1.5 seconds in length at a chipping rate of 511.5 Kbps. The epochs of the L2 CL Code are synchronized with the X1 epochs of the P Code. The <math>CL_i(t)</math> sequence is a linear pattern which is generated using the same code generator polynomial as of <math>CM_i(t)</math>. However, the <math>CL_i(t)</math> sequence is short cycled by resetting with an initial state every count period of 767,250 chips.

Finally, it is important to note that the GPS L2 band will have a transition period from the C/A Code to L2C and mixed configurations could occur. Next figure shows the baseband L2 signal generation scheme. As we can recognize, although the chipping rate of the L2 CM and L2 CL signals is of 511.5 Kbps individually, after the time multiplexing the composite signal results in a stream of 1.023 MHz.

::::[[File:Chapter_2_Modulation_scheme_GPS_L2_Signals.png |none|thumb|520px|'''''Figure 2:''''' Modulation scheme for the GPS L2 Signals.]]

The technical characteristics of the GPS L2 signals are summarized next:

::::[[File:Chapter_2_Table_2.png |none|thumb|520px|'''''Table 2:''''' GPS L2 signal technical characteristics.]]

The spectra of the different signals described in the preceding lines are shown in the next Figure 3:

::::[[File:Chapter_2_Spectra_GPS_Signals_L2.png|none|thumb|520px|'''''Figure 3:''''' Spectra of the GPS Signals in L2.]]

==GPS L5 Band==
The GPS L5 (1176.45 MHz) signal is one of the new signals belonging to the GPS modernization plan. It is broadcast in a radio band reserved exclusively for aviation safety services and the signal is thought to be used in combination with L1 C/A to improve accuracy (via ionospheric correction) and robustness (via signal redundancy). It is transmitted at a higher power level than current civil GPS signals, has a wider bandwidth and has lower frequency which enhances reception for indoor users.

The L5 signal consists of two carrier components that are in phase quadrature with each other. Each carrier component is bi-phase shift key (BPSK) modulated by a separate bit train. One bit train is module-2 sum of the I5-code, NAV data, and synchronization sequence while the other is the Q5-code with no NAV data, but with another synchronization sequence. For a particular SV, all transmitted signal elements (carriers, codes, synchronization sequence and data) are coherently and derived from the same on-board frequency source.

The L5 data channel and the L5 pilot channel are the two carrier frequencies. Moreover, two PRN ranging codes are transmitted on L5. The PRN L5-codes for SV number i are independent, but time synchronized ranging codes ,<math>X_I^i(t) </math> and <math> X_Q^i(t) </math>, of 1 millisecond in length at a chipping rate of 10.23 Mbps [GPS ICD-705]<ref name="GPS_SIS_ICD_705">[https://archive.gps.gov/technical/icwg/IRN-IS-705J-003.pdf GPS ICD-705 "Navstar GPS Space Segment/User Segment L5 Interfaces"]</ref>. For each code, the 1-millisecond sequences are the modulo-2 sum of two sub-sequences referred to as XA and XBi with lengths of 8,190 chips and 8,191 chips respectively, which restart to generate the 10,230 chip code. The XBi sequence is selectively delayed, thereby allowing the basic code generation technique to produce the different satellite codes.

The generation scheme can be shown graphically as follows:

::::[[File:Chapter_2_Modulation_scheme_GPS_L5_Signals.png |none|thumb|520px|'''''Figure 4:''''' Modulation scheme for the GPS L5 Signals.]]

For more details on L5, refer to [E. D. Kaplan and C. Hegarty, 2006]. The different signals present the following spectrum:

::::[[File:Chapter_2_Spectra_GPS_Signals_L5.png|none|thumb|520px|'''''Figure 5:''''' Spectra of the GPS Signals in L5.]]

To conclude, the technical characteristics of the GPS signals in L5 can be summarized as follows:

::::[[File:Chapter_2_Table_3.png |none|thumb|520px|'''''Table 3:''''' GPS L5 signal technical characteristics.]]

== GPS Modernization ==

Before December 2005 the basic GPS capability consisted of the Standard Positioning Service (SPS) provided by the C/A Code on the L1 frequency and the Precise Positioning Service (PPS) provided by the P(Y) Code on L1 and L2. Although those services are of relatively good quality, the United States proposed a [[GPS_Future_and_Evolutions|modernization plan]] in order to improve the quality and protection of both civil and military users which includes, among other features, the provision of additional signals (e.g. L5, L1C). These signals are being gradually deployed in the GPS system while the constellation is being renewed.

==References==
<references/>

== Credits ==
The information presented in this NAVIPEDIA’s article is an extract of the PhD work performed by Dr. Jose Ángel Ávila Rodríguez in the FAF University of Munich as part of his Doctoral Thesis “On Generalized Signal Waveforms for Satellite Navigation” presented in June 2008, Munich (Germany)

The information of this article is regularly updated in line with the GPS modernization plan updates. Applicable GPS ICD documents can be found in https://archive.gps.gov/technical/icwg/
[[Category:GNSS Signals]]
[[Category:GPS]]
[[Category:GPS Signal Structure]]

GPS and Galileo Satellite Coordinates Computation

2026-04-17T12:51:34Z

Gema.Cueto: Updated reference ICD/SDD links

GPS Architecture

2026-04-17T12:45:18Z

Gema.Cueto: Updated reference ICD/SDD links

{{Article Infobox2
|Category=GPS
|Editors=GMV
|Level=Basic
|YearOfPublication=2011
|Logo=GMV
|Title={{PAGENAME}}
}}
The GPS architecture is divided into three major segments: a [[GPS Space Segment]] (SS), a [[GPS Ground Segment]] (CS), and a [[GPS User Segment]] (US).

==The Space Segment==
The main functions of the [[GPS Space Segment]] are to transmit radio-navigation signals with a specific signal structure, and to store and retransmit the navigation message sent by the Control Segment. These transmissions are controlled by highly stable atomic clocks on board the satellites.

The United States is committed to maintaining the availability of at least 24 operational GPS satellites, 95% of the time. To ensure this commitment, the Air Force has been flying 31 operational GPS satellites for the past few years.<ref name="Space">[https://www.gps.gov/systems/gps/space/ GPS Space Segment information in GPS official website]</ref>

==The Ground Segment==
The [[GPS Ground Segment]] (also referred to as Control Segment) is the responsible for the proper operation of the GPS system.

The Ground Segment is comprised of four major subsystems: <ref name="Ground">[https://www.gps.gov/systems/gps/control/ GPS Ground Segment in GPS official website]</ref>
* Master Control Station (MCS)
* Alternate Master Control Station
* Network of ground antennas (GAs),
* Network of globally-distributed monitor stations (MSs).

The Master Control Station (MCS) processes the measurements received by the Monitor Stations (MS) to estimate satellite orbits (ephemerides) and clock errors, among other parameters, and to generate the navigation message. These corrections and the navigation message are uploaded to the satellites through the Ground Antennas, which are co-located in four of the Monitor stations (Ascension Island, Cape Canaveral, Diego Garcia, and Kwajalein).

==The User Segment==
The [[GPS User Segment]] is composed by [[GPS Receivers]]. Their main function is to receive GPS signals, determine pseudoranges (and other observables), and solve the navigation equations in order to obtain their coordinates and provide a very accurate time. Please refer to [[GNSS Receivers General Introduction|GNSS Receivers]].

==Boundaries Among Segments==
[[File:GPS_architecture.png|GPS segments|right|thumb|300px]]

The communication boundaries between these three segments are documented in the Interface Control Documents (ICDs):<ref>[https://archive.gps.gov/technical/icwg/ GPS Interface Control Documents ICDs]</ref>
# IS-GPS-200:<ref name=" IS-GPS-200-E ">[https://archive.gps.gov/technical/icwg/IS-GPS-200N.pdf Interface Specification IS-GPS-200]</ref> defines the requirements related to the interface between the GPS space and user segments of the GPS for radio frequency (RF) link 1 (L1) and link 2 (L2).
# IS-GPS-705):<ref name=" IS-GPS-705A ">[https://archive.gps.gov/technical/icwg/IS-GPS-705J.pdf Interface Specification IS-GPS-705]</ref> defines the requirements related to the interface between the GPS space and user segments of the GPS for radio frequency (RF) link 5 (L5).
# IS-GPS-800:<ref name"IS-GPS-800">[https://archive.gps.gov/technical/icwg/IS-GPS-800J.pdf Interface Specification IS-GPS-800]</ref> Defines the characteristics of the L1 Civil (L1C) signal transmitted from GPS satellites to navigation receivers on radio frequency link 1 (L1).
# IS-GPS-240::<ref name"IS-GPS-240">[https://archive.gps.gov/technical/icwg/ICD-GPS-240D.pdf Interface Specification IS-GPS-240]</ref> Defines the functional data transfer interface between the GPS Control Segment (CS) and the GPS user and user-support communities during the Operational Control System (OCS) / Architecture Evolution Plan (AEP) system era.
# ICD-GPS-870:<ref name=" ICD-GPS-870 ">[https://archive.gps.gov/technical/icwg/ICD-GPS-870E.pdf Interface Specification ICD-GPS-870]</ref> This ICD defines the functional data transfer interface between the GPS Next Operational Control System (OCX) and the GPS user and user-support communities; captures the same interface as ICD-GPS-240, but for the OCX era.

== Civil GPS Service Interface Committee ==
The Civil GPS Service Interface Committee (CGSIC) is the recognized worldwide forum for effective interaction between all civil GPS users and the U.S. GPS authorities. The U.S. Coast Guard Navigation Center (NAVCEN) coordinates and manages CGSIC in cooperation with the Department of Transportation. The Department of Transportation established CGSIC to exchange information about GPS with the civil user community, respond to the needs of civil GPS users, and integrate GPS into civil sector applications. Information from CGSIC members and meetings is provided to United States GPS authorities for consideration in GPS policy development and GPS service operation.<ref name = "CGIC">[https://www.gps.gov/cgsic/ Civil GPS Service Interface Committee in GPS official website]</ref>

==Notes==
<references group="footnotes"/>
==References==
<references/>

[[Category:GPS|Architecture]]

GPS General Introduction

2026-04-17T12:37:28Z

Gema.Cueto: Updated reference ICD/SDD links

{{Article Infobox2
|Category=GPS
|Editors=GMV
|Level=Basic
|YearOfPublication=2011
|Logo=GMV
|Title={{PAGENAME}}
}}
The [[:Category:GPS|GPS]] is the U.S. Global Navigation Satellite System (GNSS) which provides free positioning and timing services worldwide.
GPS receivers compute their position in the GPS Reference System using satellite technology and based on triangulation principles (please refer to [[An intuitive approach to the GNSS positioning|GNSS positioning]]).
Originally developed for the U.S. military, the incident with the Korean Air Lines Flight 007<ref>[http://en.wikipedia.org/wiki/Korean_Air_Lines_Flight_007 Korean Air Lines Flight 007]</ref> led the US Government to decide to make GPS use free for civilian purposes very early in the experimental phase of GPS .<ref>[http://en.wikipedia.org/wiki/Global_Positioning_System Global Positioning System on Wikipedia]</ref>
The launch of the first Block I Navstar GPS satellite meant the beginning of the deployment of the GPS system on 22 February 1978,<ref>[http://www.astronautix.com/g/gpsblock1.html Block 1 Satellite Information]</ref> followed by the declaration of the Initial Operating Capability in December 1993 with 24 operational satellites in orbit, and the Full Operational Capability in June 1995.
GPS is maintained by the United States government and is freely accessible by anyone with a GPS receiver. The Department of Defense is responsible for operating the system, but it also receives national-level attention and guidance through the National Executive Committee for Space-Based Positioning, Navigation, and Timing (PNT).<ref>[https://www.gps.gov/governance/excom/ Federal Agencies]</ref>

[[File:GPS_satellite_block_IIR_M.png|GPS block IIR-M satellite|thumb|right|300px]]

==GPS Signal Structure==
GPS satellite program started to transmit right-hand circularly polarized signals to the earth at two frequencies, designated L1 and L2.
The main GPS carrier signal L1, at 1575.42MHz, is modulated by two codes: the coarse/acquisition (C/A) code also known as civilian code and the precision/secure (P/Y) code, reserved by cryptographic techniques to military and authorized civilian users.
The GPS L2 signal, centered at 1227.6 MHz, only contains the precise code and it was established to provide a second frequency for ionospheric group delay correction.

The GPS modernization program began in 2005 with the launch of the first IIR-M satellite. Since that moment on, two new signals are transmitted:<ref name="BlockII-Info">[https://space.skyrocket.de/doc_sdat/navstar-2.htm Block II Satellite Information]</ref> L2C for civilian users and a new military signal (M code) in L1 and L2 to provide better jamming resistance than the Y code.<ref>[https://www.mitre.org/sites/default/files/pdf/betz_overview.pdf Capt. B.C.Barker et al., ''Overview of the GPS M Code Signal'']</ref>

Moreover, a new radio frequency link (L5 at 1176.45 MHz) for civilian users has been included in a radio band reserved exclusively for aviation safety services. This signal, available since the launch of the Block IIF<ref name="BlockII-Info"/> satellites (May 28th 2010) has been designed to be compatible with other GNSS systems such as Galileo.

A new signal in L1 frequency band called LC1 has also been included to be interoperable with Galileo E1 signal among others. It is compatible with legacy L1 signal but broadcast at a higher power level and includes advanced design for enhanced performance.

Please refer to [[GPS Signal Plan]] article for further details on GPS Signal structure.

==GPS Reference Frame==
Accurate and well-defined Time References and Coordinate Frames are essential in GNSS, where positions are computed from signal travel time measurements and provided as a set of coordinates.
GPS uses the World Geodetic System WGS-84,<ref name="GNSS-Book ">J. Sanz Subirana, JM. Juan Zornoza and M. Hernández-Pajares, ''Global Navigation Satellite Systems: Volume I: Fundamentals and Algorithms''</ref> developed by the US Defence Department, which is a unified terrestrial reference system for position and vector referencing. Indeed, the GPS broadcast ephemeris are linked to the position of the satellite antenna phase centre in the WGS-84 reference frame. Thus, the user receiver coordinates will be expressed in the same ECEF frame.
GPS System Time (GPST) is defined by the [[GPS Ground Segment| GPS Ground Segment]] on the basis of a set of atomic clocks aboard the satellites and in the Monitor Stations. It is not adjusted for leap seconds and it is synchronized with the UTC (USNO) at nanosecond level.
The origin epoch of GPS time is 0h UTC (midnight) of January 5th to 6th of 1980.

==GPS Services==
GPS provides two different positioning [[GPS Services|services]], namely the Precise Positioning Service (PPS) and the Standard Positioning Service (SPS):
# The Standard Positioning Service (SPS),<ref name="SPS-Standard ">[https://archive.gps.gov/technical/ps/2020-SPS-performance-standard.pdf Global Positioning System Standard Positioning Service Performance Standard]</ref> is a positioning and timing service provided on GPS L1, L2 and L5 frequencies and available to all GPS users. The L1 frequency contains a coarse acquisition (C/A) code and a navigation data message. The L2 frequency contains a CM-code and CL-code signals whereas I5-code and Q5-code signals are transmitted in L5 frequency.
# The Precise Positioning Service (PPS.<ref name="PPS-Standard">[https://archive.gps.gov/technical/ps/2007-PPS-performance-standard.pdf Global Positioning System Precise Positioning Service Performance Standard]</ref> is a highly accurate military positioning, velocity and timing service broadcasted at the GPS L1 and L2 frequencies. Both frequencies contain a precision (P) code ranging signal with a navigation data message that is reserved for authorized use by the use of cryptography.

==GPS Architecture==
[[GPS Architecture|GPS architecture]] is comprised of three segments: a [[GPS Space Segment|GPS Space Segment]], a [[GPS Ground Segment|GPS Ground Segment]], and a [[GPS User Segment|GPS User Segment]].
The main functions of the [[GPS Space Segment|GPS Space Segment]] are to transmit radio-navigation signals, and to store and retransmit the navigation message sent by the [[GPS Ground Segment|GPS Ground Segment]].
The [[GPS Ground Segment|GPS Ground Segment]] is composed of a master control station, a network of monitor stations and ground antennas which upload the clock and orbit errors, as well as the navigation data message to the GPS satellites.<ref name="GNSS-Book "/>
Finally, the [[GPS User Segment|GPS User Segment]] consists on the millions of receivers performing the navigation, timing or other related functions.

==Differential GPS==
[[Differential GPS| Differential GPS]] is an enhancement to primary GPS constellation(s) information by the use of a network of ground-based reference stations which enable the broadcasting of differential information to the user – also named rover – to improve the accuracy of his position – the integrity is not assured. There are several differential GNSS techniques, such as the classical DGPSs (or [[Differential GPS|DGPS]]), the [[Real Time Kinematics]] (RTK) and the [[Wide Area RTK (WARTK)]].

==GPS Performances==
The levels of [[GPS Performances|performance]] that the user can expect from GPS are specified in the Standard Positioning Service Performance Standard,<ref name="SPS-Standard "/> and the Precise Positioning Standard.<ref name="PPS-Standard"/> However, the values provided by these documents are very conservative, being the actual performances usually better than these official values.
Moreover, the performance obtained with GPS depends strongly on the mode of operation. For instance, a stand-alone receiver that uses only the signals received from the satellites, the levels of performance are:<ref>The Modernization of GPS: Plans, New Capabilities and the Future Relationship to Galileo, Keith D. McDonald </ref>
* C/A-code receivers ~ 5 -10 m.
* P/Y-code receivers ~ 2 -9 m
In case of using GPS in a differential mode, the performances that can be expected are:
* C/A-code DGPS receivers ~0.7 -3 m.
* P/Y-code DGPS receivers ~0.5 -2.0 m.

==GPS Future and Evolutions==
Aimed at improving the performance for civilian users, the [[GPS Future and Evolutions|GPS modernization]] will introduce the following signals:<ref>[http://www.gps.gov/systems/gps/modernization/2006-fact-sheet.pdf GPS Modernization Fact Sheet]</ref><ref>[https://www.gps.gov/systems/gps/modernization/ GPS Official website]</ref>
* L2C (1227.6 MHz: It enables the development of dual-frequency civil GPS receivers to correct the ionospheric group delay. This signal is available since 2005, with the launch of the first IIR-M satellite.<ref>[https://web.stanford.edu/group/scpnt/pnt/PNT10/presentation_slides/2-PNT_Symposium_Gruber.pdf GPS Modernization and Program Update, Bernie Gruber]</ref>
* L5C (1176.45 MHz): It is compatible with other GNSS systems and is transmitted at a higher power than current civil GPS signals, also with a wider bandwidth. This signal is available since the launch of the Block IIF satellites (May 28th 2010).
* L1C (1575.42 MHz): Designed for interoperability with Galileo, it is backward compatible with the current civil signal on L1. This signal is available since the launch of the Block IIIA satellites (first satellite launched December 2018). An enhancement to this L1C signal is being analysed, which is called CHIMERA (Chips Message Robust Authentication). This technique consists on adding encrypted watermarks to the L1C signal that not only let users know when a signal is being spoofed but also makes it possible to [[GNSS Authentication and encryption | authenticate]] the location of a GPS receiver to another party.

In addition to the civil signals, it is planned to include a new military signal, the M-code, in L1 and L2 frequencies.<ref>[http://www.navcen.uscg.gov/pdf/ModernizedL2CivilSignal.pdf The Modernized L2 Civil Signal, by Richard D. Fontana, Wai Cheung, and Tom Stansell, GPS World September 2001]</ref>
Regarding the Ground Segment, the new Operational Control Segment (OCX) will replace the current GPS Operational Control System placed at Schriever Air Force Base.<ref name=NEW_OCX>[http://www.gps.gov/governance/advisory/meetings/2010-10/canty.pdf GPS OCX Update]</ref> The OCX will maintain backwards compatibility with the Block IIR and IIR-M constellation satellites, providing command and control of the new GPS IIF and GPS III families of satellites, and enabling new modernized civil signal capabilities.<ref name=NEW_OCX/>

[[File:GPS_modernization.png|GPS Modernization|center|frame]]

==Credits==
This article contains some verbatim paragraphs taken from U.S. governmental web pages. Please see the References section.

==Notes==
<references group="footnotes"/>
==References==
<references/>

[[Category:GPS|!]]

GPS User Segment

2026-04-17T12:29:43Z

Gema.Cueto: Updated reference ICD/SDD links

{{Article Infobox2
|Category=GPS
|Editors=GMV
|Level=Basic
|YearOfPublication=2011
|Logo=GMV
|Title={{PAGENAME}}
}}
The GPS User Segment consists on L-band radio receiver/processors and antennas which receive GPS signals, determine pseudoranges (and other observables), and [[An intuitive approach to the GNSS positioning|solve the navigation equations]] in order to obtain their coordinates and provide a very accurate time.

[[GNSS Market Report#Report Overview|The GNSS Market Report, Issue 3]], provided by European GNSS Agency, estimated that the number of GNSS enabled devices in 2012 were about two billion units, from which the 100% were GPS capable. The GNSS installed based in 2019 has increased to 6.4 billion units, in which all of them are at least GPS enabled<ref name="Market Report 2020">[https://www.gsa.europa.eu/system/files/reports/market_report_issue_6_v2.pdf GSA GNSS Market Report 2019, Issue 6]</ref><ref name= "User Report 2020">[https://www.gsa.europa.eu/sites/default/files/uploads/technology_report_2020.pdf GSA User technology report, Issue 3]</ref>.

==GPS Receivers==
A [[GPS Receivers|GPS Receiver]] is a device capable of processing the signal of the GPS satellites and determining the user position, velocity and precise time (PVT) by processing the signal broadcasted by satellites.

Any navigation solution provided by a [[GNSS Receivers General Introduction|GNSS Receiver]] is based on the computation of its distance to a set of satellites, by means of extracting the propagation time of the incoming signals traveling through space at the speed of light, according to the satellite and receiver local clocks.

Notice that satellites are always in motion, so previous to obtaining the navigation message, the satellite’s signal is detected and tracked. The receiver’s functional blocks that perform these tasks are the antenna, the front-end and the baseband signal processing (in charge of acquiring and tracking the signal).

Once the signal is acquired and tracked, the receiver application decodes the navigation message and estimates the user position. The Navigation Message includes:<ref name="GNSS-Book ">J. Sanz Subirana, JM. Juan Zornoza and M. Hernández-Pajares, ''Global Navigation Satellite Systems: Volume I: Fundamentals and Algorithms''</ref>
* Ephemeris parameters, needed to compute the satellite’s coordinates
* Time parameters and Clock Corrections, to compute satellite clock offsets and time conversions
* Service Parameters with satellite health information
* Ionospheric parameters model needed for single frequency receivers
* Almanacs, needed for the acquisition of the signal by the receiver. It allows computing the position of all satellites but with a lower accuracy than the ephemeris

The ephemeris and clocks parameters are usually updated every two hours, while the almanac is updated at least every six days.

The GPS Signal In Space is specified in the following documents:<ref>[https://archive.gps.gov/technical/icwg/ GPS Interface Control Documents]</ref>
* IS-GPS-200: Interface between the space segment of the Global Positioning System and the navigation user segment of the GPS for radio frequency link 1 (L1) and link 2 (L2)
* IS-GPS-705: interface between the space segment of the Global Positioning System and the navigation user segment of the GPS for radio frequency link 5 (L5).
* IS-GPS-800: interface between the space segment of the Global Positioning System and the navigation user segment of the GPS for signal L1 Civil (L1C) transmitted in the frequency band of L1.

Receivers can be categorized by their type in different ways, and under different criteria. For instance, receivers can be stand-alone, or may benefit from corrections or measurements provided by augmentation system or by receivers in the vicinities (DGPS).
Moreover receivers might be generic all-purpose receivers or can be built specifically having the application in mind:<ref name="GPS_APP">[http://en.wikipedia.org/wiki/GNSS_applications GNSS applications on Wikipedia]</ref> navigation, accurate positioning or timing, surveying, etc.
In addition to position and velocity, GPS receivers also provide time. An important amount of economic activities, such wireless telephone, electrical power grids or financial networks rely on precision timing for synchronization and operational efficiency.<ref>[http://www.gps.gov/applications/timing/ Timing on gps.gov]</ref> GPS enables the users to determine the time with a high precision without needing to use expensive atomic clocks.

==Applications==
[[GNSS Applications|GPS applications]] are all those applications that use GPS to collect position, velocity and time information to be used by the application.
As stated by the US Government, the position and velocity provided by GPS may be used for [[Civil Applications|civil applications]] such as:<ref>[http://www.gps.gov/applications GPS applications on gps.gov]</ref>
* '''Agriculture''': GPS-based applications in precision farming are being used for farm planning, field mapping, soil sampling, tractor guidance, crop scouting, variable rate applications, and yield mapping.
* '''Aviation''': GPS provides position determination for all phases of flight from departure, en route, and arrival, to airport surface navigation.
*'''Environment''': GPS provides accurate and timely information to support better decision making related to the Earth's environment
*'''Marine''': GPS provides the fastest and most accurate method for mariners to navigate, measure speed, and determine location. This enables increased levels of safety and efficiency for mariners worldwide.
*'''Public Safety and Disaster Relief''': A critical component of any successful rescue operation is time. Knowing the precise location of landmarks, streets, buildings, emergency service resources, and disaster relief sites reduces that time -- and saves lives. This information is critical to disaster relief teams and public safety personnel in order to protect life and reduce property loss. The Global Positioning System (GPS) serves as a facilitating technology in addressing these needs.
*'''Rail''': Rail system use the GPS in combination with other sensors to maintain smooth flow of traffic, prevent collisions by precise knowledge of where a train is located, increase efficiency and capacity, etc.
*'''Recreation''': GPS has eliminated many of the hazards associated with common recreational activities by providing a capability to determine a precise location. GPS receivers have also broadened the scope and enjoyment of outdoor activities by simplifying many of the traditional problems, such as staying on the “correct trail” or returning to the best fishing spot.
*'''Roads and Highways''': GPS may be used to provide in-vehicle navigation, fleet management, tolling applications, etc.* '''Surveying and mapping''': The main limitation of the traditional surveying techniques is the requirement for a line of sight between surveying points. Using the accurate position provided by GPS surveying and mapping results can be obtained faster and with a lower cost.
*'''Space''': GPS is revolutionizing and revitalizing the way nations operate in space, from guidance systems for crewed vehicles to the management, tracking, and control of communication satellite constellations, to monitoring the Earth from space.
*'''Surveying and mapping''': The main limitation of the traditional surveying techniques is the requirement for a line of sight between surveying points. Using the accurate position provided by GPS surveying and mapping results can be obtained faster and with a lower cost.
*'''Timing''': GPS enables users to determine the time to within 100 billionths of a second, without the cost of owning and operating atomic clocks. Precise time is crucial to a variety of economic activities around the world. Communication systems, electrical power grids, and financial networks all rely on precision timing for synchronization and operational efficiency.

<gallery>
Image:app_transport.png
Image:app_agriculture.png
Image:app_survey.jpg
</gallery>

==Notes==
<references group="footnotes"/>
==References==
<references/>

[[Category:GPS]]
[[Category:GPS User Segment]]

GPS Services

2026-04-17T12:26:25Z

Gema.Cueto: Updated reference ICD/SDD links

{{Article Infobox2
|Category=GPS
|Editors=GMV
|Level=Basic
|YearOfPublication=2011
|Logo=GMV
|Title={{PAGENAME}}
}}
GPS provides two different positioning services: the Precise Positioning Service (PPS) and the Standard Positioning Service (SPS).

==Precise Positioning Service==
As defined by the United States Government the GPS<ref>[https://archive.gps.gov/technical/ps/2007-PPS-performance-standard.pdf Global Positioning System Precise Positioning Service Performance Standard]</ref> Precise Positioning Service (PPS) is ''a positioning and timing service provided by way of authorized access to ranging signals broadcast at the GPS L1 and L2 frequencies. The L1 frequency, transmitted by all Navstar satellites, contains a coarse/acquisition (C/A) code ranging signal, with a navigation data message, that is available for peaceful civil, commercial, and scientific use; and a precision (P) code ranging signal with a navigation data message, that is reserved for authorized use. The P-code will normally be cryptographically altered to become the Y-code. The Y-code will not be available to users that do not have valid cryptographic keys. Navstar satellites also transmit a second P- or Y-(P(Y)-) code ranging signal with a navigation data message at the L2 frequency''.

In order to restrict civilian user access to full system accuracy, the following protections were introduced:
* '''S/A or Selective Availability''': intentional satellite clock degradation (process-δ) and ephemeris manipulation (process-ε). The effect on horizontal positioning implies going from about 10m (S/A=off) to 100m (S/A=on).<ref name="GNSS-Book ">J. Sanz Subirana, JM. Juan Zornoza and M. Hernández-Pajares, ''Global Navigation Satellite Systems:
Volume I: Fundamentals and Algorithms''</ref> The process-δ acts directly over satellite clock fundamental frequency, which has a direct impact on pseudoranges to be calculated by user's receivers. The process-ε consists in truncating information related to the orbits.
[[File:SA_removal.png|GPS accuracy before and after SA removal|thumb|right]]
USA President Bill Clinton ordered the termination of GPS Selective Availability on May 1st, 2000.<ref>[http://www.navcen.uscg.gov/?pageName=gpsSelectiveAvailability Announcement of the cessation of GPS Selective Availability on May 1st, 2000]</ref> In September 2007, this decision was confirmed by the fact that the U.S. Government decided to procure the next generation of GPS satellites, GPS III, without the SA feature. This decision eliminates an important source of uncertainty that generated considerable concern among civil users.<ref>[http://georgewbush-whitehouse.archives.gov/news/releases/2007/09/20070918-2.html GPS III, without the SA feature]</ref>

* '''A/S or Anti-Spooffing''': it consists in P code encryption by combining it with a secret W code, resulting in the Y code, which is modulated over the two carriers L1 and L2. This serves the twofold purpose of protecting the code so that it can only be used by authorised receivers and avoiding adversaries to forge a misleading signal that could confuse military receivers. The use of A/S does not prevent civil users to take benefit from the C/A code.

Authorised users receive the corresponding encryption keys to access the PPS free from SA and A-S, and hence obtain the maximum accuracy from GPS. Should a PPS receiver have not been fed with valid keys, it could still behave as a SPS receiver.

The P(Y)-code, which is reserved for military use and authorised civilian users, is modulated over both carriers L1 and L2, and defines the Precise Positioning Service (PPS): it is reserved for military use and authorized civilian users. With a chipping-rate of 10Mbps and a wavelength of 29.31 m, the P(Y)-code is repeated every 38 weeks; a weekly portion, known as PRN, is assigned to each satellite.

Please refer to [[GPS Performances|GPS Performances]] for more information about the performances provided by the PPS service.

==Standard Positioning Service==
As defined by the United States Government is<ref>[https://archive.gps.gov/technical/ps/2020-SPS-performance-standard.pdf Global Positioning System Standard Positioning Service Performance Standard, 5th Ed. April 2020]</ref> the GPS Standard Positioning Service (PPS) is ''a positioning and timing service that it is available for peaceful civil, commercial and scientific use. It includes the C/A-code signal, the CM/CL-code signals, and the I5-code/Q5- code signals. The C/A-code signal is transmitted by all satellites and comprises an L1 carrier modulated by a coarse/acquisition (C/A) code ranging signal with a legacy navigation (LNAV) data message. The CM-code and CL-code signals are transmitted by some satellites and comprise an L2 carrier modulated by both a civil moderate length (CM) code ranging signal with a civil navigation (CNAV) data message and a civil long length (CL) code ranging signal without a data message. The I5-code and Q5-code signals are transmitted by some satellites and comprise an L5 carrier modulated by both a civil in-phase (I5) code ranging signal with a CNAV data message and a civil quadrature-phase (Q5) code ranging signal without a data message.

The Standard Positioning Service is therefore based on:
*The Coarse/Acquisition code (C/A(t)), which is modulated only on L1. It has a chipping-rate of 1.023 MHz, and contains 1 023 chips, so that the code is repeated every millisecond and each chip lasts about 1 µs, meaning a chip-width or wavelength of 293.1 metre.
*CM/CL-code signals are both modulated in L2:
**Civil Medium (CM) code is 20 milliseconds in length at a chipping rate of 511,5 kpbs.
**Civil Long (CL) code is 1.5 seconds in length at a chipping rate of 511,5 kpbs.
*In-phase (I5) and Quadraphase (Q5) signals are modulated in L5. They are independent but time synchronized, 1 millisecond in length with a chipping rate of 10.23 Mbps.

Please refer to [[GPS Performances]] for more information about the performances provided by the SPS service.

==Notes==
<references group="footnotes"/>
==References==
<references/>

[[Category:GPS]]
[[Category:GPS Services]]

GPS Receivers

2026-04-17T12:22:35Z

Gema.Cueto: Updated reference ICD/SDD links

{{Article Infobox2
|Category=GPS
|Editors=GMV
|Level=Basic
|YearOfPublication=2011
|Logo=GMV
|Title={{PAGENAME}}
}}
A GPS Receiver is a L-band radio processor capable of [[An intuitive approach to the GNSS positioning|solving the navigation equations]] in order to determine the user position, velocity and precise time (PVT), by processing the signal broadcasted by GPS satellites.

[[GNSS Market Report#Report Overview|The GNSS Market Report, Issue 3]], provided by European GNSS Agency, has estimated that the number of GPS enabled devices in 2012 were about two billion units.

==GPS Receivers==

Any navigation solution provided by a [[GNSS Receivers General Introduction|GNSS Receiver]] is based on the computation of its distance to a set of satellites, by means of extracting the propagation time of the incoming signals traveling through space at the speed of light, according to the satellite and receiver local clocks.

Notice that satellites are always in motion, so previous to obtaining the navigation message, the satellite’s signal is detected and tracked. The [[Generic Receiver Description|receiver’s functional blocks]] that perform these tasks are the antenna, the front-end and the baseband signal processing (in charge of acquiring and tracking the signal).

Once the signal is acquired and tracked, the receiver application decodes the navigation message and estimates the user position. The Navigation Message includes:<ref name="GNSS-Book ">J. Sanz Subirana, JM. Juan Zornoza and M. Hernández-Pajares, ''Global Navigation Satellite Systems: Volume I: Fundamentals and Algorithms''</ref>
* Ephemeris parameters, needed to compute the satellite’s coordinates.
* Time parameters and Clock Corrections, to compute satellite clock offsets and time conversions.
* Service Parameters with satellite health information.
* Ionospheric parameters model needed for single frequency receivers.
* Almanacs, that allow computing the position of all satellites but with a lower accuracy than the ephemeris.

The ephemeris and clocks parameters are usually updated every two hours, while the almanac is updated at least every six days.

The GPS Signal In Space is specified in the following documents:<ref>[https://archive.gps.gov/technical/icwg/ GPS Interface Control Documents]</ref>
* IS-GPS-200E: Interface between the space segment of the Global Positioning System and the navigation user segment of the GPS for radio frequency link 1 (L1) and link 2 (L2)
* IS-GPS-705A: interface between the space segment of the Global Positioning System and the navigation user segment of the GPS for radio frequency link 5 (L5).
* IS-GPS-800: interface between the space segment of the Global Positioning System and the navigation user segment of the GPS for signal L1 Civil (L1C) transmitted in the frequency band of L1.

==Particularities==
Each GNSS system uses a specific [[Reference Frames in GNSS|Reference Frame]]; although a multi-constellation receiver is able to convert all information to the same common frame, a GPS-only receiver uses the WGS-84 reference frame.
In an analogous way, each system has its own [[Time References in GNSS|time reference]] defined by the respective control segments; the time reference for GPS is called “GPS Time” (GPST).

Each GNSS System transmits its own navigation message, defined in the respective Signal In Space Interface Control Documents, SIS ICD. As an example, GNSS satellites transmit information that allows the receiver to compute their positions. For the case of GPS (in-line with Galileo but unlike GLONASS), the satellites transmit the orbit parameters as updated by the Ground Segment and refreshed every 2 hours. The GPS receiver then [[GPS and Galileo Satellite Coordinates Computation|computes the satellite position]] based on these transmitted ephemeris parameters.
Another distinction regarding the transmitted navigation message with impact on the receiver is the ionospheric parameters transmitted to support the single frequency receiver in computing the ionospheric error; GPS uses the [[Klobuchar Ionospheric Model]].

GNSS signals modulation, structure, navigation message contents and formats are often different among signals from the same system and from different systems. Most of these characteristics are easily implemented at the receiver (i.e. requiring only “software modifications”, such as the use of different PRN codes or the ability to cope with different message structures). The main difference among GNSS receivers falls into the specific characteristics that have impact at RF level, such as the [[CDMA FDMA Techniques|Multiple Access Techniques]] employed. GPS (as Galileo and BeiDou) uses a CDMA technique allowing a simpler RF module (than for example GLONASS), since all signals in the same frequency band have a common carrier.

It should be noted that the current trend consists on facilitating the access of each system to the receivers, i.e. fomenting multi-constellation receivers. Hence, most discussions and agreements among the systems’ responsibles are conducted in the sense of taking this effort out of the user segment, focusing on [[Principles of Compatibility among GNSS|compatibility]] and [[Principles of Interoperability among GNSS|interoperability]] aspects in the system design.

==Types of GPS Receivers==

Receivers can be categorized by [[Receiver Types|their type]] in different ways, and under different criteria. For instance, receivers can be stand-alone, or may benefit from corrections or measurements provided by augmentation system or by receivers in the vicinities ([[Differential GNSS|DGPS]]).
Moreover receivers might be generic all purpose receivers or can be built specifically having the [[GNSS Applications|application]] in mind: navigation, accurate positioning or timing, surveying, etc.
In addition to position and velocity, GPS receivers also provide time. An important amount of economic activities, such wireless telephone, electrical power grids or financial networks rely on precision timing for synchronization and operational efficiency. GPS enables the users to determine the time with a high precision without needing to use expensive atomic clocks.

The initial purpose of the GPS system was military but with the free availability of GPS signals and the availability of cheap GNSS receivers, the GPS technology is having a pervasive use in civil, industrial, scientific areas. Currently the use of GPS in Civil Applications is generalized, and it is well known that GPS Receivers have been spread very fast as well as the manufacturers dedicated to this (e.g. [http://www.csr.com CSR], [http://www.broadcom.com BroadCom], [http://www.garmin.com Garmin],...).

==Related articles==
*[[GNSS Receivers General Introduction]]
*[[Generic Receiver Description]]
*[[System Design Details]]
*[[Receiver Characteristics]]
*[[Interfaces and Protocols|Interfaces and Protocols]]

==Notes==
<references group="footnotes"/>
==References==
<references/>

[[Category:Receivers]]
[[Category:GPS Receivers]]

GPS Performances

2026-04-17T12:19:21Z

Gema.Cueto: Updated reference ICD/SDD links

{{Article Infobox2
|Category=GPS
|Editors=GMV
|Level=Basic
|YearOfPublication=2011
|Logo=GMV
|Title={{PAGENAME}}
}}
The US Global Positioning System (GPS) provides 24/7 positioning and timing services for worldwide users.

GPS supplies two different service levels, Standard Positioning Service and the Precise Positioning Service:
# The Standard Positioning Service (SPS),<ref name="SPS-Standard ">[https://archive.gps.gov/technical/ps/2020-SPS-performance-standard.pdf Global Positioning System Standard Positioning Service Performance Standard]</ref> is a positioning and timing service provided on GPS L1, L2 and L5 frequencies and available to all GPS users. The L1 frequency contains a coarse acquisition (C/A) code and a navigation data message. The L2 frequency contains a CM-code and CL-code signals whereas I5-code and Q5-code signals are transmitted in L5 frequency.
# The Precise Positioning Service (PPS),<ref name="PPS-Standard "/> is a highly accurate military positioning, velocity and timing service broadcasted at the GPS L1 and L2 frequencies. Both frequencies contain a precision (P/Y) code ranging signal with an encrypted navigation data message that is reserved for authorized users.

==Introduction==

The levels of performance that the user can expect from GPS are specified in the Standard Positioning Service Performance Standard,<ref name="SPS-Standard "/> and the Precise Positioning Service Standard.<ref name="PPS-Standard">[https://archive.gps.gov/technical/ps/2007-PPS-performance-standard.pdf Global Positioning System Precise Positioning Service Performance Standard]</ref> However, the values provided by these documents are very conservative, being the actual performances usually better than these official values.

Moreover, the performance obtained with GPS depends strongly on the mode of operation. For instance, a stand-alone receiver that uses only the signals received from the satellites, the levels of performance are:<ref>The Modernization of GPS: Plans, New Capabilities and the Future Relationship to Galileo, Keith D. McDonald </ref>
* C/A-code receivers ~ 5 -10 m.
* P/Y-code receivers ~ 2 -9 m
In case of using GPS in a differential mode, [[Differential GPS|DGPS]], the performances that can be expected are:
* C/A-code DGPS receivers ~0.7 -3 m.
* P/Y-code DGPS receivers ~0.5 -2.0 m.
More advanced techniques, such as [[Real Time Kinematics|Real Time Kinematics]] or [[Precise Point Positioning]], might provide performances in the order of a few centimeters.

== GPS Service Level Performances==

The Performances of each Service are different and they are specified in the Standard Positioning Service Performance Standard, and the Precise Positioning Standard.

===Standard Positioning Service (SPS) Performances===

The Performance standards for SPS Service based on Single Frequency C/A-Code are:<ref name="SPS-Standard "/>

{| class="wikitable" align="center"
|+align="bottom" |''Service Performances Standards for Standard Positioning Service(SPS)''
|-
! colspan="2"| GPS Performance Standard Metric
! SPS User Performance
! SPS Signal in Space Performance
|- align="center"
! rowspan="2"| Global Accuracy
| All-in-View Horizontal 95%
| <100 m
|< 8 m
|- align="center"
| All-in-View Vertical 95%
| <156 m
| < 13 m
|- align="center"
! rowspan="2"| Worst Site Accuracy
| All-in-View Horizontal 95%
| <100 m
|< 15 m
|- align="center"
| All-in-View Vertical 95%
| <156 m
| < 33 m
|- align="center"
! colspan="2"| User Range Error (URE)
| N/A
| <7.0 m 95% of time
|- align="center"
! colspan="2"| Velocity Accuracy
| N/A
| < 0.2 m/sec 95% velocity error
|- align="center"

! colspan="2"| Time Transfer Accuracy
| N/A
| <30 ns 95% of time
|- align="center"
! colspan="2" rowspan="2"| Geometry (PDOP ≤ 6)
| > 95.86% global
| > 98% global
|- align="center"
| > 83.9% worst site
| > 88% worst site
|- align="center"
! colspan="2"| Constellation Availability
| N/A
| >98% Probability of 21 Healthy Satellites
|}

===Precise Positioning Service (PPS) Performances===

The Performance standards for PPS Service based on Dual Frequency P/Y-Code are:<ref name="PPS-Standard "/>

{| class="wikitable" align="center"
|+align="bottom" |''Service Performances Standards for Precise Positioning Service (PPS)''
|-
! colspan="2"| GPS Performance Standard Metric
! SPS User Performance
! SPS Signal in Space Performance
|- align="center"
! rowspan="2"| Global Accuracy
| All-in-View Horizontal 95%
| < 36 m
|< 13 m
|- align="center"
| All-in-View Vertical 95%
| < 77 m
| < 22 m
|- align="center"
! colspan="2"| User Range Error (URE)
| N/A
| <5.9 m 95% of time
|- align="center"
! colspan="2"| Time Transfer Accuracy
| N/A
| <40 ns 95% of time
|- align="center"
! colspan="2"| Integrity
| N/A
| < 1x10-5 Probability Over Any Hour
|- align="center"
! colspan="2"| Geometry (PDOP ≤ 6)
| >95.7% global
| >98% global
|- align="center"
! colspan="2"| Constellation Availability
| N/A
| >98% Probability of 21 Healthy Satellites
|}

In general, PPS performance standards are in line with SPS ones. Some advantages of PPS Service opposite to the SPS Service are that PPS access to WAGE (Wide Area GPS Enhancements) rapid ephemeris updates and corrections, and the use of dual frequency to correct the delay suffered by the signal in its transmission through the [[Ionospheric Delay|ionosphere]] in real time, which implies a significant performance improvement. The P/Y code is encrypted to avoid spoofing and the access to the service to unauthorised users.

==Modernized Signals Performances==
Since the beginning of the transmission of the CNAV navigation message, by April 2014, the L2C signal is suffering several improvements. On March 2015 the U.S. Air Force reported that signal performance of CNAV matches or slightly outperforms Legacy performance: average user range error (RMS URE) from 25 February – 3 March 2015 was 0.50 m for Legacy and 0.57 m for Modernized; best week for Modernized signals since the broadcast initiated April 2014 was 0.42 m for 6 – 13 January 2015<ref>[http://gpsworld.com/cnav-performance-matches-or-slightly-outperforms-legacy-signals/ CNAV Performance ‘Matches or Slightly Outperforms’ Legacy Signals], GPS World, March 19, 2015</ref>.

==Combined Services Performances==

GPS can be interoperable with other GNSS systems. When combining GPS with other GNSS constellations this enhances positioning performance. This is due to an improvement in [[Availability|availability]], i.e. the number of satellites in view is larger, and geometry.

There are other ways to enhance the GPS positioning solution, such as [[GNSS Augmentation]] systems, or [[Differential GNSS|Differential GNSS]] techniques, that are explained in more detail in the corresponding articles. With DGNSS the [[Accuracy|accuracy]] is improved to the order of 1 m, and the GNSS Augmentation systems assure [[Integrity|integrity]].

==References==
<references/>

[[Category:GPS]]
[[Category:GPS Performance]]

GPS Ground Segment

2026-04-17T12:12:45Z

Gema.Cueto: Updated reference ICD/SDD links

{{Article Infobox2
|Category=GPS
|Editors=GMV
|Level=Basic
|YearOfPublication=2011
|Logo=GMV
|Title={{PAGENAME}}
}}
The GPS Ground Segment (also referred to as Control Segment or Operational Control System) is the responsible for the proper operation of the GPS system.

The GPS Control Segment consists of a global network of ground facilities that track the GPS satellites, monitor their transmissions, perform analysis, and send commands and data to the constellation<ref name=GPS_GS>[https://www.gps.gov/systems/gps/control/ GPS Ground Segment information in GPS official website]</ref>.

==Introduction==
[[File:GPS ground segment.png|GPS Operational Control System|250px|thumb|right]]
[[File:GPSGroundSegment.png | GPS Control Segment<ref name=GPS_GS></ref>|250px|thumb|right]]

The Ground Segment, also referred to as Control Segment or Operational Control System, OCS, is the responsible for the proper operation of the GPS system. The main tasks performed by the CS are the following:
*Monitoring and control of satellite orbital parameters;
*Monitoring health and status of the satellite subsystems (solar arrays, battery power and the level of propellant used for maneuvers);
*Activation of spare satellites;
*Update of parameters in the navigation message (ephemeris, almanac and clock corrections);
*Resolving satellite anomalies;
*Controlling Selective Availability (SA) and Anti-Spoofing (A/S)
*Passive tracking of the satellites.

The Ground Segment is comprised of four major subsystems:<ref name="GPS SPS PS">[https://www.gps.gov/sites/default/files/2025-07/2020-SPS-performance-standard.pdf GPS Standard Positioning Service (SPS) Performance Standard, 5th Edition, April 2020]</ref>
*Master Control Station (MCS)
*Alternate Master Control Station
*Network of ground antennas (GAs),
*Network of globally-distributed monitor stations (MSs).

The current Operational Control Segment (OCS) includes a Master Control Station (MCS), an alternate Master Control Station, 11 command and control antennas (GA), and 16 monitoring sites (MS). The locations of these facilities are shown in the map below.<ref name=GPS_GS></ref>

The Master Control Station (MCS) processes the measurements received by the Monitor Stations (MS) to estimate satellite orbits (ephemerides) and clock errors, among other parameters, and to generate the navigation message. These corrections and the navigation message are uploaded to the satellites through the Ground Antennas, some of them co-located in four of the Monitor stations (Ascension Island, Cape Canaveral, Diego Garcia, and Kwajalein).

==The Master Control Station==
Located at Colorado Springs, the Master Control Station (MCS) is the central control node for the GPS satellite constellation. It is backed up by a fully operational alternate master control station. The MCS is responsible for all aspects of constellation command and control, including:<ref name="GPS SPS PS"/>
*Provides command and control of the GPS constellation.
*Uses global monitor station data to compute the precise locations of the satellites.
*Generates navigation messages for upload to the satellites.
*Monitors satellite broadcast and system integrity to ensure constellation health and accuracy.
*Routine satellite bus and payload status monitoring.
*Performs satellite maintenance and anomaly resolution, including repositioning satellites to maintain optimal constellation.
*Currently uses separate systems (AEP and LADO) to control operational and non-operational satellites.
*Monitoring and management of GPS Signal-In-Space (SIS) performance to comply with all performance standards (SPS PS and PPS PS).
*Navigation message data upload operations as required to sustain performance in accordance with accuracy and integrity performance standards.
*Detecting and responding to GPS SIS failures.

==The Monitor Stations==
They are distributed around the world and equipped with atomic clocks standards and GPS receivers to continuously collect GPS data for all the satellites in view from their locations. The collected data is sent to the Master Control Station where it is processed to estimate satellite orbits (ephemerides) and clock errors, among other parameters, and to generate the Navigation Message. They also collect navigation signals, range/carrier measurements and atmospheric data.

Prior to the modernization program, the Monitor Stations network comprised five sites located in<ref name="GNSS-Book "/>:
*Hawaii,
*Colorado Springs (Colorado, US),
*Ascension Island (South Atlantic),
*Diego Garcia (Indian Ocean),
*Kwajalein (North Pacific).

In order to increase performance and accuracy, new stations were incorporated into the ground segment providing greater visibility of the constellation: Cape Canaveral (Florida, US) was incorporated in 2001 and six new stations in 2005:<ref>[http://www.gps.gov/systems/gps/modernization/2006-fact-sheet.pdf GPS Modernization Fact Sheet]</ref>
*Adelaide (Australia),
*Buenos Aires (Argentina),
*Hermitage (UK),
*Manama (Bahrain),
*Quito (Ecuador)
*Washington DC (USA).

Five more stations were added afterwards in 2006:
*Fairbanks (Alaska),
*Osan (South Korea),
*Papeete (Tahiti),
*Pretoria (South Africa)
*Wellington (New Zealand).

Currently the network is composed by 16 stations, 6 from the Air Force plus 10 from the NGA (National Geospatial-Intelligence Agency). With this configuration, each satellite is seen from at least three monitor stations,<ref name="GNSS-Book ">J. Sanz Subirana, JM. Juan Zornoza and M. Hernández-Pajares, ''Global Navigation Satellite Systems: Volume I: Fundamentals and Algorithms''</ref> which allows computing more precise orbits and ephemeris data, therefore improving system accuracy.

==The Ground Antennas==
[[File:GPS_infrastructure.png‎|GPS infrastructure in the world|200px|right|thumb]]

The main functions of the Ground Antennas are:
*Send commands, navigation data uploads, and processor program loads to the satellites.
*Collect telemetry.
*Communicate via S-Band and perform S-Band ranging to provide anomaly resolution and early orbit support.

This information can be uploaded to each satellite three times per day, i.e., every 8 hours; nevertheless, it is usually updated just once a day.

The ground antennas are co-located in four of the Monitor stations:
*Ascension Island
*Cape Canaveral
*Diego Garcia
*Kwajalein

In addition, 7 Air Force Satellite Control Network (AFSCN) remote tracking stations are part of the Ground Antennas.

==Control Segment Modernization==
As part of the GPS modernization program, the Air Force has continuously upgraded the GPS control segment for many years. The ground upgrades are necessary to command and control the newer GPS satellites and to enhance cybersecurity.
The Next Generation Operational Control System (OCX) is the future version of the GPS control segment. OCX will command all modernized (GPS III) and legacy GPS satellites, manage all civil and military navigation signals, and provide improved cybersecurity and resilience for the next generation of GPS operations. It will consist of<ref name="OCX">[https://www.gps.gov/systems/gps/control/OCX/ Next Generation Operational Control System (OCX) in GPS official website]</ref>:
*A master control station and alternate master control station
*Dedicated monitor stations
*Ground antennas
*GPS system simulator and
*Standardized space trainer.

OCX development is following an incremental approach.<ref name="OCX"></ref>
*Block 0 is the Launch and Control System (LCS) intended to control Launch and Early Orbit (LEO) operations and the on-orbit checkout of all GPS III satellites. OCX Block 0 is a subset of OCX Block 1 providing the hardware, software, and cybersecurity base for Block 1.
*Block 1 fields the operational capability to control all legacy satellites and civil signals (L1 C/A), military signals (L1P(Y), L2P(Y)) as well as the GPS III satellites and the modernized civil signal (L2C) and the aviation safety-of-flight signal (L5). In addition, Block 1 will field the basic operational capability to control the modernized military signals (L1M and L2M (M-Code)), and the globally compatible signal (L1C). It also fully meets information assurance/cyber defense requirements.
*Block 2 fields the advanced operational capability to control the advanced features of the modernized military signals (L1M and L2M (M-Code)). Block 2 will be delivered concurrently with Block 1.

==Notes==
<references group="footnotes"/>
This article contains some verbatim paragraphs taken from U.S. governmental web pages. Please see the References section.

==References==
<references/>

[[Category:GPS]]
[[Category:GPS Ground Segment]]

Galileo Open Service Navigation Message Authentication

2026-04-17T11:47:20Z

Gema.Cueto: Updated reference ICD/SDD links

{{Article Infobox2
|Category=GALILEO
|Editors=GMV
|Level=Basic
|YearOfPublication=2021
|Logo=GMV
|Title={{PAGENAME}}
}}

Galileo OS-NMA (Open Service – Navigation Message Authentication) represents an [[GNSS Authentication and encryption | authentication]] mechanism that allows a GNSS receiver to verify the authenticity of the GNSS information and of the entity transmitting it, to ensure that it comes from a trusted source. Authentication is an intrinsic GNSS capability remaining internal to the GNSS receiver, without any new interfaces to the avionics.

Galileo OS-NMA will be a free-of-charge service which will become available in the near-term evolutions of the Galileo Full Operational capability (FOC), potentially for 2022-2023. On November 2020, Galileo satellites started the transmission of authentication data for testing purposes<ref>[https://www.gsa.europa.eu/newsroom/news/tests-galileo-osnma-underway Tests of Galileo OSNMA underway(europa.eu)]</ref>. From 2021 Galileo OS-NMA will start a public observation phase before the official provision of Galileo OS-NMA as part of the Galileo services<ref name="OS-NMA">[https://www.euspa.europa.eu/simplecount_pdf/tracker?file=uploads/ucp_2020_open_service_navigation_message_authentication_0.pdf Galileo OS-NMA roadmap]</ref>.

==Introduction to Galileo OS-NMA feature==

Galileo OS-NMA feature consists of digitally signing the [[Galileo Navigation Message | Open Service Navigation message]] in the E1 band, making use of forty reserved bits (“Reserved 1”) in the Galileo E1B data message (I/NAV) and the Timed Efficient Stream Loss-Tolerant Authentication (TESLA) protocol<ref>I. Fernández-Hernández, V. Rijmen, G. Seco-Granados, J. Simon, I. Rodríguez, and J. David Calle, “A Navi-gation Message Authentication Proposal for the Galileo Open Service,” Navigation, Journal of The Institute of Navigation, vol. 63, no. 1, pp. 85-102</ref>, thus keeping the rest of the navigation message unencrypted<ref name="NMA-SIS">[https://www.gsc-europa.eu/sites/default/files/sites/all/files/Galileo-OSNMA-SIS-ICD_in_force.pdf Galileo OS Navigation Message Authentication Specification for Signal-In-Space Testing]</ref> . The use of these reserved bits allows backwards compatibility with older versions of the navigation message ICD.

[[File:Galileo_OS_NMA_SIS.png|500px|OS-NMA field in I/NAV word <ref name="NMA-SIS"/> |none|thumb]]

The OSNMA field is composed of two parts:
* The HKROOT section (first 8 bits) includes the global headers and the Digital Signature Message (DSM).
* The MACK section (next 32 bits) contain the MACs and associated keys, delivered later.

==TESLA protocol==

Galileo OS-NMA authentication capability is based on the use of TESLA protocol. One of the greatest advantages of this protocol is that it requires low bandwidth to transmit the authentication information, together with a tolerance to data loss in case a message is lost.

The main idea of TESLA protocol is that the key used in the authentication process belongs to a chain generated using a one-way function F, also called hash function. The chain starts with a secret seed key; and each element of the chain can be constructed by hashing the previous element. This one-way function cannot be used to predict keys. This implies that the receiver must possess some information (the root key) certified as correct independently from the information sent through the Signal in Space.

The TESLA used for Galileo OS-NMA has been optimized to use a single key for all the satellites, so users will be able to receive the key by any satellite in view. This opens the door to authenticate non-Galileo GNSS satellites.

==Authentication based on Galileo OS-NMA==

The way in which authentication based on Galileo OS-NMA works can be summarized as follows:
* The receiver demodulates the navigation data and a Message Authentication Code (MAC) that authenticates the plaintext navigation message.
* The receiver demodulates the key required to authenticate the MAC. This key is broadcast by the system with some delay with respect the associated MAC.
* The receiver authenticates the key with a previous key from the chain that is considered authentic or from the root key. As explained before, this key is part of a pre-generated one-way chain whose root is public, and which is transmitted in reverse order with respect to its generation
* The receiver re-generates the MAC key with the data, which should match the previously received MAC.

A summary of the proposed Galileo OS-NMA architecture is shown below.

[[File:Galileo_OS_NMA_Architecture.png|700px| Galileo OS-NMA Architecture <ref>[https://www.gsa.europa.eu/sites/default/files/expo/2.4_moises_navarro-gallardo_-_airbus_-_guidelines_os_nma_implementation_in_smartphones.pdf Guidelines OS-NMA implementation in smartphones, Moises Navarro Gallardo, Airbus]</ref> |none|thumb]]

==Credits==
This article has been created based on Galileo Navigation Message Authentication Specification document<ref name="NMA-SIS"/> and other information as indicated through references.

==References==
<references/>

[[Category:GALILEO|!]]

Galileo General Introduction

2026-04-17T11:40:21Z

Gema.Cueto: Updated reference ICD/SDD links

{{Article Infobox2
|Category=GALILEO
|Editors=GMV
|Level=Basic
|YearOfPublication=2025
|Logo=GMV
|Title={{PAGENAME}}
}}
Galileo is Europe’s own global navigation satellite system, providing a highly accurate, guaranteed global positioning service under civilian control. It is inter-operable with others GNSS such as [[GPS General Introduction|GPS]], [[GLONASS General Introduction|GLONASS]] and [[BeiDou General Introduction|BEIDOU]]. Galileo receivers compute their position in the [[GALILEO Reference Frame|Galileo Reference System]] using satellite technology and based on [[An intuitive approach to the GNSS positioning|trilateration principles]].

The Galileo system started its initial services on December 15th, 2016, <ref>[http://europa.eu/rapid/press-release_IP-16-4366_en.htm Galileo goes live!]</ref> and continues to evolve with infrastructure deployment towards Full Operational Capability (FOC).

Galileo system is in constant improvement, leading to a [https://www.esa.int/Applications/Satellite_navigation/Galileo_Second_Generation_enters_full_development_phase Galileo Second Generation (G2)] satellites which will revolutionize the Galileo fleet. G2 satellites are much larger, with significant changes with respect to the first version like the use of electric propulsion, an enhanced antenna with larger radiation area, inter-satellite links between the satellites which will reduce their dependency on the availability of ground installations and the addition of two atomic clocks. Moreover, G2’s fully digital payloads are being designed to be easily reconfigured in orbit, enabling them to actively respond to the evolving needs of users with novel signals and services.<ref>[https://www.esa.int/ESA_Multimedia/Images/2021/05/Galileo_Second_Generation Galileo Second Generation]</ref>

==Introduction==

[[File:Galileo_Art.png‎‎|400px|Galileo Constellation (artistic interpretation)|left|thumb]] Galileo is Europe's Global Navigation Satellite System (GNSS), offering highly accurate, civilian-controlled positioning, navigation, and timing services. Galileo is designed to be fully interoperable with GPS, GLONASS, and BeiDou, providing enhanced reliability and precision. The system operates with a constellation of satellites in Medium Earth Orbit (MEO) at an altitude of 23,222 km, ensuring continuous global coverage. From most locations, six to eight satellites will always be visible <ref>[https://www.euspa.europa.eu/eu-space-programme/galileo/faqs/how-many-satellites-will-galileo-have EUSPA FAQs]</ref>, reaching high values of availability even under challenging conditions. Moreover, Galileo signals are transmitted in four frequency bands (E5a, E5b, E6 and E1), enabling single and dual frequency positioning for users equipped with suitable receivers allowing positions and timing to be determined very accurately to within a few centimetres. As of 2025, Galileo provides positioning accuracy up to 20 cm horizontally and 40 cm vertically.<ref>[https://www.esa.int/Applications/Satellite_navigation/New_Galileo_service_set_to_deliver_20_cm_accuracy ESA, Applications, Satellite Navigation]</ref>

Satellite navigation has become deeply integrated into everyday life, supporting industries and activities that we often take for granted. From personal and transport navigation to precision operations such as autonomous vehicles, GNSS is a critical service. However, the consequences of losing access to these signals would be severe. Truck and taxi drivers, airline crews, and maritime vessels would be unable to navigate effectively. Additionally, financial transactions, telecommunications, and emergency services would be significantly impacted, leading to chaos in public and private sectors. To mitigate such risks, Galileo ensures that satellite navigation remains under civilian authority, giving Europe greater autonomy and control over its satellite-based services. Providing a robust GNSS solution upon the potential unavailability of other GNSS systems.

With the launch and ongoing expansion of Galileo, these risks are greatly reduced. By diversifying the sources of GNSS signals, Galileo offers users a more resilient and reliable navigation service. In addition, its civilian control ensures transparency and accountability, enhancing public trust. Beyond improving basic navigation services, Galileo’s advanced capabilities also support precise timing and synchronization, which are essential for critical sectors such as banking, telecommunications, and scientific research.

The combination of Galileo and [[GPS General Introduction|GPS]] signals ([[Principles of Interoperability among GNSS| GNSS Inter-Operability]]) in dual receivers opens the door to new [[GNSS Applications|GNSS applications]] that require a higher level of precision than currently available with [[GPS General Introduction|GPS]] alone. Examples of these applications are: increase the success rate of rescue operations in the mountains, monitoring of the distribution and dilution of chemicals for agriculture interests, etc.<ref name="EUSPA News archive">[https://www.euspa.europa.eu/newsroom-events/news-archive/galileo-european-satellite-navigation-system-opens-business-opportunities-and-makes-life-easiery EUSPA News archive]</ref>

In addition, Galileo enhances the overall availability and coverage of GNSS signals. For instance, its large constellation of satellites improves signal accessibility in densely populated urban areas, where tall buildings can obstruct signals from satellites low on the horizon.<ref name="European Commission Galileo System">[https://defence-industry-space.ec.europa.eu/eu-space/galileo-satellite-navigation/galileo-system_en European Commission Galileo System]</ref>

With Galileo, Europe is able to exploit the opportunities provided by satellite navigation to the full extent. [[GNSS Receivers General Introduction|GNSS Receivers]] and equipment manufacturers, application providers and service operators benefit from novel business opportunities.<ref name="EUSPA News archive" /><ref name="European Commission Galileo System" />

==History and Development==

As early as the 1990s, the [[Wikipedia:European Union|European Union]] saw the need for Europe to have its own global satellite navigation system.<ref>[https://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:C:1999:221:0001:0003:EN:PDF Council Resolution of 19 July 1999 on the involvement of Europe in a new generation of satellite navigation services -Galileo- Definition phase]</ref>The conclusion to build one was taken in similar spirit to other decisions made in the 1970s to embark on other well-known European endeavours, such as the [https://www.esa.int/Enabling_Support/Space_Transportation/Launch_vehicles/Europe_s_launchers Ariane] launcher and the formation of the Airbus Industrie GIE consortium. The [[Wikipedia:European Union|European Union]] and [https://www.esa.int/ European Space Agency] joined forces to build Galileo, an independent European system under civilian control.

The definition phase and the development and In-Orbit Validation phase of the Galileo program were carried out by the [https://www.esa.int/ European Space Agency] and co-funded by ESA and the [[Wikipedia:European Union|European Union]]. The Full Operational Capability phase of the Galileo program is fully funded by the European Union and managed by the [[Wikipedia:European Commission|European Commission]]. The Commission and the European Space Agency signed a delegation agreement by which ESA acts as design and procurement agent on behalf of the Commission.

The Galileo program was structured according to three main phases<ref name="European Commission Galileo System" />: [[Galileo Future and Evolutions| In-Orbit Validation (IOV), Initial Operational Capability (IOC) and Full Operational Capability (FOC) phases]].

==GALILEO Services==

The Galileo mission and services were elaborated during the initial definition phase in consultation with user communities and the Member States. The high-performance services that the Galileo system offers for users worldwide are the followings:<ref name="Galileo services">[https://www.gsc-europa.eu/galileo/services Galileo services in European GNSS Service Centre portal]</ref>

*[[GALILEO Open Service|Open Service (OS)]]: The freely accessible Open Service targets the mass market and is intended for motor vehicle navigation and location-based mobile telephone services. Free to the user, it provides positioning and synchronization information intended for high-volume satellite radio navigation applications; Galileo Open Service will include in the short term an authentication mechanism through [[Galileo Open Service Navigation Message Authentication|Galileo OS-NMA]].

*[[Galileo High Accuracy Service (HAS)|High Accuracy Service (HAS)]]:The HAS is an open access and free of charge service based on the provision of precise corrections (orbit, clock, biases) transmitted in the Galileo E6 signal (E6-B, data component) as well as via the internet, allowing the user to achieve improved positioning performance. The HAS signal can be encrypted in order to control access to the Galileo HAS services.

*[[Galileo Public Regulated Service (PRS)|Public Regulated Service (PRS)]]: The Public Regulated Service is restricted to government-authorised users, for sensitive applications which require a high level of service continuity. It will be encrypted and designed to be more robust, with anti-jamming mechanisms and reliable problem detection. This service is intended for security and strategic infrastructure (e.g. energy, telecommunications and finance).

*[[Galileo Search and Rescue Service|Search and Rescue Service (SAR)]]: Galileo's worldwide search and rescue service will help to forward distress signals to a rescue coordination centre by detecting emergency signals transmitted by beacons and relaying messages to them.

Later, new services emerged and are currently under development with G2 satellites incorporation. These services are the followings:<ref name="Galileo services" />

*[[Galileo Open Service Navigation Message Authentication|Open Service navigation Message Authentication (OSNMA)]]: Free of charge supplementary service to the Galileo Open Service (OS), designed to enhance the reliability and security of the system. OSNMA ensures that the Galileo navigation messages received by users are authentic, confirming that they originate from the Galileo satellite constellation. By providing this layer of authentication, OSNMA helps protect against spoofing and signal manipulation, offering users greater confidence in the integrity of the data. This is especially crucial for applications requiring high precision and trust, such as aviation, maritime navigation, and critical infrastructure. OSNMA enhances the overall security of Galileo, aligning with Europe’s goal of offering secure and dependable GNSS services under civilian control. The incorporation of G2 satellites improves the robustness of this service, with advanced jamming and spoofing protection mechanisms to safeguard Galileo signals.

*'''Signal Authentication Service (SAS)''': Service which enables an authenticated positioning service by complementing the OSNMA with E6-based ranging authentication capabilities targeting to support civil applications.

*'''Galileo Emergency Warning Satellite Service (EWSS)''': Service which allows national civil protection authorities to rapidly transmit alerts to smartphones (or any Galileo-enabled device) in any place of the globe for enhanced emergency response and resilient risk management. The alert service is independent of the mobile communication infrastructure, and remains operational even when existing systems have been destroyed or are not available (e.g. network saturation or poor mobile network coverage).

*'''Timing Service (TS)''': The Galileo OS offers free positioning and timing/synchronization data. Currently, its timing capabilities are limited to basic determination and dissemination. However, the Galileo Programme has identified the need to expand these features into dedicated, enhanced Timing Services in the Galileo Second Generation. This upgrade will focus on supporting Critical Infrastructure applications by providing features like the Timing service Level Monitoring (TSLM) which consists in monitoring the GST and UTC accuracy.

==GALILEO Architecture==

[[File:Galileo Space Segment.jpg|250px|Galileo Space Segment|right|thumb]]To ensure these Galileo services, a specific architecture is deployed. The Galileo system is divided into three major segments: [[GALILEO Space Segment|Space Segment]], [[GALILEO Ground Segment|Ground Segment]] and [[GALILEO User Segment|User Segment]]. For details see [[GALILEO Architecture|Galileo Architecture]].

The main functions of the [[GALILEO Space Segment|Galileo Space Segment]] are to generate and transmit code and carrier phase signals with a specific [[GALILEO Signal Plan|Galileo signal structure]], and to store and retransmit the navigation message sent by the [[GALILEO Ground Segment|Ground Segment]]. These transmissions are controlled by Passive Hydrogen Masers (PHMs) and Rubidium (RAFS) atomic clocks on board the satellites.

The Galileo satellite system nominal constellation uses a specific layout in space called a 24/3/1 Walker constellation. This means there are 24 main satellites orbiting the Earth at Medium Earth Orbit (MEO), divided into 3 equally spaced orbital planes and completing a full orbit around the Earth in 14 hours. These planes are tilted at 56 degrees from the Equator, allowing the satellites to cover most of the globe. The orbits are spaced 120 degrees apart, ensuring consistent global coverage.

In addition to the main satellites, extra (auxiliary) satellites can also be added. These don't follow the original layout and are placed in other available positions to support the system.

The Galileo constellation consists of over 30 satellites, the majority of which are operational and actively contributing to service provision, while a few may be temporarily unavailable.<ref>[https://www.gsc-europa.eu/system-service-status/constellation-information EUSPA, Constellation Information]</ref>

The [[GALILEO Ground Segment|Ground Segment]] (also referred to as Control Segment) is the responsible for the proper operation of the GNSS system. Its basic functions are:

*To control and maintain the status and configuration of the satellite constellation.
*To predict ephemeris and satellite clock evolution.
*To keep the corresponding GNSS time scale (through atomic clocks).
*To update the navigation messages for all the satellites.

The [[GALILEO Ground Segment|Ground Segment]] constitutes the major system element controlling the entire constellation, the navigation system facilities and the dissemination services. It is composed of two Galileo Control Centres (GCC), each composed of a Ground Control Segment (GCS) and a Ground Mission Segment (GMS).

In one hand, the GCS manages and monitors the satellites and their equipment, as well as planning and automating tasks to ensure everything operates safely and correct. It also supports operations related to the satellite payloads. On the other hand, the GMS determines the navigation and timing data part of the navigation messages.

A worldwide network of ground stations implementing monitoring and control functions are needed for the GCS and GMS. These are the Galileo Sensor Stations (GSS), the Telemetry, Tracking and Control stations (TT&C), and the Galileo Uplink Stations (ULS). The GSS provides Galileo SIS measurements and data to the GCCs. The Telemetry, Tracking and Control stations (TT&C) provide telemetry data and uplinks the control commands required to maintain the Galileo satellites. Finally, the Galileo Uplink Stations (ULS) distribute and uplink the mission data to the Galileo constellation.<ref>[https://www.gsc-europa.eu/galileo/system EUSPA, Galileo System]</ref>

The [[Galileo User Segment|Galileo User Segment]] is composed of [[Galileo Receivers|Galileo Receivers]]. Their main function is to receive Galileo signals, determine pseudoranges (and other observables), and solve the navigation equations to obtain their coordinates and provide a very accurate time.

==Galileo Signal Characteristics==

The Galileo navigation Signals are transmitted in the four frequency bands indicated in the next figure. These four frequency bands are the E5a, E5b, E6 and E1 bands. They provide a wide bandwidth for the transmission of the Galileo Signals.<ref name="Galileo OS Signal In Space ICD">[https://www.gsc-europa.eu/sites/default/files/sites/all/files/Galileo_OS_SIS_ICD_in_force.pdf Galileo OS Signal In Space ICD]</ref>

[[File:Galileo Frequency Plan.png|571px|Galileo Frequency Plan|none|thumb]]

The Galileo frequency bands have been selected in the allocated spectrum for Radio Navigation Satellite Services (RNSS). In addition to that, E5a, E5b and E1 bands are included in the allocated spectrum for Aeronautical Radio Navigation Services (ARNS), employed by Civil-Aviation users, and allowing dedicated safety-critical applications. The names of the Galileo signals are the same as the corresponding carrier frequencies. Note that E5a and E5b signals are part of the E5 bandwidth.<ref name="Galileo OS Signal In Space ICD" />

==GALILEO Performances==

The Galileo [[GNSS Performances|performances]] are different for each service.

For [[GALILEO Open Service|Open Service (OS)]], the positioning accuracy MPLs for SF and DF, and depending on the user location are:

<div style="text-align:center;">
{| class="wikitable" style="display:inline-table;"
|+ style="caption-side:bottom; color:black;"|''[https://www.gsc-europa.eu/sites/default/files/sites/all/files/Galileo-OS-SDD_v1.3.pdf Galileo OS Positioning Accuracy MPLs] at average and worst user location''
! rowspan="2" | GALILEO OS POSITIONING ACCURACY
! colspan="2" | HORIZONTAL ERROR
! colspan="2" | VERTICAL ERROR
|-
! SF
! DF
! SF
! DF
|-
| style="text-align:center;" | Average user location
| ≤ 5m (95%)
| ≤ 5m (95%)
| ≤ 8m (95%)
| ≤ 8m (95%)
|-
|style="text-align:center;" | Worst user location
| ≤ 10m (95%)
| ≤ 10m (95%)
| ≤ 16m (95%)
| ≤ 16m (95%)
|}
</div>

Currently, the [[GALILEO Open Service|Open Service (OS)]] meet these requirements and achieve values of around 1.5 and 2.5 meters (HPE and VPE, correspondingly) for dual frequency combinations (E1/E5a and E1/E5b).

The following figures are an example of the positioning performances achieved during January 2025 (E1/E5a and E1/E5b):

<center>
<gallery widths=350 heights=250>
File:HPE for Galileo E1E5a users in January 2025.png
File:HPE for Galileo 51E5b users in January 2025.png
</gallery>
'''''HPE statistics for Galileo users in January 2025.'''''
</center>
<center>
<gallery widths=350 heights=250>
File:VPE for Galileo E1E5a users in January 2025.png
File:VPE for Galileo E1E5b users in January 2025.png
</gallery>
'''''VPE statistics for Galileo users in January 2025.'''''
</center>

Refer to [https://www.gsc-europa.eu/electronic-library/performance-reports/galileo-open-service-os#:~:text=The%20Galileo%20Open%20Service%20(OS)%20Performance%20Reports%20are,applicable%20Galileo%20Open%20Service%20Service%20Definition%20Document%20(SDD). EUSPA, Galileo Open Service Performance Reports] for quarterly published performance reports of Galileo OS.

The characterisation of Galileo OS in terms of integrity and continuity is currently under development. However, the Probability of SIS Fault and the Probability of Constellation Fault are parameters which help in giving a cofinance at any instantaneous signal. The Probability of SIS Fault is defined as the probability that the instantaneous ranging signal error of a healthy Galileo satellite (excluding atmospheric and receiver errors) exceeds “k” times (being factor “k” the number of standard deviations from the mean corresponding to a probability of Psat in a normal distribution) the Galileo user range accuracy (Galileo URA). And the Probability of Constellation Fault is the probability that the instantaneous ranging signal error of two or more healthy Galileo satellites (also excluding atmospheric and receiver errors) exceeds “k” times the Galileo URA due to a common failure <ref>[https://www.gsc-europa.eu/sites/default/files/sites/all/files/Galileo-OS-SDD_v1.3.pdf Galileo OS SDD]</ref>. The MPLs for these probabilities (factor “k” being 4.17) are defined in the following table:

<div style="text-align:center;">
{| class="wikitable" style="display:inline-table;"
|+ style="caption-side:bottom;"|''Probability of SIS Fault and Probability of Constellation Fault MPLs''
! Parameter
! Value
|-
| style="text-align:center;" | GALILEO PROBABILITY OF SINGLE SIS FAULT (Psat)
| ≤ 3·10−5
|-
| style="text-align:center;" | GALILEO PROBABILITY OF CONSTELLATION N SIS FAULT (Pconst)
| ≤ 2·10−4
|}
</div>

For the [[Galileo High Accuracy Service (HAS)|High Accuracy Service (HAS)]], the MPLs are computed as the RMS over the instantaneous constellation average, for a period of 30 days:

<div style="text-align:center;">
{| class="wikitable" style="display:inline-table;"
|+ style="caption-side:bottom;"|''[https://www.gsc-europa.eu/sites/default/files/sites/all/files/Galileo-HAS-SDD_v1.0.pdf Galileo HAS Accuracy MPLs] for orbit, clock and code biases''
! FIGURE OF MERIT
! MPL – Galileo
! MPL – GPS
|-
| style="text-align:center;" | HAS orbit corrections accuracy
| ≤ 20cm (95%)
| ≤ 33cm (95%)
|-
| style="text-align:center;" | HAS clock corrections accuracy
| ≤ 12cm (95%)
| ≤ 15cm (95%)
|-
| style="text-align:center;" | HAS code biases accuracy
| colspan="2" style="text-align:center;" | ≤ 50cm (95%)
|}
</div>

Currently, the [[Galileo High Accuracy Service (HAS)|Galileo High Accuracy Service (HAS)]] meet these requirements with accuracy values of around 15 and 18 centimetres (Galileo and GPS respectively) for the orbit corrections, 7 and 10 centimetres for the clock corrections, and lower than 40 centimetres (both Galileo and GPS) for the code biases.

The following figures are an example of the accuracy achieved during the period from January 2025 to March 2025 (only Galileo):

<center>
<gallery widths=350 heights=150>
File:HAS accuracy of the Galileo orbit corrections.png|'''''HAS accuracy of the Galileo orbit corrections'''''
File:HAS accuracy of the Galileo clock corrections.png|'''''HAS accuracy of the Galileo clock corrections'''''
File:HAS accuracy of the Galileo code biases.png|'''''HAS accuracy of the Galileo code biases'''''
</gallery>
</center>

Refer to [https://www.gsc-europa.eu/electronic-library/performance-reports/galileo-high-accuracy-service-has EUSPA, Galileo HAS Performance Reports] for quarterly published performance reports of Galileo HAS.

Current Galileo SAR Service performance can be expressed in terms of MPLs for the contribution to the SAR Forward and Return link services as it is indicated in the [https://www.gsc-europa.eu/sites/default/files/sites/all/files/Galileo-SAR-SDD.pdf Galileo SAR Service Definition document].

The SAR MPLs are divided into SAR/Galileo Forward Link Service, SAR/Galileo Return Link Service, and SAR/Galileo Space Availability:

<div style="text-align:center;">
{| class="wikitable" style="display:inline-table;"
! SAR/GALILEO FORWARD LINK SERVICE
! style="text-align:center;" | TARGET VALUE
|-
| style="text-align:center;" | Forward Link Service Availability
| style="text-align:center;" | >99%
|-
| style="text-align:center;" | European MEOLUT Facility availability in Nominal mode
| style="text-align:center;" | >95%
|-
| style="text-align:center;" | European MEOLUT Facility availability in Degraded mode
| style="text-align:center;" | >97.5%
|-
| style="text-align:center;" | Detection probability: Valid Message
| style="text-align:center;" | >99%
|-
| style="text-align:center;" | Location probability within 5km (1–12 Bursts)
| style="text-align:center;" | >95%
|-
| style="text-align:center;" | Location probability within 5km (Single Burst)
| style="text-align:center;" | >90%
|-
| style="text-align:center;" | Location probability (Single Burst)
| style="text-align:center;" | >90%
|-
| style="text-align:center;" | Location probability (1–12 Bursts)
| style="text-align:center;" | >98%
|-
| style="text-align:center;" | Location probability within 2km (1–12 Bursts)
| style="text-align:center;" | >90%
|}
</div>

<div style="text-align:center;">
{| class="wikitable" style="display:inline-table;"
! SAR/GALILEO RETURN LINK SERVICE
! style="text-align:center;" | TARGET VALUE
|-
| style="text-align:center;" | Return Link Service Availability
| style="text-align:center;" | >95%
|-
| style="text-align:center;" | End-to-end Return Link Service Availability
| style="text-align:center;" | >90%
|-
| style="text-align:center;" | Galileo System Message Delivery Latency within 15 minutes
| style="text-align:center;" | >99%
|-
| style="text-align:center;" | End-to-end Message Delivery Loop Latency within 30 minutes
| style="text-align:center;" | >95%
|}
</div>

<div style="text-align:center;">
{| class="wikitable" style="display:inline-table;"
|+ style="caption-side:bottom;"|''[https://www.gsc-europa.eu/sites/default/files/sites/all/files/Galileo-SAR-SDD.pdf Galileo SAR MPLs]''
! SAR/GALILEO SPACE AVAILABILITY
! style="text-align:center;" | TARGET VALUE
|-
| style="text-align:center;" | SAR Repeater Availability
| style="text-align:center;" | >95%
|}
</div>

The SAR MPLs are currently mostly meet but variates with the location and the month. MPL fulfilment status dashboards for Detection and Location, Space Segment Availability, and Ground Segment Availability are published for each quarter of the year at the [https://www.gsc-europa.eu/electronic-library/performance-reports/search-and-rescue-sar-galileo-service EUSPA, Galileo SAR Performance Reports].

In the case of the [[Galileo Public Regulated Service (PRS)|Galileo Public Regulated Service (PRS)]], the [[GNSS Performances|performance]] requirements include horizontal and vertical [[Accuracy|accuracy]]. The [[Availability|availability]] of the service should be 99.5%.

See the article [[Galileo Performances|Galileo Performances]] for further information.

==Credits==
Edited by GMV, using information from ESA, European GNSS Service Centre and European Union as indicated through the references.

==Notes==
<references group="footnotes"/>
==References==
<references/>

[[Category:GALILEO|!]]

Galileo User Segment

2026-04-17T11:36:54Z

Gema.Cueto: Updated reference ICD/SDD links

{{Article Infobox2
|Category=GALILEO
|Editors=GMV
|Level=Basic
|YearOfPublication=2011
|Logo=GMV
|Title={{PAGENAME}}
}}
The [[GALILEO General Introduction|Galileo]] System is an independent, global, European-controlled, satellite-based navigation system and provides a number of guaranteed services to users equipped with Galileo-compatible receivers.

The Galileo system is divided into three major segments: [[GALILEO Space Segment|Space Segment]], [[GALILEO Ground Segment|Ground Segment]] and [[GALILEO User Segment|User Segment]]. The Galileo User Segment is composed by all the compatible receivers and devices which collect the Galileo signals, determine pseudoranges (and other observables), and [[An intuitive approach to the GNSS positioning|solve the navigation equations]] in order to obtain their coordinates and provide accurate time synchronization. There are different user’s communities depending on the application and covering a wide range, from transport to timing applications.

Basic elements of a generic [[GNSS Receivers General Introduction|GNSS Receiver]] are an antenna with pre-amplification, an L-band radio frequency section, a microprocessor, an intermediate-precision oscillator, a feeding source, some memory for data storage, and an interface with the user. The calculated position is referred to the antenna phase centre.

==Galileo Receivers==
A [[GALILEO Receivers|Galileo Receiver]] is a device capable of determining the user position, velocity and precise time (PVT) by processing the signal broadcasted by Galileo satellites.

Any [[An intuitive approach to the GNSS positioning|navigation solution]] provided by a [[GNSS Receivers General Introduction|GNSS Receiver]] is based on the computation of its distance to a set of satellites, by means of extracting the propagation time of the incoming signals traveling through space at the speed of light, according to the satellite and receiver local clocks. Notice that satellites are always in motion, so previous to obtaining the navigation message, the satellite’s signal is detected and tracked. The receiver’s functional blocks that perform these tasks are the antenna, the front-end and the baseband signal processing (in charge of acquiring and tracking the signal).<ref name="GNSS-Book ">J. Sanz Subirana, JM. Juan Zornoza and M. Hernández-Pajares, ''Global Navigation Satellite Systems: Volume I: Fundamentals and Algorithms''</ref>

Once the signal is acquired and tracked, the receiver application decodes the navigation message. The navigation data contain all the parameters that enable the user to perform positioning service. The types of data needed to perform positioning are:<ref name = "Galileo-OS-SDD">[https://www.gsc-europa.eu/sites/default/files/sites/all/files/Galileo-OS-SDD_in_force.pdf Applicable Galileo Open Service –Service Definition Document]</ref>
# Ephemeris which are needed to compute the position of the satellite to the user receiver.
# Time and clock correction parameters which are needed to compute satellite clock offsets and time conversions.
# Service parameters with satellites health.
# The ionospheric parameters model, needed for single-frequency users.
# Almanac which allow less precise computation of the position of all the satellites in the constellation to facilitate the initial acquisition of the signals by the receiver

For single frequency receivers, the Broadcast Group Delays are also needed.

In 2010 there were only three chipset manufacturers producing Galileo-ready products. Since them, the market has been evolving, and today it is ready for Galileo. The list of Galileo compatible devices that are available today can be found at the following reference <ref name = "Use Galileo">[https://www.usegalileo.eu/EN/ UseGalileo.eu website]</ref>.

==Service Centers==
The European [[GNSS Service Centre]] (GSC) aims at providing a single interface between the Galileo system and the Galileo Open Service (OS) and High Accuracy Service (HAS) users for the provision of specific services beyond the signal in space transmitted by the satellites. The GSC assures knowledge sharing, custom performance assessment, dissemination of information and support to the provision of value-added services which are enabled by the Galileo OS and HAS core services<ref name = "Galileo-OS-SDD"></ref>:
[[File:Galileo_User_Segment_GSC.png|300px|Overall context of the GSC|thumb]]
The GSC functionality and services when fully developed will cover the followings<ref name = "Galileo-OS-SDD"></ref>:
*Helpdesk support which is intended to answer questions from OS users on Galileo OS SIS, GSC OS Support Services and from OS receiver and developers of applications.
*Information regarding the Galileo system status (Galileo Almanacs and ephemeris, constellation status and provision of Galileo Service Notices)
*Notifications to users’ publication which includes general information on the constellation and space vehicle status (published by means of Notice Advisory to Galileo Users messages – NAGUs) and also reports related to Galileo Open Service navigation performance indicators and the GSC performances.
*Programme Reference documentation and general information included in an Electronic Library.
*Interface with GNSS Service providers.
*Support on topics like GNSS Simulation and Testing Infrastructure (GSTI) for the GNSS developers.
*The user satisfaction monitoring regarding Galileo (meaning customised performance assessments, reporting for specific communities and support regarding Galileo services development for different communities and domains)

==Applications==
The European Commission is committed to 6 priority domains identified in the impact assessment accompanying its Action Plan on [[GNSS Applications|GNSS Applications]]:<ref>[http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=SEC:2010:0716:FIN:EN:PDF Impact Assesment: Action Plan on Global Navigation Satellite System (GNSS) Applications]</ref>
* applications for individual handsets and mobile phones (LBS);
* road transport;
* aviation;
* maritime transport;
* precision agriculture and environment protection;
* civil protection and surveillance.
Examples of applications in which Galileo can play a role are detailed in Galileo GSC [https://www.gsc-europa.eu/galileo-gsc-overview/applications website] and devices that implement Galileo can be found on the ”Use Galileo” website from the [https://www.gsc-europa.eu/galileo-gsc-overview/applications GSA]<ref name = "Use Galileo">[https://www.usegalileo.eu/EN/ UseGalileo.eu website]</ref>.

<gallery>
Image:app_transport.png
Image:app_agriculture.png
Image:app_survey.jpg
</gallery>

==Credits==
The information provided in this article has been compiled by GMV. In some cases, tables and paragraphs have been extracted from the indicated references, in particular from the ''European GNSS Service Centre (GSC)'' [https://www.gsc-europa.eu/ website].
<references group="footnotes"/>
==References==
<references/>

[[Category:GALILEO]]
[[Category:GALILEO Architecture]]
[[Category:GALILEO User Segment]]

Galileo Space Segment

2026-04-17T11:33:08Z

Gema.Cueto: Updated reference ICD/SDD links

{{Article Infobox2
|Category=GALILEO
|Editors=GMV
|Level=Basic
|YearOfPublication=2011
|Logo=GMV
|Title={{PAGENAME}}
}}

The Galileo constellation comprises of 30 satellites placed in MEO orbit, with 10 satellites placed in each of 3 orbital planes (at 56º nominal inclination <ref name="Galileo_Early_Services">[https://www.gsc-europa.eu/galileo/system Galileo System in European GNSS Service Centre website]</ref>) distributed evenly round the equator. The active constellation comprises of 24 satellites (Walker 24/3/1), including 6 spare satellites, which can be moved to replace any failed satellite within the same plane, thereby reducing the impact of failures upon quality of service. All satellites are identical in terms of design, performance capability and fuel load. Each satellite broadcasts navigation timing signals together with navigation data providing the clock and ephemeris correction data which are essential for navigation.<ref name="Galileo_Early_Services">[https://www.gsc-europa.eu/galileo/system Galileo System in European GNSS Service Centre website]</ref>

The nominal orbit of a Galileo satellite is circular, with an altitude of approximately 23,229 km above the Earth’s surface. This configuration results in a ground track that repeats every 10 days, corresponding to 17 orbital revolutions over nearly ten sidereal days.

==Constellation features==
[[File:Galileo Space Segment.jpg|left|thumb|400px|Galileo Space Segment]]
The altitude of the satellites has been chosen to avoid gravitational resonances so that, after initial orbit optimisation, station-keeping manoeuvres will not be needed during the lifetime of a satellite. The altitude chosen also ensures a high visibility of the satellites.

The position constraints for individual satellites are set by the need to maintain a uniform constellation, for which it is specified that each satellite should be within +/- 2° of its nominal position relative to the adjacent satellites in the same orbit plane and should be within 2° of the orbit plane.

The in-plane accuracy is equivalent to a relative tolerance of over 1000 km but requires very careful adjustment of the satellite velocity to ensure that the orbit period of all the satellites is kept precisely the same. The across-track tolerance allows the inclination and Right Ascension of the Ascending Node (RAAN) of each satellite to be biased at launch so that natural drifts remain within the tolerance without the need for orbit plane changes requiring major expense of fuel.

The spare satellite in each orbit plane ensures that in case of failure the constellation can be repaired quickly by moving the spare to replace the failed satellite. This could be done in a matter of days, rather than waiting for a new launch to be arranged which could take many months. The satellites are designed to be compatible with a range of launchers providing multiple and dual launch capabilities.

There are good reasons for choosing such a structure for the Galileo constellation. With 30 satellites at such an altitude, there is a very high probability (more than 90%) that anyone anywhere in the world can always be in sight of at least four satellites and hence is able to determine their position from the ranging signals broadcast by the satellites. The inclination of the orbits was chosen to ensure good coverage of polar latitudes, which are poorly served by the US GPS system.

From most locations, six to eight satellites may always be visible, allowing positions to be determined very accurately – to within a few centimeters. Even in high rise cities, there is a good chance that a road user may have sufficient satellites overhead for taking a position, especially as the Galileo system is interoperable with the US system of 24 GPS satellites.

This constellation provides good local geometries with a typical vertical dilution of precision (VDOP) of 2.3 and horizontal dilution of precision (HDOP) around 1.3. An additional benefit of the constellation geometry is the limited number of planes, which allows for faster deployment and reduced constellation maintenance costs due to the capability to launch multiple satellites with a single launcher.

==Galileo satellites==
[[File:Galileo satellite system.jpg|right|thumb|300px|Galileo satellite]]

The Galileo constellation is composed of a total of 30 Medium Earth Orbit (MEO) satellites, of which 6 are spares. Each satellite broadcasts precise time signals, ephemeris and other data. The Galileo satellite constellation has been optimised to the following nominal constellation specifications:<ref name="OS SDD"> [https://www.gsc-europa.eu/sites/default/files/sites/all/files/Galileo-OS-SDD_in_force.pdf Applicable galileo Open Service (OS) Service Definition Document (SDD)]</ref>

*circular orbits (satellite altitude of 23 222 km)
*orbital inclination of 56°
*three equally spaced orbital planes
*eight operational satellites, equally spaced in each plane
*six spare satellites (also transmitting)

The constellation is complemented by spare satellites that can be repositioned to any given slot depending on maintenance or service evolution needs. The location of the spare satellites in each plane is not yet frozen and will be decided at the time of deployment of the spare capability.<ref name="OS SDD"> [https://www.gsc-europa.eu/sites/default/files/sites/all/files/Galileo-OS-SDD_in_force.pdf Applicable galileo Open Service (OS) Service Definition Document (SDD)]</ref>

Each Galileo satellite is a 700 kg/1600 W class satellite, contains all the equipment needed to perform its assigned navigation and timing tasks over the course of its 12-year design life. Powered by solar arrays, with its internal components carefully shielded against the radiation prevailing in medium-Earth orbit.

The image shows an artist's impression of a Galileo spacecraft in orbit with solar arrays deployed. The spacecraft rotates about its Earth-pointing axis so that the flat surface of the solar arrays always faces the Sun to collect maximum solar energy. The antennas, shown on the underside of the body in the picture, always point towards the Earth. The spacecraft body will measure 2.7 m x 1.1 m x 1.2 m and the deployed solar arrays span 13 m.

===Galileo Satellite subsystems===
The satellite is composed of the following subsystems:
*Payload Subsystem including the navigation payload and the SAR payload
*Structure Subsystem
*Thermal Control Subsystem (TCS)
*Electrical Power Subsystem (EPS) with the following units:
**Solar Arrays (SA)
**Solar Array Drive Mechanisms (SADM)
**Battery
**Power Conditioning and Distribution Unit (PCDU)
*Harness
*Avionics Subsystem with
**on-board computer (Integrated Control and Data Handling Unit, ICDU)
**Attitude and Orbit Control System, AOCS (based on earth sensors, sun sensors, gyros, reaction wheels and magnetic torquers),
**Software (SW)
*Telemetry, Tracking and Command (TTC) Subsystem (with S-Band Transponder and two low-gain, omni-directional antennas)
*Propulsion Subsystem (mono-propellant system with one tank and 8 thrusters)
*Laser Retro-Reflector (LRR)
*Platform Security Unit (PFSU)

===Galileo Satellite components===
The '''L-band antenna''' transmits the navigation signals in the 1200-1600 MHz frequency range.

The '''[[Galileo Search and Rescue Service|SAR (Search and Rescue) antenna]]''' picks up distress signals from beacons on Earth and transmits them to a ground station for forwarding to local rescue services.

The '''C-band antenna''' receives signals containing mission data from Galileo Uplink Stations. This includes data to synchronise the on-board clocks with a ground-based reference clock and integrity data which contains information about how well each satellite is functioning. The integrity information is incorporated into the navigation signal for transmission to users.

Two '''S-band antennas''' are part of the telemetry, tracking and command subsystem. They transmit housekeeping data about the payload and spacecraft to ground control and, in turn, receive commands to control the spacecraft and operate the payload. The S-band antennas also receive, process and transmit ranging signals that measure the satellite's altitude to within a few metres.

The '''infrared Earth sensors''' and the '''Sun sensors''' both help to keep the spacecraft pointing at the Earth. The infrared Earth sensors do this by detecting the contrast between the cold of deep space and the heat of the Earth's atmosphere. The Sun sensors are visible light detectors which measure angles between their mounting base and incident sunlight.

The '''laser retro-reflector''' allows the measurement of the satellite's altitude to within a few centimetres by reflecting a laser beam transmitted by a ground station. The laser retro-reflector is used only about once a year, as altitude measurements via S-band antenna ranging signals are otherwise accurate enough.

The '''space radiators''' are heat exchangers that radiate waste heat, produced by the units inside the spacecraft, to deep space and thus help to keep the units within their operational temperature range.

In the following image are identified the main external components: <ref name = "Satellite anatomy">[https://www.esa.int/Applications/Navigation/Galileo/Satellite_anatomy "Satellite anatomy”, ESA] </ref>

[[File:ExternalPartsGalileoSatellite.png | none|thumb|400px| Source: "Satellite anatomy”, ESA<ref name = "Satellite anatomy">[https://www.esa.int/Applications/Navigation/Galileo/Satellite_anatomy "Satellite anatomy”, ESA] </ref>]]

===Interior: payload===
The Galileo satellites include two payloads, the Navigation payload and the Search and Rescue payload.
Their main functions are:
*Provision of on-board timing signals
*Receipt & storage of up-linked navigation message data
*Receipt & storage of up-linked integrity data
*Assembly of navigation message in the agreed format
*Error correction coding of navigation message
*Generation of ranging codes
*Encryption of ranging codes as required
*Generation and modulation of L-Band carrier signals
*Broadcast of navigation signals

The timing signals are provided by high precision on-board clocks, implemented as two (cold) redundant pairs per satellite, each pair including two different technologies, both of them being operated simultaneously:

A '''Passive Hydrogen Maser (PHM) clock''' is the master clock on board the spacecraft. It is an atomic clock which uses the ultra stable 1.4 GHz transition in a hydrogen atom to measure time to within 0.45 ns over 12 hours.

A '''Rubidium Atomic Frequency Standard (RAFS) clock''' will be used should the maser clock fail. It is accurate to within 1.8 ns over 12 hours.
[[File:Rubidium_clock.jpg|left|thumb|250px|Rubidium clock]]

At any time, only one clock of each type is operating. Under normal conditions, the operating maser clock produces the reference frequency from which the navigation signal is generated. Should the maser clock fail, however, the operating rubidium clock will take over instantaneously and the two reserve clocks will start up. If the problem with the failed maser clock is unique to that clock, the second maser clock will take over from the rubidium clock after a few days when it is fully operational. The rubidium clock will then go on stand-by or reserve again. In this way, by having four clocks, the Galileo spacecraft is guaranteed to generate a navigation signal at all times.

The '''clock monitoring and control unit''' provides the interface between the four clocks and the navigation signal generator unit (NSGU). It passes the signal from the active master clock to the NSGU and also ensures that the frequencies produced by the master clock and the active spare are in phase, so that the spare can take over instantly should the master clock fail.

The '''navigation signal generator, frequency generator and up-conversion units''' are in charge of generating the navigation signals using input from the clock monitoring unit and the up-linked navigation and integrity data from the C-band antenna. The navigation signals are converted to L-band for broadcast to users.

The '''navigation signal generator, frequency generator and up-conversion units (NSGU)''', which includes internal cold redundancy, receives the up-linked navigation data and uses them to generate the navigation signals in the appropriate format, performs the PRN encoding and the modulation of the 3 navigation signals (E5a + E5b, E6 and L1) and passes them to the Frequency Generation and Up-conversion Unit (FGUU) which performs the up- conversion into L-band of the 3 signals.

The '''remote terminal unit''' is the interface between all the payload units and the on-board computer.

===Interior: service module===
'''SADM''' is the drive mechanism that connects the solar arrays to the spacecraft and rotates them slowly so that the surface of the arrays can remain perpendicular to the Sun's rays at all times.

The '''gyroscopes''' measure the rotation of the spacecraft.

The '''reaction wheels''' control the rotation of the spacecraft. When they rotate, so does the spacecraft. It rotates twice per orbit to allow the solar arrays to remain parallel to the Sun's rays.

The '''magneto bar''' modifies the speed of rotation of the reaction wheels by introducing a torque (turning force) in the opposite direction.

The '''power conditioning and distribution unit''' regulates and controls power from the solar arrays and batteries and distributes it to all the spacecraft's subsystems and payload.

The '''environmental monitoring unit''' on-board takes radiation measurements.

The '''on-board computer''' controls all aspects of spacecraft and payload functioning.

=== Satellites Key Features<ref>[https://www.ohb-system.de/files/images/mediathek/downloads/190603_OHB-System_Galileo_FOC-Satellites_2019-05.pdf Key Features of the Galileo Satellites], OHB</ref> ===

{| class="wikitable"
|-
! colspan="2" | Key Features
|-
|Body dimensions || 2.5 x 1.2 x 1.1 m
|-
|Span solar generator || 14.67 m
|-
|Solar generator power || 1.9 Kw
|-
|Navigation signals || 3 bands (E5, E6, E1)
|-
|SAR Transponder || UHF Receiver 406 MHz
L-Band transceiver 1,544 MHz
|-
|Lifetime || > 12 years on-orbit
> 5 years ground storage
|-
|Reliability || > 0.88 /12 years
|-
|Launch mass || 732.8 Kg
|}

==Galileo Metadata ==
The Galileo Metadata can be found in the GNSS Service Centre Web Page. See the following link:

https://www.gsc-europa.eu/support-to-developers/galileo-satellite-metadata

==Satellites Names and Launching ==

Up to date information on the Galileo program, namely launching and phases can be found in: <ref>[https://www.gsc-europa.eu/system-service-status/constellation-information Current Galileo constellation status] </ref>.

European Commission created a children's drawing competition to name each launched satellite. The competition was open to children from all member states and the name of the winner from each state was given to one of the Galileo satellites.

The full list of the winners competition can be found [http://ec.europa.eu/enterprise/policies/satnav/galileo/drawing-competition/index_en.htm here], as well the drawings that gave them the victory.

More information on the Galileo IOV satellites is provided [https://ec.europa.eu/growth/sectors/space/galileo/drawing-competition_en| here].

==References==
<references/>

[[Category:GALILEO]]
[[Category:GALILEO Architecture]]
[[Category:GALILEO Space Segment]]

Reference Frames in GNSS

2026-04-17T11:25:41Z

Gema.Cueto: Updated reference ICD/SDD links

{{Article Infobox2
|Category=Fundamentals
|Authors=J. Sanz Subirana, J.M. Juan Zornoza and M. Hernández-Pajares, Technical University of Catalonia, Spain.
|Level=Basic
|YearOfPublication=2011
|Title={{PAGENAME}}
}}
Brief descriptions of GPS WGS-84, GLONASS PZ-90, Galileo GTRF and BeiDou Coordinate System (BDC) reference frames are provided as follows.

== [[GPS General Introduction|GPS]] reference frame WGS-84 ==

From 1987, GPS uses the World Geodetic System WGS-84, developed by the US Department of Defense (DoD) and now maintained by the US National Geospatial Intelligence Agency (NGA). WGS-84, is a unified terrestrial reference system for position and vector referencing <ref group="footnotes">The document "Modern Terrestrial Reference Systems PART 3: WGS-84 and ITRS" contains data and interesting references about WGS-84 and ITRS (http://www.ngs.noaa.gov/CORS/Articles/Reference-Systems-Part-3.pdf).</ref>. Indeed, the GPS broadcast ephemeris are linked to the position of the satellite antenna phase centre in the WGS-84 reference frame. Thus, the user receiver coordinates will be expressed in the same ECEF frame.

The initial implementation of WGS-84 was realized from a set of more than a thousand terrestrial sites, which coordinates were derived from Transit observations <ref group="footnotes">With accuracy at the level of 1-2 meters, while the accuracy of the ITRF reference stations is at the centimetre level.</ref>. Successive refinements (which also leaded to some adjustments of the fundamental constants), using more accurate coordinates of the monitor stations, approximate to some ITRS realizations. For instance, realizations WGS84(G730) <ref group="footnotes">"G" indicates that it has exclusively been obtained with GPS observations and 730 indicates the GPS week.</ref> and WGS84(G873) correspond to ITRF92 and ITRF94, respectively. The refined frame WGS84(G1150) was introduced in 2002, which agrees with ITRF2000 at the centimetre level. The most recent version is WGS-84 (G1762 <ref>[https://epsg.io/7664 WGS-84 (G1762) Information]</ref>) and was implemented on October 2013 and is aligned to the International GNSS Service (IGS) realisation of the ITRF2008<ref name="NGA">[https://earth-info.nga.mil/GandG/publications/NGA_STND_0036_1_0_0_WGS84/NGA.STND.0036_1.0.0_WGS84.pdf National Geospatial-Intelligence Agency (NGA) Standardization Document World Geodetic System 1984]</ref>.

The parameters of the WGS-84 ellipsoid are given in the following table 1:

::[[File:WGS84_Table.png|none|thumb|640px|'''''Table 1:''''' Ellipsoidal parameters WGS-84 (revised in 1997) and also in NGA Standard<ref name="NGA">[https://earth-info.nga.mil/GandG/publications/NGA_STND_0036_1_0_0_WGS84/NGA.STND.0036_1.0.0_WGS84.pdf National Geospatial-Intelligence Agency (NGA) Standardization Document World Geodetic System 1984]</ref>.]]

== [[GLONASS General Introduction|GLONASS]] reference frame PZ-90 ==

The GLONASS broadcast ephemeris are given in the Parametry Zemli 1990 (Parameters of the Earth 1990) (PZ-90) reference frame. As the WGS-84, this is an ECEF frame with a set of fundamental parameters associated (see table 2 from [GLONASS ICD, 2020]<ref name=GLONASS_ICD_2020>[https://glonass-iac.ru/upload/docs/stehos/stehos_en.pdf GLONASS ICD, 2020]</ref>).

The determination of a set of parameters to transform the PZ-90 coordinates to the ITRF97 was the target of the International GLONASS Experiment (IGEX-98). [Boucher and Altamimi, 2001] <ref>[Boucher and Altamimi, 2001] Boucher, C. and Altamimi, Z., 2001. ITRS, PZ-90 and WGS 84: current realizations and the related transformation parameters. Journal of Geodesy 75, pp. 613-619.</ref>presents a review of the IGEX-98 experiment and, as a conclusion, they suggest the following transformation <ref group="footnotes"><math>mas:</math> mili-arcseconds (<math>1 mas = 4.84813681 \cdot
10^{-9}</math> radians). <math>ppb:</math> parts per billion (<math>1 ppb=10^{-9}</math>).</ref> from <math>(x,y,z)</math> in PZ-90 to <math>(x',y',z')</math> in WGS-84, with a meter level of accuracy.

::<math>
\left [
\begin{array}{c}
x'\\
y'\\
z'\\
\end{array}
\right ]
=
\left [
\begin{array}{c}
x\\
y\\
z\\
\end{array}
\right ]
+
\left [
\begin{array}{ccc}
-3\,ppb & -353\,mas & -4\,mas\\
353\,mas & -3\,ppb & 19\,mas\\
4\,mas & -19\,mas & -3\,ppb\\
\end{array}
\right ]
\left [
\begin{array}{c}
x\\
y\\
z\\
\end{array}
\right ]
+
\left [
\begin{array}{c}
0.07\,m\\
-0.0\,m\\
-0.77\,m\\
\end{array}
\right ] \qquad\mbox{(1)}</math>

Following the notation of equation (3) in [[Transformation between Terrestrial Frames]]:

::<math>
\left (
\begin{array}{c}
x\\
y\\
z\\
\end{array}
\right )_{_{TRF2}}
=
\left (
\begin{array}{c}
x\\
y\\
z\\
\end{array}
\right )_{_{TRF1}}
+
\left (
\begin{array}{c}
T_1\\
T_2\\
T_3\\
\end{array}
\right )
+
\left (
\begin{array}{ccc}
D & -R_3 & R_2\\
R_3 & D & -R_1\\
-R_2 & R_1 & D\\
\end{array}
\right )
\left (
\begin{array}{c}
x\\
y\\
z\\
\end{array}
\right )_{_{TRF1}}</math>

the previous transformation (1) is defined by the parameters table:

::[[File:GLONASS_Table.png|none|thumb|400px]]

According to the GLONASS modernisation plan<ref>[http://gpsworld.com/directions-2014-new-horizons-of-glonass/ Directions 2014: New Horizons of GLONASS], GPS World, Denis Lyskov, Deputy Head of the Russian Space Agency, Roscosmos, December 1, 2013</ref>, the ephemeris information implementing the PZ-90.11 reference system was updated on all operational GLONASS satellites starting from 3:00 pm on December 31, 2013<ref>[https://glonass-iac.ru/upload/docs/stehos/stehos_en.pdf GLONASS Open Service Performance Standard ]</ref>. From this time on, the satellites are broadcasting in the PZ-90.11<ref>[http://www.glonass-iac.ru/en/content/news/?ELEMENT_ID=721 The transition to using the terrestrial geocentric coordinate system PZ-90.11 in operating GLONASS system has been implemented], Russian Federal Space Agency, Information-analytical centre, 4 April 2014</ref>. This ECEF reference frame is an updated version of PZ-90, closest to the ITRF2000.

The transformation from PZ-90.11 to ITRF2008 contains only an origin shift vector, and no rotations nor scale factor, as it is shown in equation (2) [Revnivykh, 2007]<ref>[Revnivykh, 2007] Revnivykh, S., 2007. GLONASS Status and Progress. In:
Minutes of the 47th CGSIC Meeting, Forth Worth, Texas.</ref><ref>[http://www.oosa.unvienna.org/pdf/icg/2012/template/PZ90-02_v2.pdf Global Geocentric Coordinate System Of The Russian Federation], WG D – Reference Frames, Timing and Applications, Mr. V. Vdovin and Ms. A. Dorofeeva, November 7, 2012.</ref>

::<math>
\left [
\begin{array}{c}
x\\
y\\
z\\
\end{array}
\right ]_{ITRF2008}
=
\left [
\begin{array}{c}
x\\
y\\
z\\
\end{array}
\right ]_{PZ-90.11}
+
\left [
\begin{array}{r}
0.003\,m\,\pm0.002\,m\\
0.001 \,m\,\pm0.002\,m\\
0.001 \,m\,\pm0.002\,m\\
\end{array}
\right ] \qquad\mbox{(2)}</math>

The parameters associated to the PZ-90 and PZ-90.11 are given in the next table 2 ([GLONASS ICD, 1998]<ref>[https://www.unavco.org/help/glossary/docs/ICD_GLONASS_4.0_(1998)_en.pdf GLONASS ICD, 1998]</ref> and [GLONASS ICD, 2020]<ref name=GLONASS_ICD_2020/>):

::[[File:PZ90_Table.png|none|thumb|640px|'''''Table 2:''''' Ellipsoidal parameters of PZ-90 and PZ-90.11.]]

== [[GALILEO General Introduction|Galileo]] Terrestrial Reference Frame (GTRF) ==

Next subsections provide an overview of the first realizations of Galileo Terrestrial Reference Frame, together with a description of the current applicable reference frame.

=== First Galileo Reference Frames ===

A consortium named the Galileo Geodetic Service Provider (GGSP<ref>[https://www.gsa.europa.eu/implementation-galileo-geodesy-service-provider-prototype Galileo Geodetic Service Provider in GSA website]</ref>), consisting of seven institutions under the lead of GeoForschungsZentrum Potsdam, built up a prototype for the development of the Galileo Terrestrial Reference Frame (GTRF) and the establishment of a service with products and information for the potential users under an EC 6th framework contract.

Like GPS, Galileo established a dedicated terrestrial reference frame (GTRF) as an independent realization of the international terrestrial reference system ITRS based on the estimated coordinates for each one of the Galileo Sensor Station (GSS) sites. According to Galileo requirements the three-dimensional differences of the position compared to the most recent ITRF should not exceed 3 cm (2-sigma).

Operational GTRF includes all Galileo sensor stations (GSS) and selected stations of IGS. IGS stations are used for alignment to ITRF (as GSS are not a part of it) and for densification of the network to improve the accuracy of the results.

GTRF computation includes two parts: free network adjustment including all stations (GSS and selected IGS) and network alignment to ITRF using the IGS stations.

Under GGSP project, the four first realizations of GTRF were established:

::::[[File:GTRF_Fig_1.png|none|420px]]

The network included 131 IGS stations and 13 GESS (Galileo Experimental Sensor Stations for the GIOVE mission).

::::[[File:GTRF_Fig_2.png|none|580px]]

Already the initial realization of the GTRF called GTRF07v01 was in agreement with ITRF05 up to 0.9, 0.9 and 2.7 mm for North, East, and Up respectively.

The anticipated configuration of the operational GTRF network is presented in the figure below.

::::[[File:GTRF_Fig_3.png|none|580px]]

GTRF transformation parameters to ITRF2005 are reported below.

Solution GTRF08v01, epoch 07:241, used number of ITRF2005 sites: 103

::::[[File:GTRF_Fig_4.png|none|420px]]

=== Current Galileo Terrestrial Reference Frame ===

Based on the outcomes of the previous section, the Galileo Terrestrial Reference Frame used by the Galileo system is described in the Galileo Open Service - Service Definition Document (SDD) <ref>[https://gssc.esa.int/navipedia/index.php/Galileo_Open_Service_(OS) Galileo Open Service - Service Definition Document (SDD)].</ref>. The Galileo navigation data (e.g. satellite ephemeris) is referenced to the GTRF. Accordingly, the user position coordinates derived from Galileo position solutions are referenced to GTRF.

Galileo GTRF is the independent and highly accurate realisation of the international Terrestrial Reference System based on the estimated coordinates of each one of the Galileo Sensor Station (GSS) sites. The Geodetic Reference Service Provider (GRSP) entity supports the Galileo Control Centre in realising the Galileo Terrestrial Reference Frame (GTRF).

At any time, the alignment between the GTRF and the latest physical realisation of the ITRF is such that the difference between the ITRF and the GTRF coordinates of the ITRF stations/markers used in the realisation of the GTRF is less than 3 cm (2σ). The GTRF is regularly aligned if new ITRF realisations are published. , Galileo OS user equipment needs to apply the appropriate valid transformation parameters between the latest ITRF and the desired reference frame.

== BeiDou Coordinate System (BDC) ==

The BeiDou Coordinate System (BDC) used to compute BeiDou navigation data is consistent with China Terrestrial Reference Frame (CGCS) 2000, which in turn is referred to ITRF97 with the epoch of 2000.0.

The main parameters of the reference ellipsoid are nearly the same as those defined by ITRS with the semi major axis (a), second degree harmonic coefficient (J2), and the mean angular velocity of the Earth (ω) the same as those of the ellipsoid of GRS1980. The gravitational mass (GM) constant adopts the value of WGS-84 (Wei, 2003). The flattening of the ellipsoid of BDC is f = 1/298.257222101<ref>[https://www.nap.edu/read/13292/chapter/10 Global Navigation Satellite Systems: Report of a Joint Workshop of the National Academy of Engineering and the Chinese Academy of Engineering (2012)]</ref>.

Please find below the geodetic constants and parameters of Earth Ellipsoid CGCS2000:

::::[[File:BeiDou.png|none|thumb|540px]]

==Notes==
<references group="footnotes"/>

==Credits==
This article was initially written by Technical University of Catalonia, Spain and updated by GMV to introduce the Beidou Reference Frame information according to the references.

==References==
<references/>

[[Category:GNSS Time Reference, Coordinate Frames and Orbits]]
[[Category:GPS Reference Systems]]
[[Category:GALILEO Reference Systems]]

Galileo Receivers

2026-04-16T14:27:29Z

Gema.Cueto: Updated reference ICD/SDD links

{{Article Infobox2
|Category=GALILEO
|Editors=GMV
|Level=Intermediate
|YearOfPublication=2011
|Logo=GMV
|Title={{PAGENAME}}
}}
The [[GALILEO General Introduction|Galileo]] System is an independent, global, European-controlled, satellite-based navigation system and provides a number of services to users equipped with Galileo-compatible receivers.

Basic elements of a generic [[GNSS Receivers General Introduction|GNSS Receiver]] are an antenna with pre-amplification, an L-band radio frequency section, a microprocessor, an intermediate-precision oscillator, a feeding source, some memory for data storage, and an interface with the user. The calculated position is referred to the antenna phase centre.

==Galileo receivers==
[[File:ArchitectureGalileoReceiver.PNG|450px|A Galileo Acquisition Receiver Architecture|right|thumb]]
The Galileo global navigation satellite system employs many new methods and technologies to offer superior performance and reliability. Development of the advanced receivers required to make use of the system is continuing.<ref name="EsaGalileoweb">[http://www.esa.int/esaNA/SEMY800DU8E_galileo_0.html ESA Galileo web page]</ref>

A GALILEO Receiver is a device capable of determining a navigation solution by processing the signal broadcasted by Galileo satellites. Once the signal is acquired and tracked, the receiver application decodes the navigation message. The navigation data contain all the parameters that enable the user to perform positioning service. Data needed to perform positioning:<ref name="OS-SDD">[https://www.gsc-europa.eu/sites/default/files/sites/all/files/Galileo-OS-SDD_in_force.pdf Galileo Open Service - Service Definition Document]</ref>
# Ephemeris which are needed to compute the position of the satellite to the user receiver.
# Time and clock correction parameters which are needed to compute satellite clock offsets and time conversions.
# Service parameters with satellite health.
# The ionospheric parameters model, needed for single-frequency users.
# Almanac which allow less precise computation of the position of all the satellites in the constellation to facilitate the initial acquisition of the signals by the receiver.

For single frequency receivers, the Broadcast Group Delays are also needed.

Up-to-date ephemeris are needed to indicate the position of the satellite to the user receiver. Time and clock correction parameters for all the satellites are needed to compute pseudo-range. Receivers must retrieve the values of navigation parameters relevant to the type of navigation solution to be computed from the most recent navigation data set broadcast on a Healthy SIS by the Galileo system after the start of the current receiver operation. The navigation performance can be increased by implementing fault detection and isolation algorithms, as those based on the consistency of redundant pseudorange data sets (such as Receiver Autonomous Integrity Monitoring algorithms)<ref name="OS-SDD"/>.

==Particularities==
Each GNSS system uses a specific [[Reference Frames in GNSS| Reference Frame]]; although a multi-constellation receiver is able to convert all information to the same common frame, a Galileo-only receiver uses the Galileo GTRF reference frame.
In an analogous way, each system has its own [[Time References in GNSS| time reference]] defined by the respective control segments; the time reference for Galileo is called “Galileo System Time” (GST).

Each GNSS System transmits its own navigation message, defined in the respective Signal In Space Interface Control Documents, SIS ICD<ref name="SIS_ICD">[https://www.gsc-europa.eu/sites/default/files/sites/all/files/Galileo_OS_SIS_ICD_in_force.pdf Applicable Galileo Open Service – SIS ICD]</ref>. As an example, the satellites transmit information that allows the receiver to compute their positions. For the case of Galileo (in-line with GPS but unlike GLONASS), the satellites transmit the orbit parameters as updated by the Ground Segment and refreshed every 3 hours (in nominal operations). The Galileo receiver then [[GPS and Galileo Satellite Coordinates Computation| computes the satellite position]] based on these transmitted ephemeris parameters.

Another distinction regarding the transmitted navigation message with impact on the receiver is the ionospheric parameters transmitted to support the single frequency receiver in computing the ionospheric error; Galileo uses the [[NeQuick Ionospheric Model]].

GNSS signals modulation, structure, navigation message contents and formats are often different among signals from the same system and from different systems. Most of these characteristics are easily implemented at the receiver (e.g. requiring only “software modifications”, such as the use of different PRN codes or the ability to cope with different message structures). The main difference among GNSS receivers falls into the specific characteristics that have impact at RF level, such as the [[CDMA FDMA Techniques| Multiple Access Techniques]] employed. Galileo (as GPS and BeiDou) uses CDMA techniques allowing a simpler RF module (than for example GLONASS), since all signals in the same frequency band have a common carrier.

It should be noted that the current trend consists on facilitating the access of each system to the receivers, i.e. fomenting multi-constellation receivers. Hence, most discussions and agreements among the systems’ responsible are conducted in the sense of taking this effort out of the user segment, focusing on [[Principles of Compatibility among GNSS| compatibility]] and [[Principles of Interoperability among GNSS| interoperability]] aspects in the system design.

==Galileo receiver chain==
Galileo sensor stations are equipped with high-performance, ultra-reliable receivers. The stations provide measurement data to the Galileo system central processing facilities for establishing system integrity and performing satellite orbit determination and time synchronisation.

==Receivers==

GNSS Receivers manufacturers have already made multi-constellation receivers designed for a variety of [[GNSS Applications|applications]]. These receivers support a wide range of satellite signals, including Galileo signals in E1 and E5 bands. Examples for devices that implement Galileo and user receiver technology trends can be found on the GSA website and in relevant GSA publications such as Market<ref name="GSA-Market">[https://www.gsa.europa.eu/market/gnss-market GSA Market website]</ref> and User Technology reports<ref name="GSA-User-Tech">[https://www.gsa.europa.eu/european-gnss/gnss-market/gnss-user-technology-report GSA User Technology Report]</ref> respectively.

The Open Service Interface Control Document (ICD) for Galileo is available<ref name="SIS_ICD"></ref>, so receiver manufacturers can already work to prepare the acquisition of real Galileo data.
Furthermore, the European GNSS Agency (GSA) has been supporting a number of activities within the user segment<ref>[https://www.gsa.europa.eu/ European GNSS Agency (GSA)]</ref>.

==References==
<references/>

[[Category:GALILEO]]
[[Category:GALILEO Receivers]]

Galileo Performances

2026-04-16T14:20:59Z

Gema.Cueto: Updated reference ICD/SDD links

{{Article Infobox2
|Category=GALILEO
|Editors=GMV
|Level=Basic
|YearOfPublication=2011
|Logo=GMV
|Title={{PAGENAME}}
}}
Galileo system is a space-based global navigation satellite system (GNSS) that provides reliable positioning, navigation, and timing services to users on a continuous worldwide basis.
The Galileo system, once fully operational, will offer four high-performance [[Galileo Services|services]] worldwide:
* [[Galileo Open Service (OS)|Open Service (OS)]]: Galileo open and free of charge service set up for positioning and timing services.
* [[Galileo Commercial Service (CS)|High Accuracy Service (HAS)]]: A service complementing the OS by providing an additional navigation signal and added-value services in a different frequency band. The HAS signal can be encrypted in order to control the access to the Galileo HAS services.
* [[Galileo Public Regulated Service (PRS)|Public Regulated Service (PRS)]]: Service restricted to government-authorised users, for sensitive applications that require a high level of service continuity.
* [[Galileo Search and Rescue Service|Search and Rescue Service (SAR)]]: Europe´s contribution to COMPAS-SARSAT, an international satellite-based search and rescue distress alert detection system.

The Galileo [[GNSS Performances|performances]] are different for each service. For the [[GALILEO Open Service|Galileo Open Service (OS)]] no specific requirements of [[Integrity|integrity]] are applicable. The expected [[GNSS Performances|performances]], once Galileo system is fully deployed, for horizontal positioning [[Accuracy|accuracy]] at 95% for a dual-frequency receiver are 4 m (8 m for vertical [[Accuracy|accuracy]]), with an [[Availability|availability]] of the service of 99.5% <ref name="Galileo OS SDD">[https://www.gsc-europa.eu/sites/default/files/sites/all/files/Galileo-OS-SDD_in_force.pdf Galileo Open Service Service Definition Document]</ref>.

In the case of the [[GALILEO Public Regulated Service|Galileo Public Regulated Service (PRS)]], the [[Availability|availability]] of the service should be 99.5% <ref name="GALHLD"> Galileo Mission High Level Definition, v7.1.</ref>.

== Galileo Service Level Perfomances==
The performances requirements for each service are the following:

===Galileo Open Service Performances===

The expected performance once full deployment of the Galileo system at FOC are<ref name="Galileo OS SDD">[https://www.gsc-europa.eu/sites/default/files/sites/all/files/Galileo-OS-SDD_in_force.pdf Galileo Open Service Service Definition Document]</ref>:

{| class="wikitable" align="center"
|+align="bottom" |''Service Performances for [[Galileo Open Service (OS)|Galileo Open Service]]''
|-
! rowspan="2" |
! colspan="2"| Galileo Open Service (positioning & timing)
|- align="center"
! Single Frequency (SF)
! Dual Frequency (DF)
|- align="center"
! Coverage
| colspan="2"| Global
|- align="center"
! rowspan="2" | Accuracy (95%)
| Horizontal: 15 m
| Horizontal: 4m
|- align="center"
| Vertical: 35 m
| Vertical: 8m
|- align="center"
! Availability
| colspan="2"| 99.5 %
|- align="center"
! Timing Accuracy wrt UTC/TAI
| colspan="2" | 30 ns
|- align="center"
! Ionospheric Correction
| Based on SF Model
| Based on DF Measurements
|- align="center"
! Integrity
| colspan="2"| No
|}

Galileo declared its Initial Services status in December 2016 as the first step towards full operational capability. Galileo system deployment will continue with additional satellite launches to enlarge the constellation until it is completed, reaching the Full Operational Capability (FOC) of the Galileo system.
Galileo OS SDD defined a series of Minimum Performance Levels to be achieved until FOC is reached <ref name="Galileo OS SDD">[https://www.gsc-europa.eu/sites/default/files/sites/all/files/Galileo-OS-SDD_in_force.pdf Galileo Open Service Service Definition Document]</ref>:

{| class="wikitable" align="center"
|+align="bottom" |''Minimum Performance Levels for Galileo Open Service Initial Services''
! colspan="2" |
! rowspan="1" | Galileo Open Service Initial Services
|- align="center"
! rowspan="2" | SIS Ranging
| Accuracy (95%)
|2m
|- align="center"
| Availability
|87%
|- align="center"
! rowspan="5" | Timing
| UTC Time Dissemination Accuracy(95%)
| 30 ns
|- align="center"
| UTC Frequency Dissemination Accuracy (95%)
| 3E-13
|- align="center"
| GGTO Determination Accuracy (95%)
| 20 ns
|- align="center"
| UTC Availability
| 87%
|- align="center"
| GGTO Availability
| 80%
|}

Galileo Performance Reports against these MPL values are published in GSC website <ref name="Performance stadistics">[https://www.gsc-europa.eu/electronic-library/performance-reports Galileo Performance Reports in GSC website]</ref>.

===Galileo High Accuracy Service===

The [[Galileo Commercial Service (CS)|Galileo High Accuracy Service]] complements the OS by providing an additional navigation signal and added-value services in a different frequency band. The HAS signal can be encrypted in order to control the access to the Galileo HAS services. Receiver positioning accuracy is foreseen to be at decimetre level.

The Galileo HAS comprises two services levels<ref name="HAS_note">[https://www.gsc-europa.eu/sites/default/files/sites/all/files/Galileo_HAS_Info_Note.pdf Galileo High Accuracy Service, Info Note]</ref>:
*Service Level 1 (SL1) with global coverage; providing high accuracy corrections (orbits, clocks) and biases (code and phase) for Galileo E1/E5b/E5a/E6 and E5AltBOC and GPS L1/L5/L2 signals.
*Service Level 2 (SL2): with regional coverage; providing SL1 corrections plus atmospheric (at least ionospheric) corrections and potential additional biases.

Next table summarizes the performances for each of the Galileo HAS Service levels:

{| class="wikitable" align="center"
|+align="bottom" |''Table 1- Main HAS target performances<ref name="HAS_note"/>''
|-
! PARAMETER
! Service Level 1
! Service Level 2
|- align="center"
| Coverage
| Global
| European Coverage Area (ECA)
|- align="center"
| Horizontal Accuracy 95%
| < 20cm
| < 20 cm
|- align="center"
| Vertical Accuracy 95%
| < 40cm
| < 40 cm
|- align="center"
| Convergence Time
| < 300 s
| < 100 s
|- align="center"
| Availability
| 99%
| 99%
|}

===Galileo Public Regulated Service Performances===
The expected performances of the Galileo PRS service are<ref name="GALHLD"> Galileo Mission High Level Definition, v7.1.</ref>:

{| class="wikitable" align="center"
|+align="bottom" |''Service Performances for [[Galileo Public Regulated Service (PRS)|Galileo PRS]] ''
|-
! rowspan="2" |
! rowspan="1"| Galileo Public Regulated Service (PRS)
|- align="center"
! Dual Frequency (DF)
|- align="center"
! rowspan="2" | Accuracy (95%)
| Horizontal: 6.5 m
|- align="center"
| Vertical: 12 m
|- align="center"
! Availability
| 99.5 %
|- align="center"
! Timing Accuracy wrt UTC/TAI
| 30 ns
|- align="center"
! Ionospheric Correction
| Based on DF Measurements
|}

===Galileo Search and Recue Service Performances===

Galileo SAR performance values are expressed in terms of Minimum Performance Levels (MPL) for a set of parameters as indicated below<ref name="Galileo SAR SDD">[https://www.gsc-europa.eu/sites/default/files/sites/all/files/SAR-SDD_in_force.pdf Galileo SAR Service Definition Document]</ref>:

{| class="wikitable" align="center"
|+align="bottom" | ''MPL for SAR/Galileo Forward Link Service''
|-
!
!'''Parameter'''
! '''Expected value'''
|-
| rowspan="3" | Service Availability
| Forward Link Service Availability
| > 99%
|-
| European MEOLUT Facility availability in Nominal mode
| > 95%
|-
| European MEOLUT Facility availability in Degraded mode
| > 97.5%
|-
| Detection performance
| Detection probability after 1 transmitted burst
| > 99%
|-
| rowspan ="5" | Location performance
| Location Probability after 1 transmitted burst
| > 90%
|-
| Location Probability after 12 transmitted bursts
| > 98%
|-
| Location Probability after 1 transmitted burst within 5 km
| > 90%
|-
| Location Probability after 12 transmitted bursts within 5 km
| > 95%
|-
| Location Probability after 12 transmitted bursts within 2 km
| > 90%
|}

{| class="wikitable" align="center"
|+align="bottom" | ''MPL for SAR/Galileo Return Link Service''
|-
!'''Parameter'''
! '''Expected value'''
|-
|Return Link Service Availability
| > 95%
|-
| End-to-end Return Link Service Availability
| > 90%
|-
| Galileo System Message Delivery Latency within 15 minutes
| > 99%
|-
| Return Link Message Reception Probability
| > 99%
|-
| End-to-end Message Delivery Loop Latency within 30 minutes
| > 95%
|}

{| class="wikitable" align="center"
|+align="bottom" | ''MPL for SAR/Galileo Space Segment''
|-
!'''Parameter'''
! '''Expected value'''
|-
|SAR Repeater Availability
| > 95%
|}

==Combined services performances==
Galileo is designed to be interoperable with other systems and, therefore, it will, in a great many instances, be used as part of a combined service. The identification of combined services is necessary to:<ref name="GALHLD"/><ref name="Galileo OS SDD">[https://www.gsc-europa.eu/sites/default/files/sites/all/files/Galileo-OS-SDD_in_force.pdf Galileo Open Service Service Definition Document]</ref>

* Meet the most demanding user applications.
* Reduce satellite navigation system weaknesses.
* Provide robust solutions for applications requiring system redundancy for safety and/or security reasons.
* Access future GNSS market.
* Enable and expand new market opportunities.

The most obvious systems to be combined with Galileo are the other existing GNSS systems, GPS,GLONASS, SBAS and GBAS as they share with Galileo many characteristics that facilitate a combination at user level. By combining Galileo with other GNSS systems, improved performance in the following domains can be expected:
* [[Availability]]: Using as an example Galileo in combination with GPS and SBAS systems, the number of operational satellites will be in the region of 60. In normal urban environments this would result in an increased availability for 4 satellites from 40% to more than 90%.
* Position [[Accuracy]]: Allied to an increased availability in restricted environments (urban) is a better geometry of spacecraft or enhanced positioning performance.
* [[Integrity]]: GNSS based integrity systems and techniques, such as [[SBAS General Introduction|SBAS]], [[ARAIM|ARAIM]], [[RAIM|RAIM]] and [[Ground-Based Augmentation System (GBAS)|GBAS]], would benefit from the addition of new constellations, including Galileo, in terms of lower achievable protection levels and/or integrity risk.
* Redundancy: By combining services from separate and fully independent systems full redundancy can be achieved. This is particularly important for Safety of Life applications that require full system backup.

==Notes==
Quarterly Performance Reports are regularly published by the European GNSS Service Centre to provide public information about the measured performance statistics <ref name="Performance stadistics">[https://www.gsc-europa.eu/electronic-library/performance-reports Galileo Performance Reports in GSC website]</ref> for the available Galileo services.

==References==
<references/>

[[Category:GALILEO|Performances]]
[[Category:GALILEO Performance|Performances]]

Galileo Ground Segment

2026-04-16T13:59:43Z

Gema.Cueto: Updated GALILEO OS SDD reference link

{{Article Infobox2
|Category=GALILEO
|Editors=GMV
|Level=Basic
|YearOfPublication=2011
|Logo=GMV
|Title={{PAGENAME}}
}}
The [[GALILEO Ground Segment]] comprises two control centres, a global network of transmitting and receiving stations implementing monitoring and control functions and a series of service facilities which support the provision of the Galileo services.

The core of the [[GALILEO General Introduction|GALILEO ]] ground segment are the two Galileo Control Centres (GCC). Each control centre manages ''control'' functions supported by a Galileo Control Segment (GCS) and ''mission'' functions, supported by a dedicated Galileo Mission Segment (GMS): The GCS handles spacecraft housekeeping and constellation maintenance while the GMS handles navigation system control.<ref name="Galileo System">[https://www.gsc-europa.eu/galileo/system Galileo System at European Galileo Service Centre website ]</ref>

The GCS and GMS interfaces the satellites with a worldwide ground station network implementing control and monitoring functions <ref name="Galileo System">[https://www.gsc-europa.eu/galileo/system Galileo System at European Galileo Service Centre website ]</ref> <ref name="Galileo OS SDD">[https://www.gsc-europa.eu/sites/default/files/sites/all/files/Galileo-OS-SDD_in_force.pdf Galileo Open Service - Service Definition Document ]</ref> :
* '''Galileo Sensor Stations (GSS)''', responsible for collecting and sending in real time the data measurements of Galileo SIS.
* '''Galileo Uplink Stations (ULS)''', responsible for the distribution and uplink of the mission data to the Galileo constellation.
* '''Telemetry, Tracking & Control stations (TT&C)''', responsible for collecting and sending the telemetry data that was generated by the Galileo satellites and also for the distribution and the uplink of the control commands that are necessary to maintain the Galileo satellites and constellation.
The ground segment also comprises a set of Medium-Earth Orbit Local User Terminals (MEOLUTs) serving Galileo’s Search and Rescue service.

[[File:Galileo_Global_Ground_Segment.jpg|left|400px|Galileo Ground Segment|thumb]]

There are several services facilities that complement the core infrastructure <ref name="Galileo System">[https://www.gsc-europa.eu/galileo/system Galileo System at European Galileo Service Centre website ]</ref> <ref name="Galileo OS SDD">[https://www.gsc-europa.eu/sites/default/files/sites/all/files/Galileo-OS-SDD_in_force.pdf Galileo Open Service - Service Definition Document ]</ref><ref name="Galileo SAR SDD">[https://www.gsc-europa.eu/sites/default/files/sites/all/files/Galileo-SAR-SDD.pdf Galileo SAR Service Definition Document ]</ref> :
*The '''European GNSS Service Centre (GSC)''': located in Torrejón (Spain), the centre represents the link between the Galileo Initial OS (and in the future HAS) user communities and the Galileo system
*The '''Geodetic Reference Service Provider (GRSP)''': responsible for the data processing that sustain the Galileo Control Centres in order to realise the Galileo Terrestrial Reference Frame (GTRF) consistently with the International Terrestrial Reference Frame (ITRF)
*The '''Time Service Provider (TSP)''': supports the GCC by realising the Galileo System Time (GST) in order to make it aligned to the Coordinated Universal Time (UTC).
*The '''Galileo Security Monitoring Centre (GSMC)''': located in St. Germain-en-Laye (France) and Madrid (Spain) these facilities are responsible for system security monitoring
*The '''SAR/Galileo Data Service Provider (SGDSP)''': located in Toulouse (France), this entity is responsible of the SAR/Galileo service operations coordination. There is also a MEOLUT Tracking Coordination Facility (MTCF) locate in the SAR/Galileo Service Centre.
*The '''Galileo Reference Centre (GRC)''': located in Noordwijk (The Netherlands), this facility is in charge of the performance monitoring and assessment of Galileo services. This facility is independent from the Galileo core infrastructure and its operations.[[File:Galileo_Ground_Segment_Architecture.png|right|300px|Galileo Ground Segment Architecture|thumb]]

==Galileo Control Segment (GCS)==

The Galileo Control Segment (GCS) is responsible for a large range of functions to support satellite constellation control and management of Galileo satellites. The scope of this functionality includes control and monitoring of the satellites and payload, planning and automation functions that allow safe and correct operations to take place, and the support of payload related operations by means of Telemetry Tracking and Control (TT&C) stations links.
The GCS provides the telemetry, telecommand and control function for the whole Galileo satellite constellation. Its functional elements are deployed within the Galileo Control Centres (GCC) and the six globally distributed Telemetry Tracking and Control (TT&C) stations. To manage this, the GCS uses the TT&C stations to communicate with each satellite on a scheme combining regular, scheduled contacts, long-term test campaigns and contingency contacts.

A hybrid Communication Network interconnects the remote stations (ULS, GSS, and TT&C stations) with the GCC by different means of standard and special radio, wired data and voice communication links, assuring the communication between all the sites. The two Ground Control Centres (GCCs) constitute the core of the Ground Segment. There are two redundant elements located at Fucino (Italy) and Oberpfaffenhofen (Germany).

The TTC Stations include 13-meter antennas operating in the 2 GHz Space Operations frequency bands. During normal operations, spread-spectrum modulation, similar to that used for Tracking and Data Relay Satellite System, [https://www.nasa.gov/directorates/heo/scan/services/networks/tdrs_main TDRSS], and [http://www.esa.int/Our_Activities/Telecommunications_Integrated_Applications/Artemis ARTEMIS] data relay applications, are used, to provide robust, interference free operation. However, when the navigation system of a satellite is not in operation (during launch and early orbit operations or during a contingency) use of the common standard TTC modulation allows non-ESA TTC stations to be used.

==Galileo Mission Segment (GMS)==
[[File:GMS_Fucino.JPG|300px|left|thumb]]

The Galileo Mission Segment (GMS) consists of facilities deployed in the two Galileo Control Centres (GCCs) plus a series of Mission Up-Link Stations (ULS) and Galileo Sensor Stations (GSS) deployed at remote sites located around the world.
The GMS is responsible for the determination and uplink of navigation data messages needed to provide the navigation and timing data. For this purpose, it uses a global network of Galileo Sensor Stations (GSS) <ref name="Galileo System">[https://www.gsc-europa.eu/galileo/system Galileo System at European Galileo Service Centre website ]</ref> to monitor the navigation signals of all satellites on a continuous basis, through a comprehensive communications network using commercial satellites as well as cable connections in which each link is duplicated for redundancy.

The GMS communicates with the Galileo satellites through a global network of Mission Up-Link Stations (ULS), installed at five sites, each of which hosts a number of 3-meter antennas. ULSs operate in the 5 GHz Radionavigation Satellite (Earth-to-space) band.

The GMS uses the GSS network in two independent ways. The first is the Orbitography Determination and Time Synchronisation (OD&TS) function, which provides batch processing every ten minutes of all the observations of all satellites over an extended period and calculates the precise orbit and clock offset of each satellite, including a forecast of predicted variations (SISA - Signal-in-Space Accuracy) valid for the next hours. The results of these computations for each satellite are up-loaded into that satellite nominally every 100 minutes using a scheduled contact via a Mission Up-link Station.

The OD&TS operation thus monitors the long-term parameters due to gravitational, thermal, ageing and other degradations.

==Control Centres Components==

The Galileo Control Centres include components of the two Galileo segments, GCS and GMS.

The main GMS facilities are the following ones:
*OSPF: Orbit determination and Synchronization Processing Facility, in charge of the determination of satellite navigation parameters, i.e., ephemeris computation, satellite clock prediction, and determination of the Signal-in-Space accuracy (SISA).
*MGF: Message Generation Facility, which is the facility needed to multiplex all the messages either generated within the GCC or received by external entities, into a single data stream to be sent to each ULS in order to be uploaded to spacecrafts.
*PTF: Precision Timing Facility, responsible for the generation of a physical realization of Galileo System Time (GST) which is provided to all elements for time synchronization purposes.
*GACF: Ground Assets Control Facility, monitoring and controlling all the elements of the GMS in real time.
*MUCF: Mission Uplink Control Facility, which is responsible for the on-line and off-line mission monitoring and control including the Galileo overall long-, mid- and short-term mission planning and uplink scheduling.
*MSF: Mission Support Facility, used to the off-line support functions including the computation of configuration and calibration data for the real-time elements.
*MTPF: Maintenance and Training Platform, which contains the instances of all elements and support equipment for maintenance and training purposes.
*GMS KMF: GMS Key Management Facility, that supports security aspects and data protection (generation of encryption keys, encryption/decryption process,...).
*SPF: Service Product Facility, which is dedicated to the implementation of the exchange gateway between the GCC and the external world.

The main GCS facilities are:
*SCCF: Spacecraft & Constellation Control Facility, that performs the on-line monitoring and control of the satellites, both for routine and critical operations.
*SCPF: Spacecraft & Constellation Planning Facility, which handles the problem of scheduling regular contact (once per orbit) with all satellites in the constellation to support routine operations and special extended contacts to support critical operations.
*FDF: Flight Dynamics Facility, responsible for non-nominal orbit determination (GMS provides nominal) and manoeuver planning.
*OPF: Operations Preparation Facility, responsible for preparation and configuration control of all operational databases and procedures, including those that are destined for automated execution.
*CMCF: Central Monitoring & Control Facility, that supports the monitoring and control of all GCS ground assets, including the TT&C stations, GCC resident facilities and networks.
*GCS KMF: GCS Key Management Facility, that supports security aspects and data protection (generation of encryption keys, encryption/decryption process...).
*CSIM: Constellation Simulator, which is used for validation of operational process, training and anomalies investigation.

==Credits==
Edited by GMV, using information from the Galileo - Open Service – Service Definition Document and the European GNSS Service Centre website as indicated through the references.
<references group="footnotes"/>
==References==
<references/>

[[Category:GALILEO]]
[[Category:GALILEO Architecture]]
[[Category:GALILEO Ground Segment]]

Galileo Architecture

2026-04-16T13:50:55Z

Gema.Cueto: Fixed GALILEO OS SDD reference link

The [[GALILEO General Introduction|Galileo]] System is an independent, global, European-controlled, satellite-based navigation system and will provide a number of guaranteed services to users equipped with Galileo-compatible receivers once it achieves its Full Operational Capability foreseen for 2020. From 2016, Galileo moved from a testing phase to the provision of life services thanks to the Galileo Initial Services declaration.

To ensure GALILEO services, a specific architecture is deployed, that consists of 30 satellites, to be deployed in a staggered approach, and the associated ground infrastructure.<ref name="Galileo-OS-SDD">[https://www.gsc-europa.eu/sites/default/files/sites/all/files/Galileo-OS-SDD_in_force.pdf Galileo Open Service - Service Definition Document]</ref> The Galileo system is divided into three major segments: [[GALILEO Space Segment|Space Segment]], [[GALILEO Ground Segment|Ground Segment]] and [[GALILEO User Segment|User Segment]].

==Introduction==
[[File:GalileoFOCArchitecture.JPG|300px|Galileo Architecture|thumb]]

The Galileo infrastructure is composed of:
* a constellation of 30 satellites (including 6 spares) in Medium-Earth Orbit (MEO). Each satellite contains a navigation payload and a search and rescue transponder;
* a global network of Galileo Sensor Stations (GSS) providing coverage for clock synchronisation and orbit measurements;
* two Control Centres;
* a network of Mission Uplink stations;
* Telemetry, Tracking and Control (TT&C) stations.
* additional core infrastructure to service which support the provision of the Galileo service.

This infrastructure is organized in two segments, the [[GALILEO Space Segment|Space Segment]] and the [[GALILEO Ground Segment|Ground Segment]], to be complemented by the user receivers, which compose the [[GALILEO User Segment|User Segment]].

==GALILEO Space Segment==
[[File:Galileo Space Segment.jpg|250px|Galileo Space Segment|left|thumb]]
The main functions of the [[GALILEO Space Segment|Galileo Space Segment]] are to generate and transmit code and carrier phase signals with a specific [[GALILEO Signal Plan|Galileo signal structure]], and to store and retransmit the navigation message sent by the [[GALILEO Ground Segment|Control Segment]]. These transmissions are controlled by highly stable atomic clocks on board the satellites.

When Galileo is fully operational, there will be 30 satellites in Medium Earth Orbit (MEO) at an altitude of 23,222 kilometres. The satellites will occupy each of three orbital planes inclined at an angle of 56° with respect to the equator. The satellites will be spread evenly around each plane and will take about 14 hours to orbit the Earth. Each orbital plane includes 8 satellites uniformly distributed within the plane. The angular shift between satellites in two adjacent planes is 15º.
One satellite in each plane will be a spare, on stand-by should any operational satellite fail. The full constellation includes 6 spare satellites, resulting a walker 24/3/1 constellation. These spare satellites can be activated and allocated to a given operational slot depending on maintenance or service evolution activities.
The constellation geometry repetition period corresponding to the nominal orbital parameters is 10 days (corresponding to 17 orbital revolutions). This means that for any fixed Galileo user, the local satellite geometry at a given instant is repeated every 10 sideral days.
In the following table are shown the Nominal Value of the different Reference Orbit Parameters:

{| class="wikitable" align="center"
|+align="bottom" |''Galileo Reference Orbit Parameters''
|-
! Reference Orbit Parameter
! Nominal Value
|- align="center"
| Orbit semi-major axis, m
| 29599801
|- align="center"
| Orbit eccentricity
| 1E-07
|- align="center"
| Orbit inclination, deg
| 56.0
|- align="center"
| Argument of Perigee, deg
| 0.0
|- align="center"
|}

Highly accurate atomic clocks are installed on these satellites. Each of the 30 satellites in the Galileo system has two of each type of clock on board, a rubidium and a hydrogen maser clock. The frequency is at around 6 GHz for the rubidium clock and at around 1.4 GHz for the hydrogen clock. The Galileo system uses the clock frequency as a very stable reference by which other units can generate the accurate signals that the Galileo satellites will broadcast. The broadcast signals also provide a reference by which the less stable user receiver clocks can continuously reset their time.

The satellites are deployed gradually according to the [[GALILEO_Future_and_Evolutions|Galileo Program schedule]].

==GALILEO Ground Segment==
The [[GALILEO Ground Segment|Galileo Ground Segment]] is the responsible for the proper operation of the GNSS system. It comprises two control centres, a global network of transmitting and receiving stations implementing monitoring and control functions and a series of service facilities which support the provision of the Galileo services<ref name="Galileo-OS-SDD"></ref>.

The core of the GALILEO ground segment are the two Galileo Control Centres (GCC). Each control centre manages ''control'' functions supported by a '''Galileo Control Segment (GCS)''' and ''mission'' functions, supported by a dedicated '''Galileo Mission Segment (GMS)'''. The GCS handles spacecraft housekeeping and constellation maintenance while the GMS handles navigation system control. The GCS and GMS interfaces the satellites with a worldwide ground station network implementing control and monitoring functions<ref name="Galileo-OS-SDD"/><ref name="Galileo_System">[https://www.gsc-europa.eu/galileo/system Galileo System at European Galileo Service Centre website]</ref>.

The '''Galileo Control Segment (GCS)''' is responsible for a large range of functions to support satellite constellation control and management of Galileo satellites. The scope of this functionality includes control and monitoring of the satellites and payload, planning and automation functions that allow safe and correct operations to take place, and the support of payload related operations by means of Telemetry Tracking and Control (TT&C) stations links. The GCS provides the telemetry, telecommand and control function for the whole Galileo satellite constellation. Its functional elements are deployed within the Galileo Control Centres (GCC) and the six globally distributed Telemetry Tracking and Control (TT&C) stations. To manage this, the GCS uses the TT&C stations to communicate with each satellite on a scheme combining regular, scheduled contacts, long-term test campaigns and contingency contacts.

The '''Galileo Mission Segment (GMS)''' consists of facilities deployed in the two Galileo Control Centres (GCCs) plus a series of Mission Up-Link Stations (ULS) and Galileo Sensor Stations (GSS) deployed at remote sites located around the world. The GMS is responsible for the determination and uplink of navigation data messages needed to provide the navigation and timing data. For this purpose, it uses a global network of Galileo Sensor Stations (GSS)<ref name="Galileo-OS-SDD"/><ref name="Galileo_System"/> to monitor the navigation signals of all satellites on a continuous basis, through a comprehensive communications network using commercial satellites as well as cable connections in which each link is duplicated for redundancy.

==GALILEO User Segment==
The [[GALILEO User Segment|Galileo User Segment]] is composed by [[GALILEO Receivers|Galileo receivers]]. Their main function is to receive Galileo signals, determine pseudoranges (and other observables), and solve the navigation equations in order to obtain their coordinates and provide a very accurate time.

==Notes==
<references group="footnotes"/>
==References==
<references/>{{Article Infobox2
|Category=GALILEO
|Editors=GMV
|Level=Basic
|YearOfPublication=2011
|Logo=GMV
|Title={{PAGENAME}}
}}

[[Category:GALILEO|Architecture]]
[[Category:GALILEO Architecture]]
[[Category:GALILEO Ground Segment]]

Galileo Future and Evolutions

2026-04-16T12:56:25Z

Gema.Cueto: Fixed broken links

{{Article Infobox2
|Category=GALILEO
|Editors=GMV
|Level=Basic
|YearOfPublication=2011
|Logo=GMV
|Title={{PAGENAME}}
}}
The Galileo program is Europe's initiative for a state-of-the-art global satellite navigation system, providing a highly accurate, guaranteed global positioning service under civilian control.<ref name="CR Galileo">Council Resolution of 19 July 1999 on the involvement of Europe in a new generation of satellite navigation services -Galileo- Definition phase [http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:C:1999:221:0001:0003:EN:PDF (1999/C 221/01)]</ref> While providing autonomous navigation and positioning services, the system established under the Galileo program is at the same time interoperable with other GNSS systems (such as [[GPS General Introduction|GPS]], [[GLONASS General Introduction|GLONASS]] or [[BeiDou General Introduction|BEIDOU]]). The system, once fully deployed, will consist of 31 satellites, to be deployed in a staggered approach, and the associated ground infrastructure.<ref>[http://www.esa.int/esaNA/galileo.html ESA Galileo web page]</ref>

==Galileo phases==
The Galileo program has been structured according to three main phases:<ref name="EC GAL web">[https://defence-industry-space.ec.europa.eu/eu-space/galileo-satellite-navigation_en European Commision Galileo website]</ref><ref name="Mid-term review">[http://europa.eu/rapid/press-release_MEMO-11-26_en.htm Mid-term review of the European satellite radio navigation programmes]</ref>
# In-Orbit Validation (IOV) phase:
#:The IOV phase consisted of qualifying the system through tests and the operation of two experimental satellites and a reduced constellation of four operational satellites and their related ground infrastructure.
#:The two experimental satellites were launched in respectively December 2005 and April 2008. Their purpose was to characterize the Medium-Earth Orbit (MEO) environment (radiations, magnetic field etc) and to test in such environment the performance of critical payload technology (atomic clocks and radiation hardened digital technology). They also provided an early experimental signal-in-space allowing securing the frequency spectrum required for Galileo in accordance with WRC RNSS allocations. The first 2 Galileo operational satellites were launched by ESA with the Soyuz VS01 flight on 21st October 2011 and were declared fully operational since April 2012. The next two Galileo satellites, completing the IOV quartet, were launched on 12th October 2012 by the Soyuz ST-B launcher from the Guiana Space Centre (please refer to [http://www.esa.int ESA website] for videos on the launches) and they are transmitting signals on E1, E5 and E6 band since December 2012. More information on the Galileo IOV Satellites can be found [[Galileo_IOV_Satellites|here]]. The [http://www.esa.int/Our_Activities/Navigation/Galileo_fixes_Europe_s_position_in_history first position fix] using the IOV satellite quartet, was reported on the 12th of March 2013 by ESA's navigation laboratory in the Netherlands. After that ESA started a wide variety of IOV tests all across Europe to assess the performance of the system sub-set already deployed. As of February 2014 Galileo achieved In-Orbit Validation since the results of the tests shown that "Galileo works, and it works well". The performance to be achieved will effectively be reached as more satellites are launched and ground stations come on line.<ref>[http://gpsworld.com/galileo-achieves-in-orbit-validation/ Galileo Achieves In-Orbit Validation], GPS World, GPS World Staff, February 2014</ref><ref>[http://www.esa.int/Our_Activities/Navigation/Galileo_works_and_works_well Galileo Works, And Works Well], ESA, February 2014</ref>
# Initial Operational Capability (IOC) phase:
#:The IOC stage represents the partial commissioning of the ground and space infrastructure as from 2014-2015 and the provision of the [[GALILEO Open Service|Open Service]], the [[GALILEO Search and Rescue Service|Search And Rescue service]] and the [[GALILEO Public Regulated Service|PRS]].The provision of these Galileo Initial Services was declared in December 2016.<ref name ="goes live">[http://europa.eu/rapid/press-release_IP-16-4366_en.htm Galileo goes live!]</ref> The procurement of the IOC phase included the first batch of satellites (14 additional satellites to the 4 IOV satellites), the launch services, the needed mission and control ground infrastructure, the system support services and the corresponding operations<ref>Commission awards major contracts to make Galileo operational early 2014, [http://europa.eu/rapid/pressReleasesAction.do?reference=IP/10/7 IP/10/7], Brussels, 7 January 2010.</ref>. Details on the different steps of this phase are presented in [[#Galileo Deployment | Galileo Deployment]]
# Full Operational Capability (FOC) phase:
#:The FOC phase consists of the deployment of the full system which will consist of 30 satellites, control centres located in Europe and a network of sensor stations and uplink stations installed around the globe. Galileo's Full Operational Capability (FOC) is expected for 2020, in a staggered approach from the IOC phase. Four new Galileo satellites were put on orbit on top of an Ariane 5, on July 25, 2018 from the European spaceport in Kourou, French Guiana. This launch brings the Galileo constellation finalization, with all objectives achieved: Galileo signal is better than expected and now usable in all new mobile phones.

The list of past and present satellites of the Galileo navigation system, as well as the following satellite launches, can be consulted in<ref name="Galileo FOC">[https://en.wikipedia.org/wiki/List_of_Galileo_satellites Galileo FOC]</ref>

The definition phase and the development and In-Orbit Validation phase of the Galileo program was carried out by the [http://www.esa.int/ European Space Agency (ESA)] and co-funded by ESA and the [http://europa.eu/ European Union]. The Full Operational Capability phase of the Galileo program is fully funded by the European Union and managed by the [https://defence-industry-space.ec.europa.eu/eu-space/galileo-satellite-navigation_en European Commission]. The Commission and ESA signed a delegation agreement by which ESA acts as design and procurement agent on behalf of the Commission.

== Galileo Deployment ==

Galileo’s seventh and eighth satellites launched successfully in March 2015. The European Space Agency (ESA) planned four more satellites to reach orbit in that year, and space maneuvers for Galileo 5 and 6 were completed, with a recovery plan currently under study.
Both satellites 7 and 8 started transmitting signals in May 2015, with the first E1 and E5 signals from Galileo 8 received on May 21 and the first E1 and E5 signals from Galileo 7 on May 25.<ref>[http://gpsworld.com/newest-galileo-satellites-now-transmitting/ Both New Galileo Satellites Now Transmitting]</ref> 
A further two Galileo satellites were successfully launched on September 11, 2015, raising the total number of satellites in the constellation to 10. <ref>[http://insidegnss.com/esa-launches-two-galileo-satellites/ ESA Launches Two Galileo Satellites]</ref>
Several stations participating in the International GNSS Service Multi-GNSS Experiment started tracking the new satellites on October 12th, 2015. <ref>[http://gpsworld.com/newest-gnss-satellites-being-tracked/ Newest GNSS Satellites Being Tracked]</ref> 
The 11th and 12th Galileo satellites were launched on December 17, 2015 <ref>[http://insidegnss.com/galileo-program-adds-pair-of-satellites-to-constellation/ Galileo Program Adds Pair of Satellites to Constellation]</ref> and became operational in the end of April 2016 <ref>[http://insidegnss.com/two-more-galileo-satellites-set-healthy/ Two More Galileo Satellites Set Healthy]</ref>. 
The total number of satellites in the constellation was increased to 14 on May 24, 2016, with the launch of two additional satellites from the French Guiana <ref>[http://insidegnss.com/successful-launch-continues-build-out-of-galileo-constellation/ Successful Launch Continues Build-Out of Galileo Constellation]</ref>

On November 17th, 2016, the Galileo constellation was reinforced with another 4 satellites. <ref>[http://gpsworld.com/the-launch-of-4-and-declaration-of-galileo-operations/ The launch of 4 and declaration of Galileo operations]</ref>

With this last launch, Galileo became operational for initial services on December 15th, 2016. <ref name ="goes live">[http://europa.eu/rapid/press-release_IP-16-4366_en.htm Galileo goes live!]</ref>. Four new Galileo satellites were successfully launched on December 12th, 2017. This last launch brings the Galileo constellation to a total of 22 satellites.

On April 2017, the Galileo Search And Rescue (SAR) service was officially launched. This new service reduces the detection delay of a distress signal from up to several hours to 10 minutes. The a return link, a signal informing the person in distress that the signal has been received and localized, was declared in January 2020.<ref>[https://www.gsa.europa.eu/newsroom/news/galileo-return-link-service-declared-european-space-conference Galileo Return Link Service declaration]</ref>

[[Galileo Open Service Navigation Message Authentication | Galileo OS-NMA]] capability is gradually being added to Galileo Open Service in the short term. It is a data authentication function for the Galileo Open Service worldwide users, freely accessible to all. OSNMA provides receivers with the assurance that the received Galileo navigation message is coming from the system itself and has not been modified.

OSNMA is authenticating data for geolocation information from the Open Service through the Navigation Message (I/NAV) broadcast on the E1-B signal component. This is realised by transmitting authentication-specific data in previously reserved fields of the E1 I/NAV message. By using these fields, OSNMA does not introduce any overhead to the system, thus the OS navigation performance remains untouched<ref name="OS-NMA">[https://www.gsc-europa.eu/galileo/services/galileo-open-service-navigation-message-authentication-osnma Galileo OS-NMA Roadmap]</ref>.
[[File:OSNMA_Roadmap.png|450px|center|Galileo OSNMA Roadmap|thumb]]
Also, [https://www.euspa.europa.eu/newsroom-events/news/implementation-quasi-pilot-g2g-signals G2G is developing dedicated quasi-pilot signals], for easing the acquisition process at the receiver level, would further support these developments in user technology to reduce the power consumption in the processes of signal acquisition for a faster first fix. This is a real differentiator of Galileo that would significantly reduce the time of acquisition of the Galileo signals, in single and multifrequency scenarios. This is relevant for different Galileo use cases and applications where a requirement at the receiver level is to minimize the energy spent on signal acquisition for the first position fix.

The G2G system and technological development are being supported through ESA's HSNAV GNSS and H2020 Programmes, delegating their technical definition and the management of their activities related to their implementation, guaranteeing compatibility with previous versions, the continuity of Galileo services and their possible integration with Augmentation Systems (SBAS), in the European case, is the EGNOS system, which consists of three additional satellites.

Regarding [[Galileo High Accuracy Service (HAS) | Galileo High Accuracy]], this service will be implemented in a three-step approach<ref name="HAS_note">[https://www.gsc-europa.eu/sites/default/files/sites/all/files/Galileo_HAS_Info_Note.pdf Galileo High Accuracy Service, Info Note]</ref><ref name="HAS_GSC">[https://www.gsc-europa.eu/galileo/services/galileo-high-accuracy-service-has Galileo HAS in GSC website]</ref>:
*Phase 0 (HA testing and experimentation), starting in Q2 2021 focusing on activities aimed at validating Galileo’s dissemination capabilities through the E6B channel and performing initial high-accuracy testing. Internal testing is ongoing since 2019.
*Phase 1 (HA Initial Service) from 2022. Provision of an initial Galileo High Accuracy Service resulting from the implementation of a high-accuracy data generation system processing Galileo system data only. The HA initial service will deliver Service Level 1 only with a reduced performance (below the full service’s targets).
*Phase 2 (HA Full Service). Full provision of the Galileo High Accuracy Service starting from 2023, including Service Level 1 and Service Level 2, fulfilling its target performance (e.g. 20 cm positioning performance).

==Galileo Evolutions==
[[File:Galileo_clock.jpg‎‎|300px|Galileo Clock (artistic interpretation)|thumb]]
The European Parliament and the Council allocated the management of the Galileo programme to the European Commission.<ref>[http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2008:196:0001:0011:en:PDF Regulation (EC) No 683/2008 of the European Parliament and of the Council of 9 July 2008 on the further implementation of the European satellite navigation programmes (EGNOS and Galileo)]</ref>
The European Commission set up a consultative group of GNSS experts called the Mission Evolution Advisory Group (MEAG). MEAG aims at providing EC with independent advice and ''recommendations on potential evolutions of the mission objectives and the service definitions for the European satellite navigation programmes Galileo and EGNOS''.

In April 2013, the member states' Permanent Representatives (Coreper) endorsed the compromise reached between the Council and the European Parliament in their negotiations on a new financial and governance framework for the European satellite navigation systems (EGNOS and Galileo) for the period covered by the multi-annual financial framework for 2014-2020<ref name="EUpress">[http://www.consilium.europa.eu/uedocs/cms_data/docs/pressdata/en/trans/136813.pdf "Council and European Parliament reach agreement on financing and governance of the European satellite navigation systems]</ref>.

The draft regulation contains the following key elements based on a first proposal presented by the Commission in December 2011, excluding the financial envelope<ref name="EUpress"/>:
*A tentative budget of EUR 6.3 billion (at constant 2011 prices), to be fully financed from the EU budget.
*A definition of the EU satellite navigation systems and Programmes and of the services they will provide;
*A new governance framework that establishes a strict division of tasks between the Commission, the European GNSS Agency and the European Space Agency;
*Rules on public procurement, promoting the widest participation possible throughout the Union and ensuring fair competition conditions.

The Galileo Evolutions are currently under technical study within the European GNSS Evolution Programme
(EGEP),<ref name="EGEP">[http://www.esa.int/SPECIALS/GNSS_Evolution/index.html European GNSS Evolution Programme website]</ref> an ESA optional programme supported by 17 Member States and Canada. Its primary aim is to undertake research and development in verification of technologies relating to regional space-based augmentation systems (SBAS) and global navigation satellite systems (GNSS).
Regarding Galileo, EGEP objectives are:
* define future system architectures for Galileo and prepare the technology for future versions of the system;
* provide testbeds and system tools;
* improve Agency knowledge of GNSS performance monitoring and the principal environmental factors influencing performance;
* promote and support scientific exploitation of Galileo.

Another main objective of the EGEP is the preparation of the future generation of Galileo (Galileo Second Generation, G2G), Galileo Second Generation teams are hard at work building twelve satellites that will integrate seamlessly with the current Galileo navigation fleet. With two families of six satellites, developed by Thales Alenia Space (TAS) and Airbus Defence and Space (ADS), the upgraded models will bring countless benefits to users in Europe and around the world. But before they are ready for launch, each satellite must undergo rigorous testing on the ground.

A crucial phase in the development of a new satellite is the System Compatibility Test Campaign (SCTC), a comprehensive round of tests to ensure their full compatibility with ground segment. For the G2 programme, the ground segment is being developed by Thales Alenia Space, GMV, Thales SIX GTS and their industrial partners. The SCTC is divided into multiple phases, with each test case gradually increasing in complexity.<ref name="Galileo 2G">[https://www.esa.int/Applications/Satellite_navigation/Galileo/Galileo_Second_Generation_developing_at_full_speed Galileo Second Generation]</ref>

The Galileo Second Generation (G2G) is expected to deliver improved performance and RNP (Required Navigation Performances) features such as reliability, maintainability, availability, continuity, accuracy and integrity. This is why the European Commission (EC) has decided to launch a Transition Programme with ESA for technical definition and implementation.

The constant need for orbital spare parts to replace end-of-life GALILEO satellites must be taken into account, which will ensure that the European system continues to operate without losing the availability of services. In 2017, twelve additional satellites were requested from the industry to serve as a transition to a future generation, with the objective of maintaining and improving the precision, robustness, availability and integrity performance in its main PNT (Positioning, Navigation and Time) function, as a permanent part of the European and global landscape in the Global Navigation Satellite System (GNSS) and to confer European autonomy over its constellation, for civil use and with governmental applications.

==Notes==
<references group="footnotes"/>
==References==
<references/>

[[Category:GALILEO|Future]]
[[Category:GALILEO Future and Evolutions]]

Principles of Interoperability among GNSS

2026-04-16T11:12:11Z

Gema.Cueto:

{{Article Infobox2
|Category=Fundamentals
|Editors=GMV
|Level=Intermediate
|YearOfPublication=2011
|Logo=GMV
|Title={{PAGENAME}}
}}
Within the last decade, several new (and modernized) global and regional navigation satellite systems have been announced. One of the main technical reasons behind this phenomenon is that a single GNSS system is often not enough to guarantee the target user performances, especially in challenging conditions such as urban environments. Therefore the emergence (and modernization) of GNSS systems entails discussions on [[Principles of Compatibility among GNSS|compatibility]] and interoperability among the different service providers.

==Definition==
Interoperability is defined in the ICG (International Committee on Global Navigation Satellite Systems)<ref name="ICG">[https://www.unoosa.org/oosa/en/ourwork/icg/icg.html International Committe on Glonal Navigation Satellite Systems (ICG) website]</ref> Forum as:

“Interoperability refers to the ability of global and regional navigation satellite systems and augmentations and the services they provide to be used together to provide better capabilities at the user level than would be achieved by relying solely on the open signals of one system”<ref name="Space Sevice Volume">[https://www.unoosa.org/res/oosadoc/data/documents/2018/stspace/stspace75_0_html/st_space_75E.pdf The Interoperable Global Navigation Satellites Systems Space Service Volume”, ed. 2018 (ST/SPACE/75)]</ref>.

In the GNSS context, interoperability should be understood as the capability for user equipment to exploit available navigation signals of different GNSS and to produce a combined solution which generally exhibits performance benefits (e.g. better accuracy, higher availability) with respect to the standalone system solution.

Furthermore, interoperability is often discussed at two different levels: system and signal<ref name="hein">“GNSS Interoperability: Achieving a Global System of Systems or Does Everything Have to Be the Same?”, G. Hein, InsideGNSS, Jan/ Feb 2006. http://insidegnss.com/auto/0106_Working_Papers_IGM.pdf</ref>.

==Interoperability at System Level==

At system level, interoperability can be viewed as the capability of all systems to provide the same solution standalone (with the respective performance constraints). In other words, a GPS, GLONASS or Galileo receiver should be able to provide the same navigation solution – within the respective system accuracy - when used standalone.
In this scope, GPS and Galileo can be said to be interoperable at system level<ref name="hein"></ref>, while bringing the advantage of being independently operated thus providing redundancy to the GNSS user community – hence increasing the market confidence on the technology.

==Interoperability at Signal Level==

Signal interoperability is achieved when the signals provided by different systems are similar enough to allow a GNSS receiver to use those signals with minor modification.
For GNSS, signal interoperability considers the following factors<ref name="hein"></ref>:
*[[Reference Systems and Frames|Reference Frames]]
Although the international civil coordinate reference standard is the International Terrestrial Reference Frame (ITRF), each GNSS has its own reference frame - which depends on the control stations’ coordinates hence guaranteeing independence among systems. Two GNSS are said to be interoperable from a reference frame perspective if the difference between frames is below the target accuracy. As an example, GPS coordinate reference frame is WGS84 whereas Galileo uses Galileo Terrestrial Reference Frame (GTRF); their difference is expected to be within 3 cm, hence guaranteeing interoperability for most applications <ref name=" Galileo OS SDD">[https://www.gsc-europa.eu/sites/default/files/sites/all/files/Galileo-OS-SDD_v1.3.pdf Galileo Open Service SDD]</ref>
*[[Time References|Time Reference]]
Time reference frames refer to the international civilian time standard: Universal Time Coordinated/ Atomic Time (UTC/ TAI). Although GPS Time and Galileo System Time (GST) are expected to be within the nanoseconds order of magnitude, the required parameters to transform the GST time to UTC as part of the Galileo navigation messages. In particular, the Galileo System provides the “Galileo to GPS Time Offset” (GGTO) as part of the navigation messages.. As an alternative, some receivers also isolate this time offset as an additional unknown to be solved within the navigation solution. In solving the set of equations, the time difference is also inherently resolved. The disadvantage of this approach is that at least one additional lie-of-sight measurement is required for solving the set of equations.
*Use of the same carrier frequency
The selection of the same carrier frequency has a high impact on receiver complexity and cost (e.g. it dictates the need for additional band-pass filters). In this scope, Galileo frequency bands have been allocated in the Radio Navigation Satellite Services part of the spectrum. The OS carrier frequencies (in particular E1 and E5a) and their modulation characteristics simplify the combined use of Galileo with other constellations (GPS, GLONASS and BeiDou). GPS and Galileo can be considered interoperable at signal level among themselves in some frequency bands (e.g. L1 and L5/ E5a), but not with the legacy GLONASS signals which use [[CDMA FDMA Techniques|FDMA techniques]], hence a different carrier frequency per satellite. Furthermore, please note that even GPS and Galileo may be considered as not interoperable among themselves in frequency-bands that have no correspondence, such as E5b or L2 – even though still [[Principles of Compatibility among GNSS|compatible]] since no interference is caused on the other system.
*Signals In Space
Aspects of the design of the Signals In Space, such as modulation, signal structure or selection of the codes that require only “software modifications” at the receiver can be considered to not affect interoperability. Furthermore, several working groups have been formed at international level in order to coordinate during the design of the signals design in order to ensure compatibility and signal interoperability. As a consequence, the military GPS-M code and the Galileo Public Regulated Service (PRS) have signal interoperability on L1 band. In addition, QZSS is interoperable with GPS and Galileo both in L1 and E5a/L5 bands.

==International Cooperation==
GNSS signal design (e.g. signal structures, messages, carrier frequencies, codes and modulations) affect directly interoperability and therefore cooperation at international level has been conducted from an early stage of development in order to guarantee interoperability. Several cooperation venues have been undertaken among different parties, either bilaterally or multilaterally. Some examples:
*1998: US-Japan statement on GPS cooperation (QZSS and GPS to be fully compatible and highly interoperable)
*2003: EU-China cooperation agreement leading to regular technical meetings covering interoperability and compatibility between Galileo and BeiDou
*2004: EU-US agreement to provide foundation for cooperation (the result was the creation of four working groups, being the MBOC modulation one of the most striking outcomes at signal level)
*2005 onwards: US-Russia negotiations for an agreement on satellite navigation cooperation. Working groups on compatibility and interoperability have taken place
*2007: US-India joint statement on GNSS cooperation in 2007 – technical meetings have taken place which focused on GPS-IRNSS compatibility and interoperability
*EU has also been in ongoing discussions with India, Russia and Japan. Specific co-operation activities are further listed in [https://www.gsa.europa.eu/galileo/international-co-operation the European GNSS Agency webpage].

At multilateral level, cooperation has been promoted in different contexts, such as:
*ICG (International Committee on Global Navigation Satellite Systems)<ref name="ICG">[https://www.unoosa.org/oosa/en/ourwork/icg/icg.html International Committe on Glonal Navigation Satellite Systems (ICG) website]</ref> that aims at promoting the use of GNSS as well as encouraging compatibility and interoperability among global and regional systems
*APEC (Asia-Pacific Economic Cooperation) GIT (GNSS Implementation Team) focusing on air traffic control and aviation issues

==Receivers==
As a consequence of the emergence (and modernization) of GNSS, GNSS receiver manufacturers claim tend to develop more flexible boards that are able to easily integrate any new system with minor modifications. Currently, there is a wide range of multi-constellation GNSS (including GPS, GLONASS, Galileo and/or BeiDou) and SBAS receivers. Furthermore, many manufacturers are already selling [[GALILEO Receivers|Galileo receivers]] even if the constellation is not yet fully deployed.

Furthermore there are studies showing the advantage of using a modelling language to facilitate the implementation of the navigation message decoding from different GNSS in the receivers, in-line with the respective SIS ICDs<ref>D. Gianni, J. Fuchs, P. De Simone, and M. Lisi, “A Modelling Language to Support the Interoperability of Global Navigation Satellite Systems”, GPS Solutions, Springer Verlag.</ref>.

==Related articles==
*[[GNSS signal]]
*[[CDMA FDMA Techniques]]
*[[Principles of Compatibility among GNSS]]

==References==
<references/>

[[Category:Fundamentals]]
[[Category:GALILEO Interoperability]]
[[Category:GPS Interoperability]]

GLONASS Navigation Message

2026-04-16T11:07:15Z

Gema.Cueto:

{{Article Infobox2
|Category=Fundamentals
|Authors=J. Sanz Subirana, JM. Juan Zornoza and M. Hernandez-Pajares, University of Catalunia, Spain.
|Level=Basic
|YearOfPublication=2011
|Title={{PAGENAME}}
}}
GLONASS satellites modulate two navigation messages at 50 bps onto the standard (C/A) and high accuracy (P) signals, each message providing the users the necessary information for positioning (parameters to compute GLONASS satellites coordinates, their clock offsets, and various other system parameters).

The navigation message of the standard accuracy signal (C/A) is broadcast as continuously repeating superframes with a duration of 2.5 minutes. Each superframe consists of 5 frames of 30 seconds, and each frame consists of 15 strings of 2 seconds duration (100 bits length).

[[File:GLONASS navigation message structure.png|none|thumb|400px|alt=GLONASS navigation message structure|'''''Figure 2:''''' GLONASS navigation message structure (source GLONASS-ICD).]]

The message content divides the data in immediate data of the transmitting satellite and non-immediate data for the other satellites. The immediate data is repeated in the first four strings of every frame. It comprises the ephemeris parameters, satellite clock offsets, satellite healthy flag and the relative difference between carrier frequency of the satellite and its nominal value. The non-immediate data is broadcast in the strings 5 to 15 of each frame (almanac for 24 satellites). The frames I to IV contain almanac for 20 satellites (5 per frame), and the 5th frame almanac for 4 satellites. The last 2 strings of frame 5 are reserved bits (the almanac of each satellite uses 2 strings).

The ephemerides values are predicted from the Ground Control Centre for a 24 hours period, and the satellite transmits a new set of ephemerides every 30 minutes. These data differ from GPS data. Instead of Keplerian orbital elements, they are provided as Earth Centred Earth Fixed (ECEF) Cartesian coordinates in position and velocity, with lunisolar acceleration perturbation parameters. The GLONASS-ICD <ref>[https://glonass-iac.ru/upload/docs/stehos/stehos_en.pdf GLONASS ICD, 2020]</ref> provides the integration equations based on 4th-order-Runge-Kutta method, which includes the second zonal geopotential harmonic coefficient. The almanac is quite similar to the GPS one, given as modified Keplerian parameters, and it is updated approximately once per day.

The navigation message of the high accuracy signal (P) structure is not officially published, but different research groups decoded it. According with these investigations each satellite transmits a superframe, which is composed of 72 frames, each containing 5 strings of 100 bits. A frame needs 10 seconds to be transmitted, thence the total length of message is 12 minutes. The first three frames contain the ephemeris for the transmitting satellite.

==Notes==
<references group="footnotes"/>

==References==
* Hofmann-Wellenhof, B., Lichtenegger, H., K. and Wasle, E., 2008. GNSS - Global Navigation Satellite Systems.. Springer-Verlag, Wien, Austria.
* [http://www.oosa.unvienna.org/pdf/publications/st_space_24E.pdf United Nations, 2004] Report of the action team on global navigation satellite systems (GNSS) – Follow up to the Third United Nations Conference on the Exploration and Peaceful Uses of Outer Space (UNISPACE III).

[[Category:Fundamentals]]
[[Category:GLONASS]]
[[Category:GLONASS Signal Structure]]

Galileo Navigation Message

2026-04-16T11:03:25Z

Gema.Cueto:

{{Article Infobox2
|Category=Fundamentals
|Authors=J. Sanz Subirana, JM. Juan Zornoza and M. Hernandez-Pajares, University of Catalunia, Spain.
|Level=Basic
|YearOfPublication=2011
|Title={{PAGENAME}}
}}
The Galileo satellites broadcast different types of data in four navigation messages: the F/NAV navigation, the I/NAV navigation message, the Commercial Navigation Message (C/NAV) and the Governmental Navigation Message (G/NAV).

The G/NAV navigation message does not belong to the public domain and the C/NAV is not yet defined. Please note that the formerly Commercial Service is now known as High Accuracy Service.

The details of the Galileo Signal Status are provided in the Galileo OS SIS Interface Control Document (ICD). <ref name = "GAL SIS ICD">[https://www.gsc-europa.eu/sites/default/files/sites/all/files/Galileo_OS_SIS_ICD_v2.2.pdf Galileo OS SIS ICD]</ref> No other ICD documents have been published to date.

== General Structure and Contents ==
The Galileo Signal-In-Space data channels transmit different messages type according to the general contents identified in the following table. The F/NAV types of message correspond to the OS and the I/NAV types of messages correspond to both OS and CS (current High Accuracy Service). The following table indicates the signal component associated to each navigation message type. Let us also note that the Return Link Message from Galileo SAR service is provided as part of I/NAV data.

[[File:Message_types.png |none|thumb|400px| Source: Galileo OS SIS ICD <ref name = "GAL SIS ICD">[https://www.gsc-europa.eu/sites/default/files/sites/all/files/Galileo_OS_SIS_ICD_v2.2.pdf Galileo OS SIS ICD]</ref> ]]

The complete navigation message data are transmitted on each data component as a sequence of frames. A frame is composed of several sub-frames, and each sub-frame is composed of several pages. The page is the basic structure for building the navigation message.

All data values encoded using the following bit and byte ordering criteria:
* For numbering, the most significant bit/byte is numbered as bit/byte 0.
* For bit/byte ordering, the most significant bit/byte is transmitted first.

According with the current published ICD <ref name = "GAL SIS ICD">[https://www.gsc-europa.eu/sites/default/files/sites/all/files/Galileo_OS_SIS_ICD_v2.2.pdf Galileo OS SIS ICD]</ref> both F/NAV and I/NAV navigation messages are called super-frame and broadcast as a sequence of frames that are composed of several sub-frames which in turn is composed by several pages.

[[File:Galileo_Navigation_Message_Structure.png |none|thumb|400px]]

The general structure of the navigation messages are common but the number of sub-frames and pages as well as the duration of each page are not the same, as represented in the following table.

{| class="wikitable"
|-
!|Message||Channel||Data rate (bps)||Page Duration (s)||Pages in a sub-frame||Sub-frames in a frame
|-
| align="center" | F/NAV
| align="center" | E5a-I
| align="center" | 25
| align="center" | 10
| align="center" | 5
| align="center" | 12
|-
| align="center" | I/NAV
| align="center" | E1B, E5b-I
| align="center" | 125
| align="center" | 2
| align="center" | 15
| align="center" | 24
|}

This arrangement allows accomplishing the three different main categories of data to be transmitted at different rates:
* Fast rate (for urgent data, such as integrity): page.
* Medium rate (Ephemeris, Clock Correction): sub-frame.
* Slow rates (Almanacs): frame.
The page starts with a Synchronisation Word (SW) followed by the interleaving FEC (Forward Error Correction) coded navigation data and ends with tail bits for the FEC decoding. In addition both navigation messages transmit a CRC data field in order to detect corrupted data. The size of this field is different in each navigation message.
Three levels of error coding are applied to the Galileo Message Data Stream:
# A Cyclic Redundancy Check (CRC) with error detection capabilities after recovery of the received data;
# A one-half rate Forward Error Correction (FEC). Tail Bits (sequence of zeros) to allow Viterbi decoding;
# Block Interleaving on the resulting frames: provides robustness to the FEC decoding algorithm since in presence of a burst of erroneous bits it is converted into small errors in several pages. This scheme allows reducing the bit error ratio in the increased data rates.

As referred, the FEC coded symbols are transmitted interleaved within the page and because of that the navigation data can only be decoded when the complete interleaving FEC coded part is received.

The following table summarizes the parameters transmitted by FNAV and INAV messages.

[[File:Params.png|none|thumb|400px]]

As can be seen in the table above, the parameters transmitted in F/NAV and I/NAV have the same size except for signal and message specific parameters, such as "Issue of Data (IOD)" and "Navigation Data Validity and Signal Health Status". In the case of "Satellite Almanac" set, the size is also different because the set includes the "Satellite signal health status".
The Galileo ephemeris parameters are [[GPS and Galileo Satellite Coordinates Computation|Keplerian-like orbital elements as in GPS]]. The nominal period update is 3 hours, being valid for a 4 hours time interval. The 1-hour overlap interval is intended to help against short outages or delays. The Galileo Almanac is also similar to the GPS and GLONASS ones.

== F/NAV Structure ==
The F/NAV navigation message is transmitted on channel E5a-I at a rate of 25 bps. The F/NAV message structure is shown in the following figure, where the duration of each entity is indicated.

[[File:FNAV.png |none|thumb|400px]]

Each frame of the F/NAV message has a duration of 600 seconds and it is composed by 12 sub-frames. In turn, each sub-frame has a duration of 50 seconds and it is composed by 5 pages with a duration of 10 seconds. The page itself comprises 3 main fields:
* Synchronisation pattern: it is no encoded and it has a length of 12 bits and is always 101101110000 being its purpose to allow the receiver to achieve synchronisation to the page boundary; it allows the receiver to achieve synchronization to the page boundary.
* F/NAV word: has a length of 238 bits and it is the interleaved and FEC encoded part of the page that encodes the fields: Page Type (6 bits) enabling the page content identification;, Navigation Data (208 bits) and CRC (24 bits) to detect potential bit errors. The CRC is computed on the Page Type and Navigation Data fields.
* Tail: has a length of 6 bits and consists of 6 zero-values that are used to enable the completion of the FEC decoding of each page.

[[File:Fnav.png | F/NAV Navigation message structure|none|thumb|400px]]

The Page Type field identifies the broadcast page which allows the user-receivers to react accordingly and grants the possibility of changing the pages sequencing, while keeping backward compatibility. The CRC is used as the most inner mechanism of errors detection because it is computed only on the Page Type and Navigation Data fields.

Please refer to the Galileo OS SIS ICD<ref name = "GAL SIS ICD">[https://www.gsc-europa.eu/sites/default/files/sites/all/files/Galileo_OS_SIS_ICD_v2.2.pdf Galileo OS SIS ICD]</ref> for detailed analysis on the F/NAV Frame layout and page contents.

== I/NAV Structure ==

The I/NAV navigation message is transmitted on both E1B and E5b-I channels at a rate of 125 bps. The two versions of the I/NAV message are disseminated through the same structure being its content also the same but not aligned over the time.

[[File:INAV.png |none|thumb|400px]]

The I/NAV message structures for the E1B and E5b-I signals use the same page layout since the service provided on these frequencies is a dual frequency service, using frequency diversity. Only page sequencing is different, with page swapping between both components in order to allow a fast reception of the data by a dual frequency receiver. However, the frame is designed to allow receivers to work also with a single frequency.

Each frame of the I/NAV message has a duration of 720 seconds and it is composed by 24 sub-frames. In turn, each sub-frame has a duration of 30 seconds and it is composed by 15 pages with a duration of 2 seconds. The page itself is composed by 3 fields:
* Synchronisation pattern: has a length of 10 bits and is always 0101100000 being its purpose to allow the receiver to achieve synchronisation to the page boundary;
* I/NAV page part: has a length of 114 bits and it is the interleaved FEC encoded part of the page where the navigation data is conveyed.
* Tail: has a length of 6 bits and consists of 6 zero-value bits that are used to enable the completion of the FEC decoding of each page part.

The page part of the message can be even or odd and both parts are always broadcast one after the other. In channel E1B the even part is transmitted first while in channel E5b-I the even part is transmitted after. The combination of two page parts constitutes a valid set of data (Nominal Page) that has to be parsed together to get the Navigation Data. The advantage of this configuration is that a receiver decoding the I/NAV on both frequencies can decode the same pages in half the time of a single frequency receiver.

[[File:Inav.png | INAV Navigation message structure |none|thumb|400px]]

Two types of I/NAV pages are defined:
* Nominal pages: having a duration of 2 seconds transmitted sequentially in time in two parts of duration 1 second each on each of the E1B and E5b-I components. The first part of the page is denoted ‘even’ and the second one is denoted ‘odd’.
* Alert pages: having a duration of 1 second transmitted in two parts of duration 1 second each at the same epoch over the E1B and E5b-I components. Again, the first part of the page is denoted ‘even’ and the second one is denoted ‘odd’. This transmission is repeated at the next epoch but switching the two parts between the components.

Please refer to the Galileo OS SIS ICD <ref name = "GAL SIS ICD">[https://www.gsc-europa.eu/sites/default/files/sites/all/files/Galileo_OS_SIS_ICD_v2.2.pdf Galileo OS SIS ICD]</ref> for detailed analysis on the I/NAV Frame layout and page contents. Let us remark that the [[Galileo Search and Rescue Service|Galileo Search and Rescue (SAR)]] Return Link Message (RLM) is transmitted only in the E1-B component. The SAR field structure for the E1-B component in nominal mode is formatted according to the values stated in the Galileo SIS ICD<ref name = "GAL SIS ICD">[https://www.gsc-europa.eu/sites/default/files/sites/all/files/Galileo_OS_SIS_ICD_v2.2.pdf Galileo OS SIS ICD]</ref> and the Galileo SAR Service Definition Document<ref name="SAR SDD">[https://www.gsc-europa.eu/sites/default/files/sites/all/files/Galileo-SAR-SDD.pdf Galileo SAR Service Definition Document]</ref>.

[[Galileo Open Service Navigation Message Authentication | Galileo OS-NMA]] capability will be added in the Reserved 1 40 bits in E1 I/NAV message.

The Galileo OS ICD released in January 2021 <ref name = "GAL SIS ICD"/> introduces new features in parts of I/NAV message transmitted on the Galileo E1-B signal component which were previously marked as spare or reserved. This means that these improvements will provide full backwards compatibility. The new features are:
* Reduced Clock and Ephemeris Data (RedCED);
* Reed-Solomon Outer Forward Error Correction Data (FEC2);
* Secondary Synchronization Pattern (SSP).

As a result of these technical solutions, users will experience an improvement of the Galileo E1 Open Service performance in terms of Robustness and Timeliness; a significant Time To First Fix Improvement in challenging environments addressing both unassisted and assisted GNSS; backward compatibility guaranteed (no impact on legacy or non-participative receivers) and low complexity implementation within OS receivers.

The Galileo system is set to begin transmitting these new I/NAV capabilities by 2023. <ref name = "GAL SIS ICD">[https://www.gsc-europa.eu/sites/default/files/sites/all/files/Galileo_OS_SIS_ICD_v2.2.pdf Galileo OS SIS ICD]</ref>

==Notes==
<references group="footnotes"/>
The information from this article has been updated by GMV based on the applicable Galileo OS Signal-In-Space Interface Control Document (ICD).

==References==
<references/>
* Hofmann-Wellenhof, B., Lichtenegger, H., K. and Wasle, E., 2008. GNSS - Global Navigation Satellite Systems. Springer-Verlag, Wien, Austria.
* Powe, M., 2006. Introduction to Galileo. powerpoint presentation, progeny.

[[Category:Fundamentals]]
[[Category:GALILEO]]

Reference Frames in GNSS

2026-04-16T10:55:11Z

Gema.Cueto:

{{Article Infobox2
|Category=Fundamentals
|Authors=J. Sanz Subirana, J.M. Juan Zornoza and M. Hernández-Pajares, Technical University of Catalonia, Spain.
|Level=Basic
|YearOfPublication=2011
|Title={{PAGENAME}}
}}
Brief descriptions of GPS WGS-84, GLONASS PZ-90, Galileo GTRF and BeiDou Coordinate System (BDC) reference frames are provided as follows.

== [[GPS General Introduction|GPS]] reference frame WGS-84 ==

From 1987, GPS uses the World Geodetic System WGS-84, developed by the US Department of Defense (DoD) and now maintained by the US National Geospatial Intelligence Agency (NGA). WGS-84, is a unified terrestrial reference system for position and vector referencing <ref group="footnotes">The document "Modern Terrestrial Reference Systems PART 3: WGS-84 and ITRS" contains data and interesting references about WGS-84 and ITRS (http://www.ngs.noaa.gov/CORS/Articles/Reference-Systems-Part-3.pdf).</ref>. Indeed, the GPS broadcast ephemeris are linked to the position of the satellite antenna phase centre in the WGS-84 reference frame. Thus, the user receiver coordinates will be expressed in the same ECEF frame.

The initial implementation of WGS-84 was realized from a set of more than a thousand terrestrial sites, which coordinates were derived from Transit observations <ref group="footnotes">With accuracy at the level of 1-2 meters, while the accuracy of the ITRF reference stations is at the centimetre level.</ref>. Successive refinements (which also leaded to some adjustments of the fundamental constants), using more accurate coordinates of the monitor stations, approximate to some ITRS realizations. For instance, realizations WGS84(G730) <ref group="footnotes">"G" indicates that it has exclusively been obtained with GPS observations and 730 indicates the GPS week.</ref> and WGS84(G873) correspond to ITRF92 and ITRF94, respectively. The refined frame WGS84(G1150) was introduced in 2002, which agrees with ITRF2000 at the centimetre level. The most recent version is WGS-84 (G1762 <ref>[https://epsg.io/7664 WGS-84 (G1762) Information]</ref>) and was implemented on October 2013 and is aligned to the International GNSS Service (IGS) realisation of the ITRF2008<ref name="NGA">[https://earth-info.nga.mil/GandG/publications/NGA_STND_0036_1_0_0_WGS84/NGA.STND.0036_1.0.0_WGS84.pdf National Geospatial-Intelligence Agency (NGA) Standardization Document World Geodetic System 1984]</ref>.

The parameters of the WGS-84 ellipsoid are given in the following table 1:

::[[File:WGS84_Table.png|none|thumb|640px|'''''Table 1:''''' Ellipsoidal parameters WGS-84 (revised in 1997) and also in NGA Standard<ref name="NGA">[https://earth-info.nga.mil/GandG/publications/NGA_STND_0036_1_0_0_WGS84/NGA.STND.0036_1.0.0_WGS84.pdf National Geospatial-Intelligence Agency (NGA) Standardization Document World Geodetic System 1984]</ref>.]]

== [[GLONASS General Introduction|GLONASS]] reference frame PZ-90 ==

The GLONASS broadcast ephemeris are given in the Parametry Zemli 1990 (Parameters of the Earth 1990) (PZ-90) reference frame. As the WGS-84, this is an ECEF frame with a set of fundamental parameters associated (see table 2 from [GLONASS ICD, 2020]<ref name=GLONASS_ICD_2020>[https://glonass-iac.ru/upload/docs/stehos/stehos_en.pdf GLONASS ICD, 2020]</ref>).

The determination of a set of parameters to transform the PZ-90 coordinates to the ITRF97 was the target of the International GLONASS Experiment (IGEX-98). [Boucher and Altamimi, 2001] <ref>[Boucher and Altamimi, 2001] Boucher, C. and Altamimi, Z., 2001. ITRS, PZ-90 and WGS 84: current realizations and the related transformation parameters. Journal of Geodesy 75, pp. 613-619.</ref>presents a review of the IGEX-98 experiment and, as a conclusion, they suggest the following transformation <ref group="footnotes"><math>mas:</math> mili-arcseconds (<math>1 mas = 4.84813681 \cdot
10^{-9}</math> radians). <math>ppb:</math> parts per billion (<math>1 ppb=10^{-9}</math>).</ref> from <math>(x,y,z)</math> in PZ-90 to <math>(x',y',z')</math> in WGS-84, with a meter level of accuracy.

::<math>
\left [
\begin{array}{c}
x'\\
y'\\
z'\\
\end{array}
\right ]
=
\left [
\begin{array}{c}
x\\
y\\
z\\
\end{array}
\right ]
+
\left [
\begin{array}{ccc}
-3\,ppb & -353\,mas & -4\,mas\\
353\,mas & -3\,ppb & 19\,mas\\
4\,mas & -19\,mas & -3\,ppb\\
\end{array}
\right ]
\left [
\begin{array}{c}
x\\
y\\
z\\
\end{array}
\right ]
+
\left [
\begin{array}{c}
0.07\,m\\
-0.0\,m\\
-0.77\,m\\
\end{array}
\right ] \qquad\mbox{(1)}</math>

Following the notation of equation (3) in [[Transformation between Terrestrial Frames]]:

::<math>
\left (
\begin{array}{c}
x\\
y\\
z\\
\end{array}
\right )_{_{TRF2}}
=
\left (
\begin{array}{c}
x\\
y\\
z\\
\end{array}
\right )_{_{TRF1}}
+
\left (
\begin{array}{c}
T_1\\
T_2\\
T_3\\
\end{array}
\right )
+
\left (
\begin{array}{ccc}
D & -R_3 & R_2\\
R_3 & D & -R_1\\
-R_2 & R_1 & D\\
\end{array}
\right )
\left (
\begin{array}{c}
x\\
y\\
z\\
\end{array}
\right )_{_{TRF1}}</math>

the previous transformation (1) is defined by the parameters table:

::[[File:GLONASS_Table.png|none|thumb|400px]]

According to the GLONASS modernisation plan<ref>[http://gpsworld.com/directions-2014-new-horizons-of-glonass/ Directions 2014: New Horizons of GLONASS], GPS World, Denis Lyskov, Deputy Head of the Russian Space Agency, Roscosmos, December 1, 2013</ref>, the ephemeris information implementing the PZ-90.11 reference system was updated on all operational GLONASS satellites starting from 3:00 pm on December 31, 2013<ref>[https://www.glonass-iac.ru/GLONASS/stehos/stehos_en.pdf GLONASS Open Service Performance Standard ]</ref>. From this time on, the satellites are broadcasting in the PZ-90.11<ref>[http://www.glonass-iac.ru/en/content/news/?ELEMENT_ID=721 The transition to using the terrestrial geocentric coordinate system PZ-90.11 in operating GLONASS system has been implemented], Russian Federal Space Agency, Information-analytical centre, 4 April 2014</ref>. This ECEF reference frame is an updated version of PZ-90, closest to the ITRF2000.

The transformation from PZ-90.11 to ITRF2008 contains only an origin shift vector, and no rotations nor scale factor, as it is shown in equation (2) [Revnivykh, 2007]<ref>[Revnivykh, 2007] Revnivykh, S., 2007. GLONASS Status and Progress. In:
Minutes of the 47th CGSIC Meeting, Forth Worth, Texas.</ref><ref>[http://www.oosa.unvienna.org/pdf/icg/2012/template/PZ90-02_v2.pdf Global Geocentric Coordinate System Of The Russian Federation], WG D – Reference Frames, Timing and Applications, Mr. V. Vdovin and Ms. A. Dorofeeva, November 7, 2012.</ref>

::<math>
\left [
\begin{array}{c}
x\\
y\\
z\\
\end{array}
\right ]_{ITRF2008}
=
\left [
\begin{array}{c}
x\\
y\\
z\\
\end{array}
\right ]_{PZ-90.11}
+
\left [
\begin{array}{r}
0.003\,m\,\pm0.002\,m\\
0.001 \,m\,\pm0.002\,m\\
0.001 \,m\,\pm0.002\,m\\
\end{array}
\right ] \qquad\mbox{(2)}</math>

The parameters associated to the PZ-90 and PZ-90.11 are given in the next table 2 ([GLONASS ICD, 1998]<ref>[https://www.unavco.org/help/glossary/docs/ICD_GLONASS_4.0_(1998)_en.pdf GLONASS ICD, 1998]</ref> and [GLONASS ICD, 2020]<ref name=GLONASS_ICD_2020/>):

::[[File:PZ90_Table.png|none|thumb|640px|'''''Table 2:''''' Ellipsoidal parameters of PZ-90 and PZ-90.11.]]

== [[GALILEO General Introduction|Galileo]] Terrestrial Reference Frame (GTRF) ==

Next subsections provide an overview of the first realizations of Galileo Terrestrial Reference Frame, together with a description of the current applicable reference frame.

=== First Galileo Reference Frames ===

A consortium named the Galileo Geodetic Service Provider (GGSP<ref>[https://www.gsa.europa.eu/implementation-galileo-geodesy-service-provider-prototype Galileo Geodetic Service Provider in GSA website]</ref>), consisting of seven institutions under the lead of GeoForschungsZentrum Potsdam, built up a prototype for the development of the Galileo Terrestrial Reference Frame (GTRF) and the establishment of a service with products and information for the potential users under an EC 6th framework contract.

Like GPS, Galileo established a dedicated terrestrial reference frame (GTRF) as an independent realization of the international terrestrial reference system ITRS based on the estimated coordinates for each one of the Galileo Sensor Station (GSS) sites. According to Galileo requirements the three-dimensional differences of the position compared to the most recent ITRF should not exceed 3 cm (2-sigma).

Operational GTRF includes all Galileo sensor stations (GSS) and selected stations of IGS. IGS stations are used for alignment to ITRF (as GSS are not a part of it) and for densification of the network to improve the accuracy of the results.

GTRF computation includes two parts: free network adjustment including all stations (GSS and selected IGS) and network alignment to ITRF using the IGS stations.

Under GGSP project, the four first realizations of GTRF were established:

::::[[File:GTRF_Fig_1.png|none|420px]]

The network included 131 IGS stations and 13 GESS (Galileo Experimental Sensor Stations for the GIOVE mission).

::::[[File:GTRF_Fig_2.png|none|580px]]

Already the initial realization of the GTRF called GTRF07v01 was in agreement with ITRF05 up to 0.9, 0.9 and 2.7 mm for North, East, and Up respectively.

The anticipated configuration of the operational GTRF network is presented in the figure below.

::::[[File:GTRF_Fig_3.png|none|580px]]

GTRF transformation parameters to ITRF2005 are reported below.

Solution GTRF08v01, epoch 07:241, used number of ITRF2005 sites: 103

::::[[File:GTRF_Fig_4.png|none|420px]]

=== Current Galileo Terrestrial Reference Frame ===

Based on the outcomes of the previous section, the Galileo Terrestrial Reference Frame used by the Galileo system is described in the Galileo Open Service - Service Definition Document (SDD) <ref>[https://gssc.esa.int/navipedia/index.php/Galileo_Open_Service_(OS) Galileo Open Service - Service Definition Document (SDD)].</ref>. The Galileo navigation data (e.g. satellite ephemeris) is referenced to the GTRF. Accordingly, the user position coordinates derived from Galileo position solutions are referenced to GTRF.

Galileo GTRF is the independent and highly accurate realisation of the international Terrestrial Reference System based on the estimated coordinates of each one of the Galileo Sensor Station (GSS) sites. The Geodetic Reference Service Provider (GRSP) entity supports the Galileo Control Centre in realising the Galileo Terrestrial Reference Frame (GTRF).

At any time, the alignment between the GTRF and the latest physical realisation of the ITRF is such that the difference between the ITRF and the GTRF coordinates of the ITRF stations/markers used in the realisation of the GTRF is less than 3 cm (2σ). The GTRF is regularly aligned if new ITRF realisations are published. , Galileo OS user equipment needs to apply the appropriate valid transformation parameters between the latest ITRF and the desired reference frame.

== BeiDou Coordinate System (BDC) ==

The BeiDou Coordinate System (BDC) used to compute BeiDou navigation data is consistent with China Terrestrial Reference Frame (CGCS) 2000, which in turn is referred to ITRF97 with the epoch of 2000.0.

The main parameters of the reference ellipsoid are nearly the same as those defined by ITRS with the semi major axis (a), second degree harmonic coefficient (J2), and the mean angular velocity of the Earth (ω) the same as those of the ellipsoid of GRS1980. The gravitational mass (GM) constant adopts the value of WGS-84 (Wei, 2003). The flattening of the ellipsoid of BDC is f = 1/298.257222101<ref>[https://www.nap.edu/read/13292/chapter/10 Global Navigation Satellite Systems: Report of a Joint Workshop of the National Academy of Engineering and the Chinese Academy of Engineering (2012)]</ref>.

Please find below the geodetic constants and parameters of Earth Ellipsoid CGCS2000:

::::[[File:BeiDou.png|none|thumb|540px]]

==Notes==
<references group="footnotes"/>

==Credits==
This article was initially written by Technical University of Catalonia, Spain and updated by GMV to introduce the Beidou Reference Frame information according to the references.

==References==
<references/>

[[Category:GNSS Time Reference, Coordinate Frames and Orbits]]
[[Category:GPS Reference Systems]]
[[Category:GALILEO Reference Systems]]

GPS and Galileo Satellite Coordinates Computation

2026-04-16T10:52:20Z

Gema.Cueto:

GLONASS Satellite Coordinates Computation

2026-04-16T10:49:47Z

Gema.Cueto:

{{Article Infobox2
|Category=Fundamentals
|Authors=J. Sanz Subirana, J.M. Juan Zornoza and M. Hernández-Pajares, Technical University of Catalonia, Spain.
|Level=Intermediate
|YearOfPublication=2011
|Title={{PAGENAME}}
}}
The [[GLONASS General Introduction|GLONASS]] satellite coordinates shall be computed according to the specifications in the [[GLONASS General Introduction|GLONASS]]-ICD document. An accuracy level of about three meters can be reached using the algorithm provided by this ICD.

In table 1 are listed the broadcast ephemeris parameters which are used to compute [[GLONASS General Introduction|GLONASS]] satellites coordinates. Essentially, the ephemeris contain the initial conditions of position and velocity to perform the numerical integration of the [[GLONASS General Introduction|GLONASS]] orbit within the interval of measurement <math>|t - t_e| < 15</math> minutes. The accelerations due solar and lunar gravitational perturbations are also given.

::[[File: GLONASS_SV_Coord_Comp.png|none|thumb|400px|'''''Table 1:''''' GLONASS broadcast ephemeris and clock message parameters.]]

In order to compute PZ-90 [[GLONASS General Introduction|GLONASS]] satellite coordinates from the navigation message, the following algorithm must be used [GLONASS ICD, 1998] <ref> [https://www.unavco.org/help/glossary/docs/ICD_GLONASS_4.0_(1998)_en.pdf GLONASS ICD, 1998]</ref>.

== Computation equations and algorithm ==

::*''' 1. Coordinates transformation to an inertial reference frame:'''

:::- The initial conditions <math>(x(t_e),y(t_e),z(t_e),v_x(t_e),v_y(t_e),v_z(t_e))</math>, as broadcast in the [[GLONASS General Introduction|GLONASS]] navigation message, are in the ECEF Greenwich coordinate system PZ-90. Therefore, and previous to orbit integration, they must be transformed to an absolute (inertial) coordinate system using the following expressions <ref group="footnotes"> Note: Over a small integration intervals, a simple rotation of <math>\theta_{G_e}</math> angle around Z-axis is enough to perform this transformation. Nutation and precession of the earth and polar motion are a very slow processes and will not introduce significant deviations on such short integration time intervals (see [[Transformation between Celestial and Terrestrial Frames]]).</ref>:

::::'''Position:'''
:::::<math>
\begin{array}{l}
x_a(t_e)=x(t_e) \cos(\theta_{G_e}) - y(t_e) \sin (\theta_{G_e}) \\
y_a(t_e)=x(t_e) \sin(\theta_{G_e}) + y(t_e) \cos(\theta_{G_e}) \\
z_a(t_e)=z(t_e) \\
\end{array} \qquad \mbox{(1)}
</math>

::::'''Velocity:'''
:::::<math>
\begin{array}{l}
v_{x_a}(t_e)=v_x(t_e) \cos(\theta_{G_e}) - v_y(t_e) \sin (\theta_{G_e})- \omega_E \;
y_a(t_e) \\
v_{y_a}(t_e)=v_x(t_e) \sin(\theta_{G_e}) + v_y(t_e) \cos(\theta_{G_e})+\omega_E \;
x_a(t_e) \\
v_{z_a}(t_e)=v_z(t_e) \\
\end{array} \qquad \mbox{(2)}
</math>

:::- The <math>\left( X''(t_e),Y''(t_e),Z''(t_e) \right)</math> acceleration components broadcast in the navigation message are the projections of luni-solar accelerations to axes of the ECEF Greenwich coordinate system. Thence, these accelerations must be transformed to the inertial system by:

:::::<math>
\begin{array}{l}
(Jx_am+Jx_as)=X''(t_e) \cos(\theta_{G_e}) -Y''(t_e) \sin(\theta_{G_e})\\
(Jx_am+Jx_as)=X''(t_e) \sin(\theta_{G_e}) +Y''(t_e) \cos(\theta_{G_e})\\
(Jx_am+Jx_as)=Z''(t_e)\\
\end{array} \qquad \mbox{(3)}
</math>

:::Where <math>(\theta_{G_e})</math> is the sidereal time at epoch <math>t_e</math>, to which are referred the initial conditions, in Greenwich meridian:
:::::<math>
\theta_{G_e}= \theta_{G_0} + \omega_E (t_e-3\, hours) \qquad \mbox{(4)}
</math>

:::being:

:::- <math>\omega_E</math>: earth's rotation rate (<math>0.7292115\, 10^{-4}\; rad/s</math>)).
:::- <math>\theta_{G_0}</math>: the sidereal time in Greenwich at midnight GMT of a date at which the epoch <math>t_e</math> is specified. (Notice: GLONASS_time = UTC(SU) + <math>3</math> hours).

::*''' 2. Numerical integration of differential equations that describe the motion of the satellites.'''

:::According to [[GLONASS General Introduction|GLONASS]]-ICD, the re-calculation of ephemeris from epoch <math>t_e</math> to epoch <math>t_i</math> within the measurement interval (<math>|t_i-t_e|<15 min</math>) shall be performed by a numerical integration of the differential equations (5) describing the motion of the satellites. These equations shall be integrated in a direct absolute geocentric coordinate system OXa, OYa, OZa, connected with current equator and vernal equinox, using the 4th order Runge-Kutta technique:

:::::<math>
\left\{
\begin{array}{l}
\frac{dx_a}{dt}=v_{x_a}(t)\\
\frac{dy_a}{dt}=v_{y_a}(t)\\
\frac{dz_a}{dt}=v_{z_a}(t)\\
\frac{dv_{x_a}}{dt}=-\bar{\mu} \bar{x}_a +\frac{3}{2}C_{20}\bar{\mu} \bar{x}_a \rho^2(1-5 \bar{z}_a^2)+ Jx_am+Jx_as\\
\frac{dv_{y_a}}{dt}=-\bar{\mu} \bar{y}_a +\frac{3}{2}C_{20}\bar{\mu} \bar{y}_a \rho^2(1-5 \bar{z}_a^2)+ Jx_am+Jx_as\\
\frac{dv_{z_a}}{dt}=-\bar{\mu} \bar{z}_a +\frac{3}{2}C_{20}\bar{\mu} \bar{z}_a \rho^2(3-5 \bar{z}_a^2)+ Jx_am+Jx_as\\
\end{array} \qquad \mbox{(5)}
\right .
</math>

:::where:

:::::<math>\bar{\mu}=\frac{\mu}{r^2}</math>,<math>\bar{x_a}=\frac{x_a}{r}</math>, <math>\bar{y_a}=\frac{y_a}{r}</math>, <math>\bar{z_a}=\frac{x_a}{r}</math>, <math>\bar{\rho}=\frac{a_E}{r}</math>, <math>r=\sqrt{x_a^2+y_a^2+z_a^2}</math>

:::::<math>a_E= 6\,378.136\; km</math> Equatorial radius of the Earth (PZ-90).

:::::<math>\mu= 398\,600.44\; km^3/s^2</math> Gravitational constant (PZ-90).

:::::<math>C_{20}=-1\,082.63\cdot 10^{-6}</math> Second zonal coefficient of spherical harmonic expression.

:::''Note'': In the above differential equations system (5), the term <math>C_{20}=-J_2=+\sqrt{5}\bar{C}_{20}</math> is used instead of <math>J_2</math> in equations <math>
V(r,\phi,\lambda)=\frac{\mu}{r}\left[1+\frac{1}{2}\left(\frac{a_e}{r}\right)^2 J_2\;\;(1-3\sin^2 \phi) \right] </math> and <math> \mathbb{\mathbf {\ddot r}}=\nabla V+\mathbb{\mathbf k}_{sun\_moon} </math> to keep the same expressions as in the [[GLONASS General Introduction|GLONASS]]-ICD (please refer to [[Perturbed Motion]] and [[GNSS Broadcast Orbits]])

:::The right-hand side of the previous equation system (5) takes into account the accelerations determined by the central body gravitational constant <math>\mu</math>, the second zonal coefficient <math>C_{20}</math> (that characterises polar flattening of the Earth), and the accelerations due to the luni-solar gravitational perturbation.

:::'''Runge-Kutta integration algorithm'''

:::* Given the following initial value problem:
:::::<math>
\left\{
\begin{array}{c}
\frac{dy_1}{dt}=f_1(t,y_1,\cdots,y_n)\\
\vdots\\
\frac{dy_n}{dt}=f_1(t,y_1,\cdots,y_n)\\
\end{array}
\right .
\Longleftrightarrow
\mathbb{\mathbf Y}'(t)=\mathbb{\mathbf F}(t,\mathbb{\mathbf Y}(t)) \qquad \mbox{(6)}
</math>

:::::<math>\mathbb{\mathbf Y}(t_0)=[y_1(t_0), \cdots, y_n(t_0)]^T</math>, <math>\mathbb{\mathbf Y'}(t_0)=[y'_1(t_0), \cdots, y'_n(t_0)]^T</math>

:::It is desired to find the <math>\mathbb{\mathbf Y}(t_f)</math> at some final time <math>t_f</math>, or <math>\mathbb{\mathbf Y}(t_k)</math> at some discrete list of points <math>t_k</math> (for example, at tabulated intervals).

:::* The Runge-Kutta method is based in the following algorithm:
:::::<math>
\begin{array}{l}
\mathbb{\mathbf K}_1= \mathbb{\mathbf F}(t_n,\mathbb{\mathbf Y}_n)\\
\mathbb{\mathbf K}_2= \mathbb{\mathbf F}(t_n+h/2,\mathbb{\mathbf Y}_n+h \mathbb{\mathbf K}_1/2)\\
\mathbb{\mathbf K}_3= \mathbb{\mathbf F}(t_n+h/2,\mathbb{\mathbf Y}_n+h \mathbb{\mathbf K}_2/2)\\
\mathbb{\mathbf K}_4= \mathbb{\mathbf F}(t_n+h,\mathbb{\mathbf Y}_n+h \mathbb{\mathbf K}_3)\\
\mathbb{\mathbf Y}_{n+1}=\mathbb{\mathbf Y}_n+h/6(\mathbb{\mathbf K}_1+2\mathbb{\mathbf K}_2+2\mathbb{\mathbf K}_3+\mathbb{\mathbf K}_4+ O(h^5)\\
\end{array} \qquad \mbox{(7)}
</math>

:::The method is initialised with the initial conditions <math>\mathbb{\mathbf Y}(t_0)</math> and <math>\mathbb{\mathbf Y}'(t_0)</math>. For the numerical integration of [[GLONASS General Introduction|GLONASS]] satellite orbits, the function <math>\mathbb{\mathbf F}(t,\mathbb{\mathbf Y})</math> is given by (7).

::*''' 3. Coordinates transformation back to the PZ-90 reference system:'''

:::The coordinates <math>(x(t), y(t), z(t))</math>, obtained from the motion equations numerical integration, shall be transformed back to the Earth fixed reference frame PZ-90 with the following equations:

:::::<math>
\begin{array}{l}
x(t)= x_a(t) cos(\theta_G) + y_a(t) sin (\theta_G)\\
y(t)=- x_a(t) sin(\theta_G) + y_a(t) cos(\theta_G)\\
z(t)= z_a(t) \\
\end{array} \qquad \mbox{(8)}
</math>

:::where <math>\theta_G</math> is the sidereal time at Greenwich meridian at time <math>t</math>, where <math>t</math> is in GLONASS time, see equation (4) :

:::::<math>
\theta_G= \theta_{G_0} + \omega_E (t - 3~hours) \qquad \mbox{(9)}
</math>

:::::<math>
GLONASS\_time= UTC(SU)-3~hours \qquad \mbox{(10)}
</math>

:::Note that [[GLONASS General Introduction|GLONASS]] satellite coordinates are computed in PZ-90 reference system, instead of WGS-84 where the GPS coordinates have been calculated. To bring the PZ-90 coordinate system in coincidence with WGS-84 the transformation given by equation (11) must be applied (see [[Reference Frames in GNSS]]):

:::::<math>
\left [
\begin{array}{c}
x'\\
y'\\
z'\\
\end{array}
\right ]
=
\left [
\begin{array}{c}
x\\
y\\
z\\
\end{array}
\right ]
+
\left [
\begin{array}{ccc}
-3\,ppb & -353\,mas & -4\,mas\\
353\,mas & -3\,ppb & 19\,mas\\
4\,mas & -19\,mas & -3\,ppb\\
\end{array}
\right ]
\left [
\begin{array}{c}
x\\
y\\
z\\
\end{array}
\right ]
+
\left [
\begin{array}{c}
0.07\,m\\
-0.0\,m\\
-0.77\,m\\
\end{array}
\right ] \qquad \mbox{(11)}
</math>

:::The transformation from PZ-90.02 to WGS-84 (actually ITRF2000) is given by <math>\Delta x= -0.36\,m</math>, <math>\Delta y= +0.08\, m</math>, <math>\Delta z= +0.18\, m</math>, with no rotation, i.e., equation (12)<ref group="footnotes"> The PZ-90.02 was implemented in September 20th, 2007 at 18:00. (refer to [[Reference Frames in GNSS]]).</ref>:

:::::<math>
\left [
\begin{array}{c}
x\\
y\\
z\\
\end{array}
\right ]_{ITRF2000}
=
\left [
\begin{array}{c}
x\\
y\\
z\\
\end{array}
\right ]_{PZ-90.02}
+
\left [
\begin{array}{r}
-0.36\,m\\
0.08 \,m\\
0.18 \,m\\
\end{array}
\right ] \qquad \mbox{(12)}
</math>

==References==
<references/>

==Notes==
<references group="footnotes"/>

[[Category:Fundamentals]]
[[Category:GNSS Time Reference, Coordinate Frames and Orbits]]
[[Category:GLONASS]]

Power Spectral Density of the CBCS Modulation

2026-04-16T10:43:17Z

Gema.Cueto:

{{Article Infobox2
|Category=Fundamentals
|Authors=J.A Ávila Rodríguez, University FAF Munich, Germany.
|Level=Advanced
|YearOfPublication=2011
|Title={{PAGENAME}}
}}
[[CBCS Modulation|CBCS]] is a specific implementation of the [[MBOC Modulation]] which receives for this particular case the name of [Composite BOC (CBOC)]]. Thus, all the derivations of this chapter also apply for the CBOC implementation of MBOC that Galileo has selected for the [[GALILEO Signal Plan|E1 Open Service (OS)]].

The Composite Binary Coded Symbols modulation, or CBCS for short, is defined as the superposition of a BOC signal with a BCS by means of a modified and optimized Interplex scheme. This last sentence is of great importance because while CBCS specifies the way the signals are multiplexed at payload level, MBOC is more generic and does not say anything about how the time stream should look like.

In the most general case, <math>CBCS \left( [s],f_c,\rho \right)</math> represents the superposition of a <math>BOC\left(f_c,f_c\right)</math> with a <math>BCS\left( [s],f_c,\right)</math> in such a way that the BCS component has a percentage <math>\rho</math> of power with respect to the total power of the multiplexed signal. Furthermore, the vector [s] indicates the symbols that constitute the subchips of the BCS signal. Next figure depicts schematically the principle:

::::[[File:PSD_CBCS_Fig_1.png|none|thumb|420px|'''''Figure 1:''''' CBCS chip waveform as a superposition of a BOC signal and a BCS signal.]]

Unlike [[Binary Phase Shift Keying Modulation (BPSK) |BPSK]], [[Binary Offset Carrier (BOC)|BOC]] or [[Binary Coded Symbols (BCS)|BCS]], the CBCS signal is formed by 4-level sub-carriers. The mathematical definition of CBCS in the time domain:

::[[File:PSD_CBCS_Eq_1.png|none|520px]]
::[[File:PSD_CBCS_Eq_2.png|none|400px]]

where,

::* <math>A_1</math> is the amplitude of the modulation envelope, sum of the OS data and pilot signals, PRS and the Inter-Modulation product IM,
::* <math>\theta_1</math> and <math>\theta_2</math> describe the angular distance between the points of the 8-PSK modulation as depicted in Figure 2,
::* <math>S_{BOC\left(f_c,f_c\right)}\left(t\right)</math> represents the BOC(1,1) modulation with a chip rate <math>f_c</math>,
::* <math>S_{BCS\left([s],f_c\right)}\left(t\right)</math>represents the BCS([s],1) modulation with subchips vector given by [s] and chip rate <math>f_c</math>,
::* <math>S_{PRS}\left(t\right)</math> is the PRS modulation <math>BOC_{cos}\left(15,2.5\right)</math>,
::* <math>S_{IM}\left(t\right)</math> is the Inter-Modulation product signal, and
::* <math>S_D\left(t\right)</math> and <math>S_p\left(t\right)</math> are the PRN codes for the data and pilot channel of the OS.

The equation above is graphically shown in the figure below. We can recognize that compared with the BOC(1,1) Interplex baseline, two new phase states have appeared to account for the new BCS modulation waveform. Moreover, the quadrature component, namely PRS in the case of Galileo, presents a PSD that is not affected by the waveforms transmitted on the in-phase component.

::::[[File:PSD_CBCS_Fig_2.png|none|thumb|260px|'''''Figure 2:''''' Oscillation of the BOC and BCS signals in CBCS.]]

It is also of interest to note that thanks to the introduction of the additional BCS, there will always be OS signal being emitted at any time for any combination of code chips. This makes the modulation more efficient and reduces the IM power consequently.

Let us now look at the data and pilot channels of the Open Service in detail. In fact, recalling the CBCS time definition, we can easily separate the data and pilot channels as follows:

::[[File:PSD_CBCS_Eq_3.png|none|520px]]

The autocorrelation of a signal that is stationary in wide sense adopts the following form:

::[[File:PSD_CBCS_Eq_4.png|none|480px]]

According to this, the autocorrelation function of the data channel can be expressed as

::[[File:PSD_CBCS_Eq_5.png|none|800px]]

Where <math>p_{T_c}^{BOC\left(f_c,f_c\right)}</math> and <math>p_{T_c}^{BCS\left([s],f_c\right)}</math> represent the chip waveforms of <math>BOC\left(f_c,f_c\right)</math> and <math>BCS\left([s],f_c\right)</math> correspondingly. This formulation can be further developed if the expectation operator is expressed in integral form as shown next:

::[[File:PSD_CBCS_Eq_6.png|none|800px]]

or equivalently:

::[[File:PSD_CBCS_Eq_7.png|none|800px]]

If we further assume that the data codes show ideal properties, then <math>\mathfrak{R}_{C_D}\left(m\right)=\delta \left(m\right)</math> and the autocorrelation of the data channel yields then:

::[[File:PSD_CBCS_Eq_8.png|none|600px]]

We can repeat now the same steps for the pilot channel and arrive to a similar expression for the pilot autocorrelation:

::[[File:PSD_CBCS_Eq_9.png|none|600px]]

Comparing the autocorrelation of the pilot OS with that of the data channel, we can recognize that there is only a sign difference in the cross-correlation term, which is in phase for the data channel and in anti-phase for the pilot channel. Now that we have derived the expressions for the data and pilot autocorrelations of the Open Service, the Power Spectral Densities of both channels can be obtained in the following form:

::[[File:PSD_CBCS_Eq_10.png|none|780px]]

which can be simplified as shown next:

::[[File:PSD_CBCS_Eq_11.png|none|640px]]

or equivalently:

::[[File:PSD_CBCS_Eq_12.png|none|540px]]

According to this, the power of the data channel will be

::[[File:PSD_CBCS_Eq_13.png|none|460px]]

where, the cross-correlation between <math>BOC\left(f_c,f_c\right)</math> and <math>BCS\left([s],f_c\right)</math> is defined as follows:

::[[File:PSD_CBCS_Eq_14.png|none|640px]]

If we solve now for the pilot channel, it can be shown that the power spectral density of the pilot OS will be:

::[[File:PSD_CBCS_Eq_15.png|none|640px]]

or expressed in terms of the power spectral density,

::[[File:PSD_CBCS_Eq_16.png|none|580px]]

such that

::[[File:PSD_CBCS_Eq_17.png|none|480px]]

If we sum up now the power spectral densities of the data and pilot channels as given by (12) and (16), we obtain the general power expression for the power of the composite OS:

::[[File:PSD_CBCS_Eq_18.png|none|580px]]

Thus, the total power of the OS signal, with data and pilot together, will be:

::[[File:PSD_CBCS_Eq_19.png|none|340px]]

adopting the normalized expression of the OS power spectral density the following form:

::[[File:PSD_CBCS_Eq_20.png|none|660px]]

Since the phase states are sitting on the circle and the power spectral densities of the data and pilot channels are normalized to infinite bandwidth, we can express the normalized power spectral density of the OS signal as follows:

::[[File:PSD_CBCS_Eq_21.png|none|560px]]

If we have a close look at the expression above, we can see that we can express the percentage of power that falls on the BCS signal as follows:

::[[File:PSD_CBCS_Eq_22.png|none|280px]]

Thus,

::[[File:PSD_CBCS_Eq_23.png|none|480px]]

This means, that the total OS power spectral density can be defined as the linear combination of the PSDs of the two waveforms composing the CBCS signal, namely <math>BOC\left(f_c,f_c\right)</math> and <math>BCS\left([s],f_c\right)</math>, weighted by the percentage <math>\rho</math> of power that is put on the BCS component.

If we divide now the expressions of the data and pilot power spectral densities given in (12) and (16) by the integrated data and pilot power, we obtain the normalized expressions:

::[[File:PSD_CBCS_Eq_24.png|none|560px]]

where r indicates the correlation between <math>BOC\left(f_c,f_c\right)</math> and <math>BCS\left([s],f_c\right)</math> for zero offset. Equally, for the pilot channel we would have:

::[[File:PSD_CBCS_Eq_25.png|none|560px]]

Another expression of interest is the power spectral density of the data and pilot channels with respect to the total OS power. Equally interesting is also to obtain the power of the <math>BOC\left(f_c,f_c\right)</math> and <math>BCS\left([s],f_c\right)</math> component with respect to the total OS power. We derive next the corresponding expressions.

Let us study first the power of the data channel with respect to the total OS channel. Indeed, if we divide (13) by (18), we obtain the next relationship:

::[[File:PSD_CBCS_Eq_26.png|none|600px]]

Equally, the percentage of pilot OS power with respect to the total OS power is:

::[[File:PSD_CBCS_Eq_27.png|none|600px]]

To calculate the total power on the <math>BOC\left(f_c,f_c\right)</math> signal, we can use the equation (1) and thus,

::[[File:PSD_CBCS_Eq_28.png|none|300px]]

so that the percentage of <math>BOC\left(f_c,f_c\right)</math> power with respect to the total OS power will adopt the following form:

::[[File:PSD_CBCS_Eq_29.png|none|420px]]

If we repeat now for the BCS component,

::[[File:PSD_CBCS_Eq_30.png|none|300px]]

and normalizing (30) to the total OS power, we have the percentage <math>\rho</math> of power on the BCS component:

::[[File:PSD_CBCS_Eq_31.png|none|360px]]

In the same manner, the useful power of the PRS for the quadrature signal can be easily obtained from the signal definition shown at the beginning of this article. In fact:

::[[File:PSD_CBCS_Eq_32.png|none|300px]]

Equally, for the Inter-Modulation Product we can derive a similar expression:

::[[File:PSD_CBCS_Eq_33.png|none|300px]]

Finally, if we sum up the power of all the desired signals plus the Inter-Modulation term, we find as expected that the CBCS modulation has constant envelope of amplitude <math>A_1</math>:

::[[File:PSD_CBCS_Eq_34.png|none|240px]]

It is interesting to note that while for the <math>BOC\left(f_c,f_c\right)</math> Interplex the inter-modulation power only depends on one modulation index, namely m, in the case of CBCS both indexes <math>\theta_1</math> and <math>\theta_2</math> have to be considered. This means in other words that fixing the IM power is easier with CBCS than it would be if only a <math>BOC\left(f_c,f_c\right)</math> were transmitted. The result is thus a more efficient control of the IM power since we have more degrees of freedom to play.

One final but important comment is that Interplex with only <math>BOC\left(f_c,f_c\right)</math> can be easily described taking <math>\theta_2</math> equal to π/2.

Once the most important equations describing CBCS have been derived, we study next how to calculate the multiplex parameters when we fix the percentage of power on the BCS component, the power split between data and pilot and the power split between the different signals. Moreover, it is important to note that the expressions derived above were obtained for infinite bandwidth differing thus the results slightly when filtering effects are considered.

According to the [Galileo SIS ICD, 2025]<ref>[https://www.gsc-europa.eu/sites/default/files/sites/all/files/Galileo_OS_SIS_ICD_v2.2.pdf Galileo Open Service Signal In Space Interface Control Document (OS SIS ICD), 2025]</ref> the power split between the OS data and pilot signals shall be 50/50 while the open signals and PRS should have the same power levels. The resulting equations system to solve is then:

::[[File:PSD_CBCS_Eq_35.png|none|340px]]

where the first equation indicates the amount of power that is moved from <math>BOC\left(f_c,f_c\right)</math> to the BCS signal and the second and third equations represent the power ratios between the different signals. We can also observe that the equations above do not depend on the specific BCS vector [s] since they only account for power relationships. Nonetheless, as it could be expected, the real BCS vector plays indirectly an outstanding role in assessing if one signal is compatible with the rest of signals in the band or not. In fact, depending on how the specific BCS sequence looks like, the spectral overlapping with the other signals around will be different, determining thus the maximum amount of power <math>\rho</math> that can be put on its BCS part in order not to interfere.

Until now we have analyzed the case when the BCS signal is on both the data and pilot channels as this is the baseline of Galileo for the OS. Nevertheless, for some specific applications, allocating the high frequency components (thus the BCS signal) only on the pilot channel could be of interest. Indeed, the GPS implementation of MBOC, namely TMBOC, goes in this direction.

In order to have all the power of the BCS signal only on the pilot channel and still maintain constant envelope, the expression of the CBCS modulation has to be generalized. Accordingly, (1) and (2) can be slightly modified as shown next:

::[[File:PSD_CBCS_Eq_36.png|none|640px]]

where the constants <math>k_1</math>,<math>k_2</math>,<math>k_3</math> and <math>k_4</math> are calculated from

::* the power split between data and pilot,
::*the relationship of powers between OS and PRS,
::*the percentage of power on the BCS signal with respect to the total OS power under the constraint that the phase points are on the unit circle, and
::* accounting for the different filter losses of the signals due to bandlimiting.

Mathematically, all these conditions can be expressed as follows

::[[File:PSD_CBCS_Eq_37.png|none|260px]]

where:
::* <math>\rho</math> is the percentage of power on the BCS signal,
::* <math>\xi</math> indicates the percentage of power that falls onto the pilot channel with respect to the data channel. Thus, if we have a power split of 50/50, <math>\xi = 1</math> and for 75/25, <math>\xi = 3</math>,
::* and <math>\beta</math> indicates the power difference between PRS and OS in dB, accounting for the different filter losses of both signals due to satellite bandlimiting.

It should be noted that this calculation ignores the effect of the correlation between the <math>BOC\left(f_c,f_c\right)</math> and <math>BCS\left([s],f_c\right)</math>, which is introduced by virtue of the satellite bandlimiting. Additionally, since all the phase points have to be on the unit circle, we have:

::[[File:PSD_CBCS_Eq_38.png|none|500px]]

since the real component of the signal takes 8 values with equal probability, given as shown in the following table:

::::[[File:PSD_CBCS_Table_1.png|none|thumb|420px|'''''Table 1:''''' Value of the signal <math>s\left(t\right)</math> as a function of the different code inputs.]]

Additionally, the IM component <math>IM=\left \{IM_1,IM_2,\cdots,IM_8 \right \}</math> must take the appropriate value to bring the phase plots to the unit circle. Note that this is true independently of the BCS component is in phase or in anti-phase. Finally, an extra constraint comes from the necessary condition that the Inter-Modulation signal has zero mean:

::[[File:PSD_CBCS_Eq_39.png|none|300px]]

If we put all the conditions together, we can see that we have totally twelve equations, namely (37), (38) and (39), and twelve unknowns to find, namely , <math>k_1</math>,<math>k_2</math>,<math>k_3</math> and <math>k_4</math>. Unfortunately, while (36) covers more cases than (1) and (2), in general it is not possible to find an explicit expression for the coefficients <math>k_1</math>,<math>k_2</math>,<math>k_3</math> and <math>k_4</math>.

We show next with an example how the parameters of the CBCS multiplex could be obtained for the hypothetical case that the CBOC implementation of MBOC would allocate the whole BOC(6,1) component on the pilot OS signal. The power ratio between the BCS signal, in this particular case BOC(6,1), and the total OS power is 1/11 at generation. This means that in reality the power after filtering in the satellite will be slightly lower on BOC(6,1). Moreover, let us assume that the PRS power would be 2 dB above the OS power at user level and that the effect of filtering in the satellite is also taken into account. This assumption is different from the baseline when OS and PRS have the same power.

If we solve now for CBOC(6,1,1/11) with all the BOC(6,1) power on the pilot channel, with equal power for pilot and data, with 1/11 of the OS power in the BOC(6,1) before bandlimiting, the composite signal may be defined by

::[[File:PSD_CBCS_Eq_40.png|none|840px]]

where the signal <math>sc_{IM}\left(t\right)</math> is given by:

::[[File:PSD_CBCS_Eq_41.png|none|360px]]

adopting <math>a_{\left | I \right \vert _s}</math> the following values:

::::[[File:PSD_CBCS_Table_2.png|none|thumb|420px|'''''Table 2:''''' Values of the Inter-Modulation Signal (IM) to achieve a constant envelope.]]

We show the Inter-Modulation signal next graphically:

::::[[File:PSD_CBCS_Fig_3.png|none|thumb|420px|'''''Figure 3:''''' Inter-Modulation Signal necessary to have a constant envelope when BOC(6,1) is only on the pilot channel.]]

The phase states of the constellation are equally shown in the next figure. As we can see, the main effect is that the number of states has duplicated, what is of course a clear drawback. In addition, it is important to realize that this implementation of CBOC is not compliant with the MBOC spectrum definition since a cross term appears.

::::[[File:PSD_CBCS_Fig_4.png|none|thumb|260px|'''''Figure 4:''''' CBOC 16-PSK modulation that results when all the BOC(6,1) component is placed on the pilot channel.]]

==References==
<references/>

== Credits ==
The information presented in this NAVIPEDIA’s article is an extract of the PhD work performed by Dr. Jose Ángel Ávila Rodríguez in the FAF University of Munich as part of his Doctoral Thesis “On Generalized Signal Waveforms for Satellite Navigation” presented in June 2008, Munich (Germany)

[[Category:Fundamentals]]
[[Category:GNSS Signals]]

GPS Signal Plan

2026-04-16T10:40:42Z

Gema.Cueto:

{{Article Infobox2
|Category=GPS
|Authors=J.A Ávila Rodríguez, University FAF Munich, Germany.
|Level=Advanced
|YearOfPublication=2011
|Title={{PAGENAME}}
}}
== GPS L1 Band ==

The GPS L1 band (1575.42 MHz) has turned to be the most important band for navigation purposes. Indeed most of the applications in the world nowadays are based on the signals transmitted at this frequency. Three signals are transmitted at the moment by GPS in L1: C/A Code, P(Y) Code,M-Code and the new L1C signal, which is in the process of being fielded as L2C and L5. The legacy civil signal, called L1 C/A or C/A at L1, will continue broadcasting in the future. We describe all of these signals modulated in the L1 RF carrier frequency in the next lines:

* The Coarse/Acquisition (C/A) code signal was primarily thought for acquisition of the P (or Y) code and has become nowadays the most important signal for mass market applications. The PRN C/A Code for SV ID number i is a Gold code, <math>G_i (t) </math>, of 1 millisecond in length at a chipping rate of 1.023 Mbps. The <math>G_i (t) </math> sequence is a linear pattern generated by the Modulo-2 addition of two subsequences, <math>G_1</math> and <math>G_{1i}</math>, each of them being a 1023 chip long linear pattern. The epochs of the Gold code are synchronized with the <math>X_1</math> epochs of the P-code.

* The P Code is the precision signal and is coded by the precision code. Moreover the Y-Code is used in place of the P-code whenever the Anti-Spoofing (A/S) mode of operation is activated as described in the ICDs 203, 224 and 225. The PRN P-code for SV number i is a ranging code, Pi(t), 7 days long at a chipping rate of 10.23 Mbps. The 7 day sequence is the Modulo-2 sum of two sub-sequences referred to as <math>X_1</math> and <math>X_{2i}</math> with 15,345,000 chips and 15,345,037 chips, respectively. The <math>X_{2i}</math> sequence is an <math>X_2</math> sequence selectively delayed by 1 to 37 chips allowing the basic code generation technique to produce a set of 37 mutually exclusive P-code sequences 7 days long.

* The modernized military signal (M-Code) is designed exclusively for military use and is intended to eventually replace the P(Y) code [E. D. Kaplan and C. Hegarty, 2006]<ref>[E. D. Kaplan and C. Hegarty, 2006] E. D. Kaplan and C. Hegarty, Understanding GPS: Principles and Applications-2nd Edition, Chapter 4.</ref>. The M-Code provides better jamming resistance than the P(Y) signal, primarily through enabling transmission at much higher power without interference with C/A code or P(Y) code receivers [B.C. Barker et al., 2000]<ref>[B.C. Barker et al., 2000] B.C. Barker, J.W. Betz, J.E. Clark, J.T. Correia, J.T. Gillis, S. Lazar, Lt. K. A. Rehborn, J.R. Straton, III, ARINC, Overview of the GPS M-Code Signal, Proceedings of the National Technical Meeting of the Institute of Navigation, ION-NTM 2000, 26-28 January 2000, Anaheim, California, USA.</ref>. Moreover, the M-Code provides more robust signal acquisition than is achieved today, while offering better security in terms of exclusivity, [[GNSS Authentication and encryption | authentication]], and confidentiality, along with streamlined key distribution. In other aspects, the M-Code signal provides much better performance than the P(Y) Code and more flexibility.

* The new L1 Civil signal (L1C), defined in the [GPS ICD-800]<ref name="GPS_SIS_ICD_800">[https://archive.gps.gov/technical/icwg/IRN-IS-800J-003.pdf GPS ICD-800 "Navstar GPS Space Segment/User Segment L1C Interfaces"]</ref>, has been designed for interoperability with Galileo E1. It is compatible with current L1 signal but broadcast at a higher power level and includes advanced design for enhanced performance. It consists of two main components; one denoted <math>L1C_P</math> to represent the pilot signal, consisting of a time-multiplexing of BOC(1,1) and BOC(6,1), thus without any data message, and <math>L1C_D</math>, with a pure BOC(1,1), for the data channel. This is spread by a ranging code and modulated by a data message. The pilot channel <math>L1C_P</math> is also modulated by an SV unique overlay secondary code, <math>L1C_O</math>. An enhancement to this L1C signal is being analysed, which is called CHIMERA (Chips Message Robust Authentication). This technique consists on adding encrypted watermarks to the L1C signal that not only let users know when a signal is being spoofed but also makes it possible to [[GNSS Authentication and encryption | authenticate]] the location of a GPS receiver to another party.

For more details on the code generation refer to the [GPS ICD 200]<ref name="GPS_SIS_ICD_200">[https://archive.gps.gov/technical/icwg/IRN-IS-200N-003.pdf GPS ICD-200 "Navstar GPS Space Segment/User Segment Interfaces"]</ref> and [GPS ICD-800]<ref name="GPS_SIS_ICD_800"></ref>. Finally, the technical characteristics of the existing GPS signals in the L1 band are summarized in the following Table 1.

::::[[File:Chapter_2_Table_1.png|none|thumb|520px|'''''Table 1:''''' GPS L1 signal technical characteristics.]]

Of all the signals above, the C/A Code is the best known as most of the receivers that have been built until today are based on it. The C/A Code was open from the very beginning to all users, although until May 1st, 2000 an artificial degradation was introduced by means of the Select Availability (SA) mechanism which added an intentional distortion to degrade the positioning quality of the signal to non-desired users. As we have already mentioned, the C/A Code was thought to be an aid for the P(Y) Code (to realize a Coarse Acquisition). The M-Code is the last military signal that has been introduced in GPS.

For a long time different signal structures for the M-Code were under consideration [J.W. Betz, 2001] <ref>[J.W. Betz, 2001a] J.W. Betz, Binary Offset Carrier Modulations for Radionavigation, NAVIGATION: Journal of The Institute of Navigation Vol. 48, No. 4, Winter 2001/02</ref>being the Manchester code signals (BPSK) and the binary offset carrier (BOC) signals the two favored candidates. Both solutions result from the modulation of a non-return to zero (NRZ) pseudo random noise spreading code by a square-wave sub-carrier. While the Manchester code has a spreading code of rate equal to that of the square-wave, the BOC signal does not necessarily have to be so, being the only constraint that the rate of the spreading code must be less than the sub-carrier frequency.

The interesting aspect about these signals is that, like the conventional sub-carrier modulation, the waveform presents a zero at the carrier frequency due to the square-wave sub-carrier. In fact, their split-power spectra clearly facilitate the compatibility of the GPS military M-Code signal with the existing C/A Code and P(Y) Code.

::::[[File:Chapter_2_Spectra_GPS_Signals_L1.png|none|thumb|520px|'''''Figure 1:''''' Spectra of GPS Signals in L1.]]

We can clearly recognize that GPS L1C concentrates more power at higher frequencies – due to BOC(6,1) – in the pilot channel than in the data channel (please refer to [[Time-Multiplexed BOC (TMBOC)]] for further details).

Finally, it is important to note that for all the figures next the commonly used expressions for bandwidths in MHz must be understood as multiplied by the factor 1.023. Thus BPSK(10) refers in reality to a BPSK signal with a chip rate of 10.23 MHz. This remains valid for all the bandwidths in this thesis, unless different stated.

== GPS L2 Band ==
GPS is transmitting in the L2 band (1227.60 MHz) a modernized civil signal known as L2C designed specifically to meet commercial needs as it enables the development of dual-frequency solutions; together with the P(Y) Code and the M-Code. The P(Y) Code and M-Code were already described shortly in the previous chapter and the properties and parameters are thus similar to those in the L1 band. In addition, for Block IIR-M, IIF, and subsequent blocks of SVs, two additional PRN ranging codes are transmitted. They are the L2 Civil Moderate (L2 CM) code and the L2 Civil Long (L2 CL) code. These two signals are time multiplexed so that the resulting chipping rate is double as high as that of each individual signal. We further describe them in the next lines more in detail:

* L2 CM Code is transmitted in the IIR-M, IIF, III and subsequent blocks. The PRN L2 CM Code for SV number i is a ranging code, <math>CM_i(t)</math>, which is 20 milliseconds in length at a chipping rate of 511.5 Kbps. The epochs of the L2 CM Code are synchronized with the X1 epochs of the P-code. The <math>CM_i(t)</math> sequence is a linear pattern which is short cycled every count period of 10,230 chips by resetting with a particular initial state. Furthermore, for Block IIR-M, the navigation data is also Modulo-2 added to the L2 CM Code. It is interesting to note that the navigation data can be used in one of two different data rates selectable by ground command:

::* D(t) with a data rate of 50 bps
::* D(t) with a symbol rate of 50 symbols per second (sps) which is obtained by encoding D(t) with a data rate of 25 bps coded in a rate 1/2 convolutional code. Finally, the resultant bit-train is combined with the L2 CL Code using time-division multiplexing.

* L2 CL Code is transmitted in the IIR-M, IIF, III and subsequent blocks. The PRN L2 CL Code for SV number is a ranging code, <math>CL_i(t)</math>, which is 1.5 seconds in length at a chipping rate of 511.5 Kbps. The epochs of the L2 CL Code are synchronized with the X1 epochs of the P Code. The <math>CL_i(t)</math> sequence is a linear pattern which is generated using the same code generator polynomial as of <math>CM_i(t)</math>. However, the <math>CL_i(t)</math> sequence is short cycled by resetting with an initial state every count period of 767,250 chips.

Finally, it is important to note that the GPS L2 band will have a transition period from the C/A Code to L2C and mixed configurations could occur. Next figure shows the baseband L2 signal generation scheme. As we can recognize, although the chipping rate of the L2 CM and L2 CL signals is of 511.5 Kbps individually, after the time multiplexing the composite signal results in a stream of 1.023 MHz.

::::[[File:Chapter_2_Modulation_scheme_GPS_L2_Signals.png |none|thumb|520px|'''''Figure 2:''''' Modulation scheme for the GPS L2 Signals.]]

The technical characteristics of the GPS L2 signals are summarized next:

::::[[File:Chapter_2_Table_2.png |none|thumb|520px|'''''Table 2:''''' GPS L2 signal technical characteristics.]]

The spectra of the different signals described in the preceding lines are shown in the next Figure 3:

::::[[File:Chapter_2_Spectra_GPS_Signals_L2.png|none|thumb|520px|'''''Figure 3:''''' Spectra of the GPS Signals in L2.]]

==GPS L5 Band==
The GPS L5 (1176.45 MHz) signal is one of the new signals belonging to the GPS modernization plan. It is broadcast in a radio band reserved exclusively for aviation safety services and the signal is thought to be used in combination with L1 C/A to improve accuracy (via ionospheric correction) and robustness (via signal redundancy). It is transmitted at a higher power level than current civil GPS signals, has a wider bandwidth and has lower frequency which enhances reception for indoor users.

The L5 signal consists of two carrier components that are in phase quadrature with each other. Each carrier component is bi-phase shift key (BPSK) modulated by a separate bit train. One bit train is module-2 sum of the I5-code, NAV data, and synchronization sequence while the other is the Q5-code with no NAV data, but with another synchronization sequence. For a particular SV, all transmitted signal elements (carriers, codes, synchronization sequence and data) are coherently and derived from the same on-board frequency source.

The L5 data channel and the L5 pilot channel are the two carrier frequencies. Moreover, two PRN ranging codes are transmitted on L5. The PRN L5-codes for SV number i are independent, but time synchronized ranging codes ,<math>X_I^i(t) </math> and <math> X_Q^i(t) </math>, of 1 millisecond in length at a chipping rate of 10.23 Mbps [GPS ICD-705]<ref name="GPS_SIS_ICD_705">[https://archive.gps.gov/technical/icwg/IRN-IS-705J-003.pdf GPS ICD-705 "Navstar GPS Space Segment/User Segment L5 Interfaces"]</ref>. For each code, the 1-millisecond sequences are the modulo-2 sum of two sub-sequences referred to as XA and XBi with lengths of 8,190 chips and 8,191 chips respectively, which restart to generate the 10,230 chip code. The XBi sequence is selectively delayed, thereby allowing the basic code generation technique to produce the different satellite codes.

The generation scheme can be shown graphically as follows:

::::[[File:Chapter_2_Modulation_scheme_GPS_L5_Signals.png |none|thumb|520px|'''''Figure 4:''''' Modulation scheme for the GPS L5 Signals.]]

For more details on L5, refer to [E. D. Kaplan and C. Hegarty, 2006]. The different signals present the following spectrum:

::::[[File:Chapter_2_Spectra_GPS_Signals_L5.png|none|thumb|520px|'''''Figure 5:''''' Spectra of the GPS Signals in L5.]]

To conclude, the technical characteristics of the GPS signals in L5 can be summarized as follows:

::::[[File:Chapter_2_Table_3.png |none|thumb|520px|'''''Table 3:''''' GPS L5 signal technical characteristics.]]

== GPS Modernization ==

Before December 2005 the basic GPS capability consisted of the Standard Positioning Service (SPS) provided by the C/A Code on the L1 frequency and the Precise Positioning Service (PPS) provided by the P(Y) Code on L1 and L2. Although those services are of relatively good quality, the United States proposed a [[GPS_Future_and_Evolutions|modernization plan]] in order to improve the quality and protection of both civil and military users which includes, among other features, the provision of additional signals (e.g. L5, L1C). These signals are being gradually deployed in the GPS system while the constellation is being renewed.

==References==
<references/>

== Credits ==
The information presented in this NAVIPEDIA’s article is an extract of the PhD work performed by Dr. Jose Ángel Ávila Rodríguez in the FAF University of Munich as part of his Doctoral Thesis “On Generalized Signal Waveforms for Satellite Navigation” presented in June 2008, Munich (Germany)

The information of this article is regularly updated in line with the GPS modernization plan updates. Applicable GPS ICD documents can be found in https://www.gps.gov/technical/icwg/
[[Category:GNSS Signals]]
[[Category:GPS]]
[[Category:GPS Signal Structure]]

GNSS Interference Model

2026-04-16T10:37:36Z

Gema.Cueto:

{{Article Infobox2
|Category=Fundamentals
|Authors=J.A Ávila Rodríguez, University FAF Munich, Germany.
|Level=Advanced
|YearOfPublication=2011
|Title={{PAGENAME}}
}}
In this article we present the most important expressions that are necessary to assess the degradation that a signal causes on another signal in the shared band. As we have shown in [[MBOC Modulation]], the methodology is based on the idea of measuring the degradation of a desired signal in terms of the reduction of its effective C/N0 (this figure is also analysed in [[Equivalent Carrier to Noise Ratio in presence of RF interference|Equivalent C/N0 in presence of Interference]]). This can be caused by either the background noise where all the non GNSS signals are included or by another interfering signal of the same or similar nature. To this group belong all the types of interference from other GNSS signals. We can further distinguish the different GNSS interference sources following this classification:

:* <math>I_{Intra}</math>: This type of interference is commonly known as intra-system interference and is due to the signals coming from satellites that belong to the same system as the desired signal.
:* <math>I_{Interop}</math>: This type of interference corresponds to the equivalent noise introduced in the receiver by an interfering signal coming from a satellite of a different constellation but with the same signal structure as that of the desired signal.
:* <math>I_{Inter}</math>: This type of interference comes from signals with a different signal structure no matter whether the signal belong to the same system or a different one.

If we put now all the GNSS sources of interference together, we have as interfering power:

::[[File: IM_Eq_1.png|none|340px]]

[[Category:Fundamentals]]
[[Category:GNSS Signals]]

Moreover, we define the equivalent noise power density of each of the interfering signals as:

::[[File: IM_Eq_2.png|none|340px]]

:where
:* <math>X</math> defines the type of interference according to the definitions above,
:* <math>N_X</math> represents the number of satellites,
:* <math>C_j</math> is the received power of satellite j,
:* <math>\Beta_r</math> is the receiver bandwidth,
:* <math>G_d</math> is the power spectral density of the desired signal s,
:* <math>f_{dop-s}</math> is the doppler frequency offset of the desired signal s,
:* <math>K_{js}</math> is the spectral separation coefficient between signal j and the desired signal s. This is defined as follows:

::::[[File: IM_Eq_3.png|none|520px]]

:where,
:* <math>G_j^i(f)</math> is the power spectral density of the interfering signal j
:* <math>f_{dop_s}</math> is the doppler frequency offset of the desired signal j.

The GNSS receiver of our model is supposed to stay stationary at the earth’s surface so that only the motion of the satellites will be responsible for the Doppler offsets observed at user level. Moreover, we know that while for GPS the absolute Doppler frequency offset does not exceed 4.4 kHz, the range is narrower for Galileo, being the maximum value of 3.3 kHz in the E1/L1 band as shown in Figure 1 [S. Wallner et al., 2005] <ref name="SW_2005">[S. Wallner et al., 2005] S. Wallner, G.W. Hein, J.-A. Avila Rodriguez, T. Pany, A. Posfay, Interference Computations Between GPS and Galileo, Proceedings of the International Technical Meeting of the Institute of Navigation, ION-GNSS 2005, 13-16 September, 2005, Long Beach, California, USA.</ref>:

::::[[File:IM_Fig_1.png|none|thumb|580px|'''''Figure 1:''''' Histogram of the Doppler Frequency Offsets for GPS and Galileo E1/L1.]]

Once we have defined mathematically the shape of the different sources of interference, we can now compute the degradation suffered by a receiver due to other signals. As we said at the beginning, the interference of one system onto another one is given by the reduction of the effective <math>C/N_0</math>, which can be expressed as follows:

::[[File: IM_Eq_4.png|none|340px]]

where N0 refers to the noise floor. Furthermore, we assume a noise value of -201.5 dBW/Hz for all the purposes. In addition, the degradation of the effective <math>C/N_0</math> due to intra-system interference can be thus expressed as follows:

::[[File: IM_Eq_5.png|none|420px]]

Equally, for the case of the degradation caused by the inter-system interference we have the following expression:

::[[File: IM_Eq_6.png|none|680px]]

Now that we have the necessary mathematical expressions to calculate the degradation suffered by a receiver according to this simplified model, we only need to obtain the power of the desired and interfering signals at each point of the earth. To do that, we have to simulate the satellite positions and movements and account for the attenuations of the signal from the satellite to the receiver. Indeed, once we know the minimum received powers as given in [Galileo SIS ICD, 2025] <ref>[https://www.gsc-europa.eu/sites/default/files/sites/all/files/Galileo_OS_SIS_ICD_v2.2.pdf Galileo Open Service Signal In Space Interface Control Document (OS SIS ICD), 2025]</ref>, [GPS ICD 200]<ref>[https://archive.gps.gov/technical/icwg/IRN-IS-200N-003.pdf IS-GPS-200, IRN-200D-001:NAVSTAR GLOBAL POSITIONING SYSTEM Navstar GPS Space Segment/Navigation User Interface, 2024]</ref>, [GPS ICD-705, 2024] <ref>[https://archive.gps.gov/technical/icwg/IRN-IS-705J-003.pdf IS-GPS-705, IRN-705-003:Navstar GPS Space Segment/User Segment L5 Interfaces, 2024]</ref> and [GPS ICD-800, 2006] <ref>[https://archive.gps.gov/technical/icwg/IRN-IS-800J-003.pdf IS-GPS-800 Navstar GPS Space Segment/User Segment L1C Interfaces, 2024]</ref> we obtain the transmission power Pj of each satellite as done by [S. Wallner et al., 2005] <ref name="SW_2005"/> and we can derive the power received at user level at every point of the earth according to:

::[[File: IM_Eq_7.png|none|540px]]

:where
:* <math>P_j</math> depicts the transmission power from satellite j,
:* <math>G_j</math> is the satellite antenna gain,
:* <math>A_dist</math> is the attenuation due to the distance between the satellite and the user,
:* <math>A_pol</math> is the attenuation of the signal due to the mismatch losses in the polarization,
:* <math>A_atm</math> is the attenuation of the signal due to the atmosphere, and
:* <math>G_user</math> is the receiver antenna gain.

The satellite antenna gain <math>G_i</math> Gj is a function of the Off-Boresight Angle <math>\alpha</math> as defined next:

::::[[File:IM_Fig_2.png|none|thumb|580px|'''''Figure 2:''''' Definition of Off-Boresight Angle.]]

being the typical satellite antenna gain as shown in the following figure:

::::[[File:IM_Fig_3.png|none|thumb|580px|'''''Figure 3:''''' Assumed Typical Satellite Antenna Gain.]]

Additionally, the signal attenuation due to the free-space losses <math>A_dist</math> is given by:

::[[File: IM_Eq_8.png|none|240px]]

:where,
:*<math>c</math> c is the speed of light
:*<math>d</math> d is the distance between the satellite and the user
:*and <math>f_c</math> is the carrier frequency

==References==
<references/>

== Credits ==
The information presented in this NAVIPEDIA’s article is an extract of the PhD work performed by Dr. Jose Ángel Ávila Rodríguez in the FAF University of Munich as part of his Doctoral Thesis “On Generalized Signal Waveforms for Satellite Navigation” presented in June 2008, Munich (Germany)

[[Category:Fundamentals]]
[[Category:GNSS Signals]]