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{{Article Infobox2
{{Article Infobox2
|Category=EGNOS
|Category=EGNOS
|Title={{PAGENAME}}
|Editors=GMV
|Authors=GMV.
|Level=Basic
|Level=Basic
|YearOfPublication=2011
|YearOfPublication=2011
|Logo=GMV
|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 European Geostationary Navigation Overlay Service (EGNOS) improves the open public service offered by the Global Positioning System
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>
(GPS). Currently, EGNOS augments the GPS civilian signal L1, transmitted at frequency 1575.42 MHz. In particular, EGNOS broadcasts differential
corrections and integrity information on the GPS measurements via several geostationary satellites centered on Europe, via an extended network
of ground stations defined in the [[EGNOS Architecture | EGNOS Architecture]].


==EGNOS SIS Interface Characteristics==
==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]]


[[File:GEO FootPrints.JPG| Inmarsat and Artemis EGNOS geostationary broadcast areas  |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">[http://www.essp-sas.eu/service_definition_documents EGNOS Open Service Definition Document]</ref><ref name=" EGNOS SOL SDD">[http://www.essp-sas.eu/service_definition_documents 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).
 
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]] Service Definition Document and the [[EGNOS Safety of Life Service|EGNOS Safety of Life]] Service Definition Document.<ref name=" EGNOS OS SDD">[http://www.essp-sas.eu/service_definition_documents EGNOS Open Service Definition Document]</ref><ref name=" EGNOS SOL SDD">[http://www.essp-sas.eu/service_definition_documents 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).
 
The EGNOS signal is broadcast by two Inmarsat-3 satellites (one positioned east of the Atlantic, and the other above Africa) and by ESA’s  Artemis satellite, which is also above Africa. These three satellites’ orbits are in the equatorial plane, at three different longitudes, with each able to broadcast EGNOS services across the whole ECAC area.<ref name=" EGNOS User Guide for Developers">[http://ec.europa.eu/enterprise/policies/satnav/egnos/files/brochures-leaflets/egnos-user-guide_en.pdf  EGNOS User Guide for Developers]</ref>
 
Unlike the GPS and GLONASS satellites, these three space platforms carry no signal generators. They are fitted with a transponder which does nothing more than relay the signal processed on the ground and sent into space. The elements of the EGNOS satellite infrastructure deployed and their orbital location are detailed in the following table.
 


{| class="wikitable" | align="center"
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.
|-
!align="center" |Satellite || align="center" |  PRN  || align="center" |ID(NMEA) || align="center" |Position
|-
|align="center" |'''ARTEMIS''' || align="center" |  124  || align="center" |37 || align="center" |21.5E
|-
|align="center" |'''INMARSAT AOR-E''' || align="center" |  120  || align="center" |33 || align="center" |15.5W
|-
|align="center" |'''INMARSAT AOR-W''' || align="center" |  126  || align="center" |39 || align="center" |25E
|}


The PRN (Pseudo Random Noise) represents the 1023-bit pseudorandom code employed in the generation of the SIS corresponding to each geostationary satellite. Besides, the footprint of the 3 Geostationary satellites can be observed in the illustration.
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"/>


It is noted that EGNOS does not provide GEO ranging.<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==
==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.  
The EGNOS GEO satellites transmit right-hand circularly polarised (RHCP) signals in  
the L band at 1575.42 MHz (L1). The broadcast signal is a combination of a 1023-bit
PRN navigation code of the GPS family and a 250 bits per second navigation data
message carrying the corrections and integrity data elaborated by the EGNOS ground
segment.  
 
This raw navigation message is ½ convolutional encoded with Forward Error Correcting (FEC) Code resulting in a 500 symbol/second EGNOS data stream.
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>


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 Airbone Equipment</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.
 
The EGNOS SIS is such that, at all unobstructed locations near ground level from
which the satellite is observed at an elevation angle of 5 degrees or higher, the level of
the received RF signal at the output of a 3dBi linearly polarised antenna is within the  
range of –161 dBW to –153 dBW for all antenna orientations orthogonal to the direction  
of propagation. Besides, spurious transmissions will be at least 40dB below unmodulated carrier power over all frequencies.
 
It is intended that future geostationary satellites used for EGNOS replenishment will
broadcast higher minimum signal power levels in order to improve the acquisition and
tracking performance of the user receiver.
 
The most relevant EGNOS signal characteristics are detailed hereafter:<ref name=" RTCA MOPS DO 229"/>


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.
* '''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 centered at the L1 frequency. The bandwidth of the signal transmitted by an EGNOS satellite is at least 2.2MHz.  
* '''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.
* '''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.
* '''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.
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* '''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.
* '''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.


==Navigation Payload Specifications==
==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>


The following tables show key performance parameters of the Inmarsat-3 and Artemis Satellite Navigation Payloads:<ref name=" Inmarsat-3 Satellite Navigation Payload ">Inmarsat-3 Satellite Navigation Payload; G.V. Kinal & O. Razumovsky (Inmarsat, London, United Kingdom)</ref> <ref name=" Artemis Satellite Navigation Payload ">The ESA Artemis Satellite-Navigation Mission: In Orbit Testing and Use in EGNOS; J.Ventura Traverset, P.Y.Dussauze, C.Montefusco & F.Torán (GNSS-1 Project Office, ESA, Toulouse, France); C.Lezy, F.Absolonne, B.Demelenne (ESA Redu Station, Redu, Belgium); A.Bird (Artemis Project, ESA/ESTEC, Noordwijk, The Netherlands)</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.


{| class="wikitable" | align="center"
|-
! || align="center" | Inmarsat-3 || align="center" |  Artemis
|-
| align="center" |  L-Band EIRP at edge of coverage (dBw)  || align="center" |27.5 || align="center" |>27
|-
| align="center" |  BandWidth  || align="center" |2.2MHz || align="center" |4MHz
|-
| align="center" |  Polarisation  || align="center" |RHCP || align="center" |RHCP
|-
| align="center" |  Frequency Stability (over 10s)  || align="center" |4.3x10-11(AOR-E), 1.1x10-11 (AOR-W)) || align="center" |2x10-12
|}
The measured parameters were tested after launch of the specified satellites and, in the case of Artemis, payload specifications were verified from ESA´s Redu ground station in Belgium during the In-Orbit Test (IOT) campaign.
==GPS/SBAS Signal Generators==
A range of signal generators were developed in the GNSS Industry as a means to provide flexible platforms for the testing and signal evaluation.
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.
These generators are easy to integrate on user test environments and their purpose is to evaluate acquisition and tracking algorithms or receiver HW, to design multipath and interference mitigation strategies.
Some of the most representative product manufacturers are Spirent<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> and Novatel.<ref name=" Novatel GUS-Type 1 Signal Generation Product Sheet ">[http://webone.novatel.ca/assets/Documents/Papers/GUSSignalGenerator.pdf    Novatel GUS-Type 1 Signal Generation Product Sheet ]</ref>
==Notes==
<references group="footnotes"/>
<references group="footnotes"/>


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<references/>
<references/>


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

Latest revision as of 13:58, 18 March 2020


EGNOSEGNOS
Title EGNOS Signal Structure
Edited by GMV
Level Basic
Year of Publication 2011
Logo GMV.png

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.[1]

EGNOS SIS Interface Characteristics

Source: EGNOS Service Notice #22 [2]

The EGNOS Signal In Space format is compliant with the ICAO SARPs for SBAS[3] as stated in the EGNOS Open Service Definition Document and the EGNOS Safety of Life Service Definition Document.[4][5] The EGNOS SIS interface characteristics comprise carrier and modulation radio frequency, message structure, protocol and content of the EGNOS message (detailed in the 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 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 ground segment uplink stations.[4]

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).[1]

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). [6]

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.[4] 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:[6]

  • 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.[7]

In addition, there are other flexible platforms useful to generate test signals for development and evaluation of user SBAS receivers.[8] 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

  1. ^ a b EGNOS V3 contract awarded
  2. ^ EGNOS Service Notice #22
  3. ^ 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.
  4. ^ a b c EGNOS Open Service Definition Document
  5. ^ EGNOS Safety of Life Service Definition Document
  6. ^ a b Minimum Operational Performance Standards for Global Positioning System/Wide Area Augmentation System Airborne Equipment (RTCA MOPS 229)
  7. ^ Novatel GUS-Type 1 Signal Generation Product Sheet
  8. ^ Spirent GSS4100 Signal Generator Product Reference Sheet