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{{Article Infobox2
{{Article Infobox2
|Category=GLONASS
|Category=GLONASS
|Title={{PAGENAME}}
|Editors=GMV
|Authors=GMV
|Level=Basic
|Level=Basic
|YearOfPublication=2011
|YearOfPublication=2011
|Logo=GMV
|Logo=GMV
|Title={{PAGENAME}}
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[[: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).


The [[:Category:GLONASS|GLONASS]] is a space-based global navigation satellite system ([[GNSS]]) that provides reliable positioning, navigation, and timing services to civilian and military users on a continuous worldwide basis.
==Introduction==
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]]).
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.
GPS was originally developed for the U.S. military, but very early in the experimental phase of GPS 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> lead the US Government to decide to make GPS use free for civilian purposes.<ref>[http://en.wikipedia.org/wiki/Global_Positioning_System Global Positioning System on Wikipedia]</ref>
Deployment of the GPS system began on 22 February 1978 with the launch of the first Block I Navstar GPS satellite.<ref>[ftp://tycho.usno.navy.mil/pub/gps/gpsb1.txt Block 1 Satellite Information]</ref> Initial Operating Capability was declared in December 1993 with 24 operational GPS satellites in orbit. Full Operational Capability was declared in June of 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>[http://www.gps.gov/policy/agencies Federal Agencies]</ref>
 
[[File:GPS_satellite_block_IIR_M.png|GPS block IIR-M satellite|thumb|right|300px]]
 
RELLENAR CON EL ICD DE GLONASS !!!
****************************************************
 
==[[GLONASS Signal Structure|GLONASS Signal Structure]]==
GPS satellites 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">[ftp://tycho.usno.navy.mil/pub/gps/gpsb2.txt 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>[http://www.mitre.org/work/tech_papers/tech_papers_00/betz_overview/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. This signal, available since the launch of the Block IIF<ref name="BlockII-Info"/> satellites (May 28th 2010) will be compatible with other GNSS systems.
 
 
 
 
GLONASS satellites transmit two types of signal: a standard precision (SP) signal and an obfuscated high precision (HP) signal.
 
The signals use similar DSSS encoding and binary phase-shift keying (BPSK) modulation as in GPS signals. All GLONASS satellites transmit the same code as their SP signal, however each transmits on a different frequency using a 15-channel frequency division multiple access (FDMA) technique spanning either side from 1602.0 MHz, known as the L1 band. The center frequency is 1602 MHz + n × 0.5625 MHz, where n is a satellite's frequency channel number (n=−7,−6,−5,...0,...,6, previously n==−7,...0,...,13). Signals are transmitted in a 38° cone, using right-hand circular polarization, at an EIRP between 25 to 27 dBW (316 to 500 watts). Note that the 24 satellite constellation is accommodated with only 15 channels by using identical frequency channels to support antipodal (opposite side of planet in orbit) satellite pairs, as these satellites will never be in view of an earth based user at the same time.
 
The HP 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 than the SP signal.
 
The L2 signals use the same FDMA as the L1 band signals, but transmit straddling 1246 MHz with the center frequency determined by the equation 1246 MHz + n×0.4375 MHz, where n spans the same range as for L1.[33] Other details of the HP signal have not been disclosed.
 
Since 2008, new CDMA signals are being researched for use with GLONASS.
 
Two latest Glonass-K1 satellites to be launched in 2010-2011 will introduce an additional SP CDMA signal for testing purposes, located in the L3 band at 1202.025 MHz.


Glonass-K2 satellites, to be launched in 2013-2015, will feature three additional CDMA signals near the original FDMA frequencies, one obfuscated signal located at 1242 MHz in the L2 band, as well as two signals at 1575.42 MHz in the L1 band; subsequent Glonass-KM satellites to be launched after 2015 will feature an open signal in the L5 band at 1176.45 MHz and even more CDMA signals on existing frequencies.[35
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 Reference Frame| GLONASS Reference Frame]]==
==GLONASS Signal Structure==
Accurate and well-defined Time References and Coordinate Frames are essential in [[GNSS|GNSS]], where positions are computed from signal travel time measurements and provided as a set of coordinates.
[[File:GlonassSignalStructure.JPG|GLONASS Signal Spectrum|400px|thumb|right]]
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.
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">[http://rniikp.ru/en/pages/about/publ/ICD_GLONASS_eng.pdf GLONASS Interface Control Document, Edition 5.1]</ref>
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.
 
 
GLONASS uses a coordinate datum named "PZ-90" (Earth Parameters 1990 – Parametry Zemli 1990), in which the precise location of the North Pole is given as an average of its position from 1900 to 1905. This is in contrast to the GPS's coordinate datum, WGS 84, which uses the location of the North Pole in 1984. As of September 17, 2007 the PZ-90 datum has been updated to differ from WGS 84 by less than 40 cm (16 in) in any given direction.
 
 
==[[GLONASS Services | GLONASS Services]]==
GPS provides two levels of service, Standard Positioning Service and the Precise Positioning Service:
The Standard Positioning Service (SPS),<ref name="SPS-Standard ">[http://pnt.gov/public/docs/2008/spsps2008.pdf Global Positioning System Standard Positioning Service Performance Standard]</ref> is a positioning and timing service provided on GPS L1 frequency and available to all GPS users. The L1 frequency contains a coarse acquisition (C/A) code and a navigation data message.
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) code ranging signal with a navigation data message that is reserved for authorized use by the use of cryptography.
 
 
GLONASS satellites transmit two types of signal: a standard precision (SP) signal and an obfuscated high precision (HP) signal.
 
The HP 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 than the SP signal.
 
Currently, an additional civil reference signal is broadcast in the L2 band with an identical SP code to the L1 band signal. This is available from all satellites in the current constellation, except satellite number 795 which is the last of the inferior original GLONASS design, and one partially inoperable GLONASS-M satellite which is broadcasting only in the L1 band. (see www.glonass-ianc.rsa.ru for daily updates on constellation status.)
 
 
 
==[[GLONASS Architecture | GLONASS Architecture]]==
GPS 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 4 ground antennas which upload the clock and orbit errors, as well as the navigation data message to the GPS satellites.
Finally, the [[GPS User Segment|GPS User Segment]] consists on the millions of receivers performing the navigation, timing or other related functions.  
 
==[[GLONASS Performances| GLONASS Performances]]==
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 Standard.<ref name="PPS-Standard">[http://pnt.gov/public/docs/2007/ppsps2007.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, 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.
 
 
 
At peak efficiency, the SP signal offers horizontal positioning accuracy within 5–10 meters, vertical positioning within 15 meters, a velocity vector measuring within 10 cm/s, and timing within 200 ns, all based on measurements from four first-generation satellites simultaneously;[34] newer satellites such as GLONASS-M improve on this. The more accurate HP signal is available for authorized users, such as the Russian Military, yet unlike the US P(Y) code which is modulated by an encrypting W code, the GLONASS P codes are broadcast in the clear using only 'security through obscurity'. Use of this signal bears risk however as the modulation (and therefore the tracking strategy) of the data bits on the L2P code has recently changed from unmodulated to 250bps burst at random intervals. The GLONASS L1P code is modulated at 50bps without a manchester meander code, and while it carries the same orbital elements as the CA code, it allocates more bits to critical Luni-Solar acceleration parameters and clock correction terms.
 
 
== [[GLONASS Future and Evolutions| GLONASS 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.pnt.gov/public/docs/2006/modernization.pdf GPS Modernization Fact Sheet]</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>[http://scpnt.stanford.edu/pnt/PNT10/presentation_slides/2-PNT_Symposium_Gruber.pdf  GPS Modernization and Program Update, Bernie Gruber]</ref>
* L5 (1176.45 MHz): It will be compatible with other GNSS systems and will transmit at a higher power than current civil GPS signals, and have 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 will be backward compatible with the current civil signal on L1
Moreover, in order to improve the anti-jamming and secure access of the military GPS signals, a new military signal (M-code) will be transmitted in L1 and L2 frequencies.
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>[http://www.pnt.gov/advisory/2010/10/canty.pdf GPS OCX Update]</ref><ref>[http://gps.gov/congress/newsletter/2010/04.pdf OCS contract awarded]</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.
 
[[File:GPS_modernization.png|GPS Modernization|center|frame]]
 
==Notes==
<references group="footnotes"/>
==References==
<references/>


[[Category:GLONASS]]
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.''


Small introduction
[[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.''
==This is a new section==
[[File:GPS_satellite_block_IIR_M.png|GPS block IIR-M satellite|thumb|right|300px]]


This is an example to cite a reference.<ref>[http://www.esa.int/esaMI/ESA_Publications/SEMNMPN0LYE_0.html EGNOS − The European Geostationary Navigation Overlay] System − A Cornerstone of Galileo (ESA SP-1303)</ref>
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.''


This is an example to cite a reference.<ref name="Name ref1"/>
==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.


This is an example to cite a reference.<ref name="Name ref1">[http://www.esa.int/esaMI/ESA_Publications/SEMNMPN0LYE_0.html EGNOS − The European Geostationary Navigation Overlay System − A Cornerstone of Galileo (ESA SP-1303)]</ref>
==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.


===This is a new subsection===
==Notes==
==Notes==
<references group="footnotes"/>
<references group="footnotes"/>
Line 131: Line 65:
<references/>
<references/>


[[Category:GLONASS]]
[[Category:GLONASS|!]]

Latest revision as of 11:08, 22 June 2018


GLONASSGLONASS
Title GLONASS General Introduction
Edited by GMV
Level Basic
Year of Publication 2011
Logo GMV.png

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 System using satellite technology and based on triangulation principles. It is an alternative and complementary to other GNSS systems such as the United States' Global Positioning System (GPS), the Chinese BeiDou navigation system or the planned Galileo positioning system of the European Union (EU).

Introduction

The first Soviet navigation spacecraft “Cyclone” was launched into orbit in 1967.[1] 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 GLONASS were started in 12 October 1982 with the launch of the Kosmos-1413, Kosmos-1414, and Kosmos-1415[1]. 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 [2] 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 [3]. 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 GLONASS navigation system to provide the service free for customers: "Access to civilian navigation signals of global navigation satellite system GLONASS is provided to Russian and foreign consumers free of charge and without limitations".[2]

GLONASS Signal Structure

GLONASS Signal Spectrum

Each 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).[4]

It is important to remark that GLONASS relies on the Frequency Division Multiple Access (FDMA) technique instead of the CDMA one used by other GNSS systems such GPS or GALILEO. Each satellite transmits navigation signals on its own carrier frequency, so that two GLONASS satellites may transmit navigation signals on the same carrier frequency if they are located in antipodal slots of a single orbital plane.[4]

The frequency of transmission of each GLONASS satellite can be derived from the channel number k[5] by applying the following expressions:[4]

  • [math]\displaystyle{ f_{k1} =f_{01} + k\Delta f_1 }[/math], where [math]\displaystyle{ f_{01} =1602 MHz }[/math] and [math]\displaystyle{ \Delta f_1=562.5 KHz }[/math]
  • [math]\displaystyle{ f_{k2} =f_{02} + k\Delta f_2 }[/math], where [math]\displaystyle{ f_{02} =1246 MHz }[/math] and [math]\displaystyle{ \Delta f_2=437.5 KHz }[/math]

The modernization of 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 GNSS positioning). 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.[4]

As specified in the GLONASS Interface Control Document, the 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:[4]

  • 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).[6]
  • 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 GLONASS system:[7]

  • 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

GLONASS is comprised of three segments: a GLONASS Space Segment (SS), a GLONASS Ground Segment (CS), and a GLONASS User Segment (US)[4].

According to the GLONASS Interface Control Document,[4] the 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[8]. 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 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 GLONASS constellation status, correction to the orbital parameters and navigation data uploading.

Finally, GLONASS User Segment consists in the user receivers which compute coordinates, velocity and time from the 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 and GPS Performances are very similar.

GLONASS Future and Evolutions

Glonass K satellite at the CeBIT 2011 Expo in Germany

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.[9]

Evolutions of GLONASS are planned and in place for short, mid and long terms.

Notes

References

  1. ^ a b GLONASS History on Information-analytical centre
  2. ^ a b Announcement of Putin making GLONASS free for customers
  3. ^ GLONASS History on wikipedia
  4. ^ a b c d e f g GLONASS Interface Control Document, Edition 5.1
  5. ^ GLONASS Constellation Status, Information Analytical Centre, Russian Federal Space Agency
  6. ^ Earth Rotation Service (IERS)
  7. ^ J. Sanz Subirana, JM. Juan Zornoza and M. Hernández-Pajares, Global Navigation Satellite Systems: Volume I: Fundamentals and Algorithms
  8. ^ Russian System of Differentional Correction and Monitoring
  9. ^ Innovation: GLONASS, Yuri Urlichich, Valeriy Subbotin, Grigory Stupak, Vyacheslav Dvorkin, Alexander Povalyaev, Sergey Karutin, April 1, 2011, GPS World
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