Editing GLONASS (section)

== System description ==
{{Comparison satellite navigation orbits}}

GLONASS is a global navigation satellite system, providing real time position and velocity determination for military and civilian users. The satellites are located in middle circular orbit at {{cvt|19100|km}} altitude with a 64.8° inclination and an orbital period of 11 hours and 16 minutes (every 17 revolutions, done in 8 sidereal days, [[Satellite revisit period|a satellite passes over the same location]]<ref>{{Cite web |title=GNSS Knowledge - GLONASS - Borealis Precision - Industry Leading Representative |url=https://www.gnss.ca/gnss/1361-glonass |access-date=2023-10-30 |website=www.gnss.ca}}</ref>).<ref name="ato_glonass"/><ref name="federal_targeted_program_2002">{{cite web|url=http://www.dtic.mil/cgi-bin/GetTRDoc?Location=U2&doc=GetTRDoc.pdf&AD=ADA484380|title=The Global Navigation System GLONASS: Development and Usage in the 21st Century|publisher=34th Annual Precise Time and Time Interval (PTTI) Meeting|year=2002|access-date=21 February 2011|archive-date=1 December 2012|archive-url=https://web.archive.org/web/20121201201715/http://www.dtic.mil/cgi-bin/GetTRDoc?Location=U2&doc=GetTRDoc.pdf&AD=ADA484380|url-status=dead}}</ref> GLONASS's orbit makes it especially suited for usage in high latitudes (north or south), where getting a [[GPS]] signal can be problematic.<ref name="harvey_military">{{cite book|last=Harvey|first=Brian|title=The Rebirth of the Russian Space Program|publisher=Springer|location=Germany|year=2007|edition=1st|chapter=Military programs|isbn=978-0-387-71354-0}}</ref><ref name="moskvitch">{{cite news|url=http://news.bbc.co.uk/2/hi/8595704.stm|title=Glonass: Has Russia's sat-nav system come of age?|work=BBC News|date=2010-04-02|first=Katia|last=Moskvitch|access-date=22 February 2011|archive-date=13 September 2012|archive-url=https://archive.today/20120913/http://news.bbc.co.uk/2/hi/8595704.stm|url-status=live}}</ref>

The constellation operates in three orbital planes, with eight evenly spaced satellites on each.<ref name="federal_targeted_program_2002"/> A fully operational constellation with global coverage consists of 24 satellites, while 18 satellites are necessary for covering the territory of Russia. To get a position fix the receiver must be in the range of at least four satellites.<ref name="ato_glonass"/>

=== Signal ===
{{anchor|Signals}}

==== FDMA ====
[[File:Glonass-receiver.jpg|thumb|290px|A combined GLONASS/GPS receiver, ruggedised for the Russian military, 2003]]
[[File:GLONASS GPS Personal Radio Beacon.jpg|thumb|290px|A combined GLONASS/GPS Personal Radio Beacon]]

GLONASS satellites transmit two types of signals: open standard-precision signal L1OF/L2OF, and [[obfuscated]] high-precision signal L1SF/L2SF.

The signals use similar [[Direct-sequence spread spectrum|DSSS]] encoding and [[Phase-shift keying|binary phase-shift keying]] (BPSK) modulation as in GPS signals. All GLONASS satellites transmit the same code as their standard-precision signal; however each transmits on a different frequency using a 15-channel [[frequency-division multiple access]] (FDMA) technique spanning either side from 1602.0 [[Hertz|MHz]], known as the L1 band. The center frequency is 1602&nbsp;MHz + ''n'' × 0.5625&nbsp;MHz, where ''n'' is a satellite's frequency channel number (''n''=−6,...,0,...,6, previously ''n''=0,...,13). Signals are transmitted in a 38° cone, using right-hand [[circular polarization]], at an [[Effective radiated power|EIRP]] between 25 and 27 [[Decibel watt|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 point|antipodal]] (opposite side of planet in orbit) satellite pairs, as these satellites are never both in view of an Earth-based user at the same time.

The L2 band signals use the same FDMA as the L1 band signals, but transmit straddling 1246&nbsp;MHz with the center frequency 1246&nbsp;MHz + ''n'' × 0.4375&nbsp;MHz, where ''n'' spans the same range as for L1.<ref name="glonass_xmtr">GLONASS transmitter specs</ref> In the original GLONASS design, only obfuscated high-precision signal was broadcast in the L2 band, but starting with GLONASS-M, an additional civil reference signal L2OF is broadcast with an identical standard-precision code to the L1OF signal.

The open standard-precision signal is generated with [[XOR gate|modulo-2 addition]] (XOR) of 511&nbsp;kbit/s pseudo-random ranging code, 50 bit/s navigation message, and an auxiliary 100&nbsp;Hz [[Meander (mathematics)|meander]] sequence ([[Manchester code]]), all generated using a single time/frequency oscillator. The pseudo-random code is generated with a 9-stage shift register operating with a period of 1 [[millisecond]]s.

The navigational message is modulated at 50 bits per second. The superframe of the open signal is 7500 bits long and consists of 5 frames of 30 seconds, taking 150 seconds (2.5 minutes) to transmit the continuous message. Each frame is 1500 bits long and consists of 15 strings of 100 bits (2 seconds for each string), with 85 bits (1.7 seconds) for data and check-sum bits, and 15 bits (0.3 seconds) for time mark. Strings 1-4 provide immediate data for the transmitting satellite, and are repeated every frame; the data include [[ephemeris]], clock and frequency offsets, and satellite status. Strings 5-15 provide non-immediate data (i.e. [[almanac]]) for each satellite in the constellation, with frames I-IV each describing five satellites, and frame V describing remaining four satellites.

The ephemerides are updated every 30 minutes using data from the Ground Control segment; they use [[ECEF|Earth Centred Earth Fixed]] (ECEF) Cartesian coordinates in position and velocity, and include lunisolar acceleration parameters. The almanac uses modified [[orbital elements]] (Keplerian elements) and is updated daily.

The more accurate high-precision signal is available for authorized users, such as the Russian military, yet unlike the United States P(Y) code, which is modulated by an encrypting W code, the GLONASS restricted-use codes are broadcast in the clear using only ''[[security through obscurity]]''. The details of the high-precision signal have not been disclosed. The modulation (and therefore the tracking strategy) of the data bits on the L2SF code has recently changed from unmodulated to 250 bit/s burst at random intervals. The L1SF code is modulated by the navigation data at 50 bit/s without a [[Manchester code|Manchester meander code]].

The high-precision signal is broadcast in phase quadrature with the standard-precision signal, effectively sharing the same carrier wave, but with a ten-times-higher bandwidth than the open signal. The message format of the high-precision signal remains unpublished, although attempts at reverse-engineering indicate that the superframe is composed of 72 frames, each containing 5 strings of 100 bits and taking 10 seconds to transmit, with total length of 36 000 bits or 720 seconds (12 minutes) for the whole navigational message. The additional data are seemingly allocated to critical [[Lunisolar calendar|Lunisolar]] acceleration parameters and clock correction terms.

===== Accuracy =====
At peak efficiency, the standard-precision signal offers horizontal positioning accuracy within 5–10 metres, vertical positioning within {{cvt|15|m}}, a velocity vector measuring within {{cvt|100|mm/s}}, and timing within 200 [[nanosecond]]s, all based on measurements from four first-generation satellites simultaneously;<ref name="miller_2000">"A Review of GLONASS" Miller, 2000</ref> newer satellites such as GLONASS-M improve on this.

GLONASS uses a coordinate [[Geodetic datum|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 1990 to 1995. This is in contrast to the GPS's coordinate datum, [[World Geodetic System|WGS 84]], which uses the location of the North Pole in 1984. As of 17 September 2007, the PZ-90 datum has been updated to version PZ-90.02 which differ from WGS 84 by less than {{cvt|400|mm}} in any given direction. Since 31 December 2013, version PZ-90.11 is being broadcast, which is aligned to the [[International Terrestrial Reference System and Frame]] 2008 at epoch 2011.0 at the centimetre level, but ideally a conversion to ITRF2008 should be done.<ref name=icg8>[http://www.oosa.unvienna.org/pdf/icg/2013/icg-8/wgD/D3_3_2.pdf National Reference Systems of the Russian Federation used in GLONASS.] {{Webarchive|url=https://web.archive.org/web/20140714182933/http://www.oosa.unvienna.org/pdf/icg/2013/icg-8/wgD/D3_3_2.pdf |date=14 July 2014 }} V. Vdovin and M. Vinogradova (TSNIImash), 8th ICG meeting, Dubai, November 2013</ref><ref>{{cite web|url=http://www.glonass-iac.ru/en/content/news/?ELEMENT_ID=721|title=The transition to using the terrestrial geocentric coordinate system "Parametry Zemli 1990" (PZ-90.11) in operating the GLObal NAvigation Satellite System (GLONASS) has been implemented|website=glonass-iac.ru|access-date=2 September 2015|archive-date=7 September 2015|archive-url=https://web.archive.org/web/20150907014714/https://www.glonass-iac.ru/en/content/news/?ELEMENT_ID=721|url-status=dead}}</ref>

==== CDMA ====
Since 2008, new [[Code-division multiple access|CDMA]] signals are being researched for use with GLONASS.<ref name=CDMA>{{cite magazine|url=http://www.insidegnss.com/node/648|title=Russia Approves CDMA Signals for GLONASS, Discussing Common Signal Design|magazine=Inside GNSS|access-date=2010-12-30|archive-url=https://web.archive.org/web/20180313062644/http://www.insidegnss.com/node/648|archive-date=13 March 2018 |url-status=dead}}</ref><ref name=CDMA_report_2007>[http://www.navcen.uscg.gov/pdf/cgsicMeetings/47/%5B21%5D%20GLONASS%20CGSIC%20September%2024%20Fort%20Worth.pdf GLONASS Status and Progress] {{webarchive |url=https://web.archive.org/web/20110614023018/http://www.navcen.uscg.gov/pdf/cgsicMeetings/47/%5B21%5D%20GLONASS%20CGSIC%20September%2024%20Fort%20Worth.pdf|date=14 June 2011}}, S.G.Revnivykh, 47th CGSIC Meeting, 2007. "L1CR and L5R CDMA interoperable with GPS and Galileo"</ref><ref name=CDMA_report_2011>[http://www.unoosa.org/pdf/icg/2010/ICG5/18october/03.pdf GLONASS Status and Development] {{Webarchive|url=https://web.archive.org/web/20130921060649/http://www.unoosa.org/pdf/icg/2010/ICG5/18october/03.pdf |date=21 September 2013 }}, G.Stupak, 5th ICG Meeting</ref><ref name="GNSS2">[http://www.insidegnss.com/node/2487 Russia's First GLONASS-K In Orbit, CDMA Signals Coming] {{Webarchive |url=https://web.archive.org/web/20110307214035/http://www.insidegnss.com/node/2487|date=7 March 2011}} ''[[Inside GNSS]]'' (2011-02-26) Retrieved on 6 October 2011</ref><ref name=CDMA_2011_CGSIG>[https://www.gps.gov/cgsic/meetings/2011/revnivykh.pdf GLONASS Status and Modernization] {{Webarchive|url=https://web.archive.org/web/20191125030536/https://www.gps.gov/cgsic/meetings/2011/revnivykh.pdf |date=25 November 2019 }} Ekaterina Oleynik, Sergey Revnivykh, 51st CGSIG Meeting, September 2011</ref><ref name=CDMA_2011_ICG>[http://www.oosa.unvienna.org/pdf/icg/2011/icg-6/3.pdf GLONASS Status and Modernization] {{Webarchive|url=https://web.archive.org/web/20120515092734/http://www.oosa.unvienna.org/pdf/icg/2011/icg-6/3.pdf |date=15 May 2012 }} Sergey Revnivykh, 6th ICG Meeting, September 2011</ref><ref name=CDMA_2012_ICG>[http://www.unoosa.org/pdf/icg/2012/icg-7/3-1.pdf GLONASS Status and Modernization] {{Webarchive|url=https://web.archive.org/web/20130921060753/http://www.unoosa.org/pdf/icg/2012/icg-7/3-1.pdf |date=21 September 2013 }}, Sergey Revnivykh, 7th ICG Meeting, November 2012</ref><ref name=IGNSS_2013>[http://glonass-iac.ru/aboutIAC/GLONASS_IGNSS-2013_Mirgorodskaya.pdf GLONASS Government Policy, Status and Modernization Plans] {{Webarchive|url=https://web.archive.org/web/20140102194619/http://glonass-iac.ru/aboutIAC/GLONASS_IGNSS-2013_Mirgorodskaya.pdf |date=2 January 2014 }}, Tatiana Mirgorodskaya, IGNSS-2013, 16 July 2013</ref><ref name="ICG_2016"/>

The interface control documents for GLONASS CDMA signals was published in August 2016.<ref name=glonass_icd>[http://russianspacesystems.ru/bussines/navigation/glonass/interfeysnyy-kontrolnyy-dokument/ Russian Space Systems JSC - GLONASS Interface Control Documents] {{Webarchive|url=https://web.archive.org/web/20161022092226/http://russianspacesystems.ru/bussines/navigation/glonass/interfeysnyy-kontrolnyy-dokument/ |date=22 October 2016 }} (in Russian)</ref>

According to GLONASS developers, there will be three open and two restricted CDMA signals. The open signal L3OC is centered at 1202.025&nbsp;MHz and uses BPSK(10) modulation for both data and pilot channels; the ranging code transmits at 10.23 million [[Chip (CDMA)|chips]] per second, modulated onto the carrier frequency using QPSK with in-phase data and quadrature pilot. The data is error-coded with 5-bit [[Barker code]] and the pilot with 10-bit [[Neuman-Hofman code|Neuman-Hoffman code]].<ref>{{cite web|url=http://gpsworld.com/glonass-modernization-12232/|title=GLONASS Modernization|publisher=GPS World|access-date=2 September 2015|date=2 November 2011|archive-url=https://web.archive.org/web/20151117032222/http://gpsworld.com/glonass-modernization-12232/|archive-date=17 November 2015|url-status=dead}}</ref><ref>{{cite web |url=http://www.insidegnss.com/auto/julyaug11-Dumas.pdf |archive-url=https://web.archive.org/web/20140711133448/http://insidegnss.com/auto/julyaug11-Dumas.pdf |archive-date=2014-07-11 |url-status=live|title=Data|date=2011|website=insidegnss.com}}</ref>

Open L1OC and restricted L1SC signals are centered at 1600.995&nbsp;MHz, and open L2OC and restricted L2SC signals are centered at 1248.06&nbsp;MHz, overlapping with GLONASS FDMA signals. Open signals L1OC and L2OC use [[time-division multiplexing]] to transmit pilot and data signals, with BPSK(1) modulation for data and BOC(1,1) modulation for pilot; wide-band restricted signals L1SC and L2SC use BOC (5, 2.5) modulation for both data and pilot, transmitted in quadrature phase to the open signals; this places peak signal strength away from the center frequency of narrow-band open signals.<ref name=CDMA_2012_ICG/><ref name=GPSWorld_Nov_2011>[http://www.gpsworld.com/glonass-modernization-12232/ GLONASS Modernization] {{Webarchive|url=https://web.archive.org/web/20130921060700/http://gpsworld.com/glonass-modernization-12232/ |date=21 September 2013 }}, Yuri Urlichich, Valery Subbotin, Grigory Stupak, Vyacheslav Dvorkin, Alexander Povalyaev, Sergey Karutin, and Rudolf Bakitko, Russian Space Systems, GPS World, November 2011</ref>

[[Phase-shift keying|Binary phase-shift keying]] (BPSK) is used by standard GPS and GLONASS signals. [[Binary offset carrier modulation|Binary offset carrier]] (BOC) is the modulation used by [[Galileo (satellite navigation)|Galileo]], [[modernized GPS]], and [[BeiDou|BeiDou-2]].

The navigational message of CDMA signals is transmitted as a sequence of text strings. The message has variable size - each pseudo-frame usually includes six strings and contains [[ephemerides]] for the current satellite (string types 10, 11, and 12 in a sequence) and part of the almanac for three satellites (three strings of type 20). To transmit the full almanac for all current 24 satellites, a superframe of 8 pseudo-frames is required. In the future, the superframe will be expanded to 10 pseudo-frames of data to cover full 30 satellites.<ref name=GPSWorld_Apr_2011/>

The message can also contain [[Earth's rotation]] parameters, [[ionosphere]] models, long-term orbit parameters for GLONASS satellites, and [[International Cospas-Sarsat Programme|COSPAS-SARSAT]] messages. The system time marker is transmitted with each string; [[Leap second|UTC leap second]] correction is achieved by shortening or lengthening (zero-padding) the final string of the day by one second, with abnormal strings being discarded by the receiver.<ref name=GPSWorld_Apr_2011>[http://www.gpsworld.com/innovation-glonass-11405/ GLONASS: Developing Strategies for the Future] {{Webarchive|url=https://web.archive.org/web/20130921060741/http://gpsworld.com/innovation-glonass-11405/ |date=21 September 2013 }}, Yuri Urlichich, Valeriy Subbotin, Grigory Stupak, Vyacheslav Dvorkin, Alexander Povalyaev, and Sergey Karutin. GPS World, November 2011</ref>

The strings have a version tag to facilitate [[forward compatibility]]: future upgrades to the message format will not break older equipment, which will continue to work by ignoring new data (as long as the constellation still transmits old string types), but up-to-date equipment will be able to use additional information from newer satellites.<ref name=GPSWorld_Nov_2013>[http://gpsworld.com/new-structure-for-glonass-nav-message/ New Structure for GLONASS Nav Message] {{Webarchive|url=https://web.archive.org/web/20131212115824/http://gpsworld.com/new-structure-for-glonass-nav-message/|date=12 December 2013}}, Alexander Povalyaev, GPS World, 2 November 2013</ref>

The navigational message of the L3OC signal is transmitted at 100 bit/s, with each string of symbols taking 3 seconds (300 bits). A pseudo-frame of 6 strings takes 18 seconds (1800 bits) to transmit. A superframe of 8 pseudo-frames is 14,400 bits long and takes 144 seconds (2 minutes 24 seconds) to transmit the full almanac.

The navigational message of the L1OC signal is transmitted at 100 bit/s. The string is 250 bits long and takes 2.5 seconds to transmit. A pseudo-frame is 1500 bits (15 seconds) long, and a superframe is 12,000 bits or 120 seconds (2 minutes).

L2OC signal does not transmit any navigational message, only the pseudo-range codes:
<div style="overflow:auto;">
{| style="font-size: 90%;" class="wikitable"
|+ <span style="font-size: 110%">Roadmap of GLONASS modernization</span>
! rowspan="2" | Satellite series
! rowspan="2" | Launches
! rowspan="2" | Current status
! rowspan="2" | Clock error
! colspan="2" style="background:#bfbaed;"| FDMA signals
! colspan="3" style="background:#99df99;"| CDMA signals
! colspan="3" style="background:#fefe80;"| Interoperability CDMA signals
|-
! style="background:#bfbaed;"| 1602 + n×0.5625&nbsp;MHz
! style="background:#bfbaed;"| 1246 + n×0.4375&nbsp;MHz
! style="background:#99df99;"| 1600.995&nbsp;MHz
! style="background:#99df99;"| 1248.06&nbsp;MHz
! style="background:#99df99;"| 1202.025&nbsp;MHz
! style="background:#fefe80;"| 1575.42&nbsp;MHz
! style="background:#fefe80;"| 1207.14&nbsp;MHz
! style="background:#fefe80;"| 1176.45&nbsp;MHz
|- style="text-align:center;"
| [[GLONASS (satellite)|GLONASS]]
| 1982–2005
| Out of service
| 5{{e|−13}}
| L1OF, L1SF
| L2SF
|
|
|
|
|
|
|- style="text-align:center;"
| [[GLONASS-M]]
| 2003–2022
| In service
| 1{{e|−13}}
| L1OF, L1SF
| L2OF, L2SF
| -
| -
| L3OC <sup>‡</sup>
|
|
|
|- style="text-align:center;"
| [[GLONASS-K]]
| 2011–
| In service
| 5{{e|−14}}...1{{e|-13}}
| L1OF, L1SF
| L2OF, L2SF
| -
| -
| L3OC
|
|
|
|- style="text-align:center;"
| [[GLONASS-K2]]
| 2023–
| Testing
| 5{{e|-15}}...5{{e|−14}}
| L1OF, L1SF
| L2OF, L2SF
| L1OC, L1SC
| L2OC, L2SC
| L3OC
|
|
|
|- style="text-align:center;"
| GLONASS-V
| 2025–
| Design phase
| 
| -
| -
| L1OC, L1SC
| L2OC, L2SC
| L3OC, L3SVI
|
|
|
|- style="text-align:center;"
| GLONASS-KМ
| 2030–
| Research phase
|
| L1OF, L1SF
| L2OF, L2SF
| L1OC, L1SC
| L2OC, L2SC
| L3OC, L3SVI
| L1OCM
| L3OCM
| L5OCM
|-
| colspan="12" | "O": open signal (standard precision), "S": obfuscated signal (high precision); "F":[[FDMA]], "С":[[CDMA]]; n=−7,−6,−5,...,6<br/>
<sup>‡</sup>Glonass-M spacecraft produced since 2014 include L3OC signal
|}</div>

[[Kosmos 2471|Glonass-K1]] test satellite launched in 2011 introduced L3OC signal. Glonass-M satellites produced since 2014 (s/n 755+) will also transmit L3OC signal for testing purposes.

Enhanced Glonass-K1 and [[GLONASS-K2|Glonass-K2]] satellites, to be launched from 2023, will feature a full suite of modernized CDMA signals in the existing L1 and L2 bands, which includes L1SC, L1OC, L2SC, and L2OC, as well as the L3OC signal. Glonass-K2 series should gradually replace existing satellites starting from 2023, when Glonass-M launches will cease.<ref name="ICG_2016">[http://www.unoosa.org/pdf/icg/2016/icg11/01.pdf GLONASS Program Update] {{Webarchive|url=https://web.archive.org/web/20161220060310/http://www.unoosa.org/pdf/icg/2016/icg11/01.pdf |date=20 December 2016 }}, Ivan Revnivykh, Roscosmos, 11th ICG Meeting, November 2016</ref><ref name="testoyedov-2015"/>

Glonass-KM satellites will be launched by 2025. Additional open signals are being studied for these satellites, based on frequencies and formats used by existing GPS, Galileo, and [[BeiDou|Beidou/COMPASS]] signals:

* open signal L1OCM using BOC(1,1) modulation centered at 1575.42&nbsp;MHz, similar to [[GPS signals#L1C|modernized GPS signal L1C]], Galileo signal E1, and Beidou/COMPASS signal B1C;
* open signal L5OCM using BPSK(10) modulation centered at 1176.45&nbsp;MHz, similar to the GPS [[GPS signals#L5, Safety of Life|"Safety of Life" (L5)]], Galileo signal E5a, and Beidou/COMPASS signal B2a;<ref name=CDMA_2010_insideGNSS>{{cite magazine|url=http://www.insidegnss.com/node/1997|title=Russia to Put 8 CDMA Signals on 4 GLONASS Frequencies|magazine=Inside GNSS|date=2010-03-17|access-date=2010-12-30|archive-url=https://web.archive.org/web/20101205054554/http://insidegnss.com/node/1997|archive-date=5 December 2010|url-status=dead}}</ref>
* open signal L3OCM using BPSK(10) modulation centered at 1207.14&nbsp;MHz, similar to Galileo signal E5b and Beidou/COMPASS signal B2b.<ref name=CDMA_report_2011/>
Such an arrangement will allow easier and cheaper implementation of multi-standard [[Satellite navigation|GNSS]] receivers.

With the introduction of CDMA signals, the constellation will be expanded to 30 active satellites by 2025; this may require eventual deprecation of FDMA signals.<ref>{{cite web |url=http://www.gpsworld.com/gnss-system/glonass/news/glonass-update-delves-constellation-details-10499|title=GLONASS Update Delves into Constellation Details|publisher=GPS World|access-date=2010-12-30|url-status=dead|archive-url=https://web.archive.org/web/20110101144902/http://www.gpsworld.com/gnss-system/glonass/news/glonass-update-delves-constellation-details-10499|archive-date=1 January 2011}}</ref> The new satellites will be deployed into three additional planes, bringing the total to six planes from the current three—aided by [[System for Differential Correction and Monitoring]] ([[MacAdam ellipse|SDCM]]), which is a [[GNSS augmentation|GNSS augmentation system]] based on a network of ground-based control stations and communication satellites [[Luch 5A]] and [[Luch 5B]].<ref>{{cite web |url=https://www.gpsworld.com/gnss-systemnewsglonass-modernization-maybe-six-planes-probably-more-satellites-12490/|title=GLONASS Modernization: Maybe Six Planes, Probably More Satellites|publisher=GPS World |date=10 January 2012|access-date=24 December 2018|archive-url=https://web.archive.org/web/20181102235300/http://gpsworld.com/gnss-systemnewsglonass-modernization-maybe-six-planes-probably-more-satellites-12490/|archive-date=2 November 2018|url-status=dead}}</ref><ref name=SDCM_2012>[http://www.unoosa.org/pdf/icg/2012/icg-7/3-2.pdf SDCM status and plans] {{Webarchive|url=https://web.archive.org/web/20140405044651/http://www.unoosa.org/pdf/icg/2012/icg-7/3-2.pdf |date=5 April 2014 }}, Grigory Stupak, 7th ICG Meeting, November 2012</ref> GLONASS-KM satellites will also use new L3SVI open signal to broadcast Precise Point Positioning (PPP) to deliver GLONASS High Accuracy Services.<ref name=ICG_Nepal_2025>{{cite web|url= https://home.csis.u-tokyo.ac.jp/~dinesh/GNSS_Train_files/202501/PresentationMaterials/02_GLONASS.pdf|title=GLONASS Status and Plans of Development|publisher=Roscomsos|website=ICG Programme on GNSS Applications|date=January 28, 2025|access-date=2025-04-09}}</ref>

Six additional [[GLONASS-K#GLONASS-V|Glonass-V]] satellites, using [[Tundra orbit]] in three orbital planes, will be launched starting in 2025;<ref name="tsr-20221219" /> this regional high-orbit segment will offer increased regional availability and 25% improvement in precision over [[Eastern Hemisphere]], similar to Japanese [[Quasi-Zenith Satellite System|QZSS]] system and [[BeiDou|Beidou-1]].<ref name=GPSWorld_GlonassV>{{cite web |url=https://www.gpsworld.com/directions-2019-high-orbit-glonass-and-cdma-signal/|title=Directions 2019: High-orbit GLONASS and CDMA signal|date=12 December 2018|access-date=22 December 2018|archive-url=https://web.archive.org/web/20181222173732/https://www.gpsworld.com/directions-2019-high-orbit-glonass-and-cdma-signal/|archive-date=22 December 2018|url-status=dead}}</ref> The new satellites will form two ground traces with inclination of 64.8°, eccentricity of 0.072, period of 23.9 hours, and ascending node longitude of 60° and 120°. Glonass-V vehicles are based on Glonass-K platform and will broadcast new CDMA signals only.<ref name=GPSWorld_GlonassV/> Previously [[Molniya orbit]], [[geosynchronous orbit]], or [[inclined orbit]] were also under consideration for the regional segment.<ref name=CDMA_report_2011/><ref name=GPSWorld_Apr_2011/>

Roscosmos also plans to launch up to 240 small size satellites on the [[low Earth orbit]] (LEO) to improve signal availability and interfecence; LEO satellites will have a limited lifespan of 5 years to allow a faster pace of replenishment.<ref name=ICG_Nepal_2025/>

=== Navigational message ===
==== L1OC ====
{| class="wikitable"
|+ Full-length string for L1OC navigational message
|-
!colspan="2"| Field !! Size, bits !! Description
|-
|Timecode || СМВ || 12 || Constant bit sequence 0101 1111 0001 (5F1h)
|-
|String type || Тип || 6 || Type of the navigational message
|-
|Satellite ID || j || 6 ||  System ID number of the satellite (1 to 63; 0 is reserved until FDMA signal switch-off)
|-
|Satellite state || Г<sup>j</sup>|| 1 ||  This satellite is:<br/>0 — healthy,<br/>1 — in error state
|-
|Data reliability|| l<sup>j</sup>|| 1 || Transmitted navigational messages are:<br/>0 — valid,<br/>1 — unreliable
|-
|Ground control callback || П1 || 4 ||colspan=2| (Reserved for system use)
|-
|Orientation mode|| П2 || 1 || Satellite orientation mode is:<br/>0 — Sun sensor control,<br/>1 — executing predictive thrust or mode transition
|-
|UTC correction || КР || 2 || On the last day of the current quarter, at 00:00 (24:00), a UTC leap second is:<br/>0 — not expected,<br/>1 — expected with positive value,<br/>2 — unknown,<br/>3 — expected with negative value
|-
|Execute correction || А || 1 || After the end of the current string, UTC correction is:<br/>0 — not expected,<br/>1 — expected
|-
|Satellite time || ОМВ || 16 || Onboard time of the day in 2 seconds intervals (0 to 43199)
|-
|Information || || 184 || Content of the information field is defined by string type
|-
|CRC || ЦК || 16 || Cyclic redundancy code
|-
|colspan="2"| Total || 250
|}

==== L3OC ====
{| class="wikitable"
|+ Full-length string for L3OC navigation message
|-
!colspan="2"| Field !! Size, bits !! Description
|-
|Timecode || СМВ || 20 || Constant bit sequence 0000 0100 1001 0100 1110 (0494Eh)
|-
|String type || Тип || 6 || Type of the navigational message
|-
|Satellite time || ОМВ || 15 ||  Onboard time of the day in 3 seconds intervals (0 to 28799)
|-
|Satellite ID || j || 6 ||rowspan="7"| The same as in L1OC signal
|-
|Satellite state|| Г<sup>j</sup> || 1
|-
|Data reliability|| l<sup>j</sup> || 1
|-
|Ground control callback || П1 ||4
|-
|Orientation mode|| П2 | 222
|-
|UTC correction  || КР || 2
|-
|Execute correction || А || 1
|-
|Information || || 219 || Content of the information field is defined by string type
|-
|CRC ||ЦК || 24 || Cyclic redundancy code
|-
|colspan="2"| Total || 300
|}

==== Common properties of open CDMA signals====
{| class="wikitable"
|+ String types for navigational signals
|-
!Type!! Content of the information field
|-
|0 || (Reserved for system use)
|-
|1 || Short string for the negative leap second
|-
|2 || Long string for the positive leap second
|-
|10, 11, 12 || Real-time information (ephemerides and time-frequency offsets).<br/>Transmitted as a packet of three strings in sequence
|-
|16 || Satellite orientation parameters for the predictive thrust maneuver
|-
|20 || Almanac
|-
|25 || Earth rotation parameters, ionosphere models, and time scale model for the difference between UTC(SU) and [[International Atomic Time|TAI]]
|-
|31, 32 || Parameters of long-term movement model
|-
|50 || Cospas-Sarsat service message — L1OC signal only
|-
|60 || Text message
|}

{| class="wikitable"
|+ Information field of a string type 20 (almanac) for the orbit type 0.<ref group="nb">Navigational message field j (satellite ID) references the satellite for the transmitted almanac (j<sub>A</sub>)</ref>
|-
!colspan="2"| Field !! Size, bits !! Weight of the low bit || Description
|-
|Orbit type || ТО || 2 || 1 || 0 — circular orbit with 19100&nbsp;km altitude <ref group="nb">The set of almanac parameters depends on the orbit type. Satellites with geosynchronous, medium-Earth, and high-elliptical orbits could be employed in the future.</ref>
|-
|Satellite number || N<sub>S</sub> || 6 || 1 || Total number of satellites transmitting CDMA signals (1 to 63) which are referenced to in the almanac.
|-
|Almanac age || E<sub>A</sub> || 6 || 1 || Number of full days passed since the last almanac update.
|-
|Current day || N<sub>A</sub> || 11 || 1 ||  Day number (1 to 1461) within a four-year interval starting on 1 January of the last leap year <ref group="nb">In a departure from the Gregorian calendar, all years exactly divisible by 100 (i.e. 2100 and so on) are treated as leap years</ref> according to [[Moscow decree time]].
|-
|Signal status || PC<sub>A</sub> || 5 || 1 || [[Bit field]] encoding types of CDMA signals transmitted by the satellite.<br/>Three highest bits correspond to signals L1, L2 and L3:<br/>0 — transmitted,<br/>1 — not transmitted
|-
|Satellite type|| PC<sub>A</sub> || 3 || 1 || Satellite model and the set of transmitted CDMA signals:<br/>0 — Glonass-M (L3 signal),<br/>1 — Glonass-K1 (L3 signal),<br/>2 — Glonass-K1 (L2 and L3 signals),<br/>3 — Glonass-K2 (L1, L2, and L3 signals)
|-
|Time correction|| τ<sub>A</sub> || 14 || 2<sup>−20</sup> || Rough correction from onboard time scale to the GLONASS time scale ({{val|±7.8e-3}} с).
|-
|Ascension|| λ<sub>A</sub> || 21 || 2<sup>−20</sup> || Longitude of the satellite's first orbital node (±1 half-cycles).
|-
|Ascension time|| t<sub>λ<sub>A</sub></sub> || 21 || 2<sup>−5</sup> || Time of the day when the satellite is crossing its first orbital node (0 to 44100 s).
|-
|Inclination|| Δi<sub>A</sub> || 15 || 2<sup>−20</sup> || Adjustments to nominal inclination (64,8°) of the satellite orbit at the moment of ascension (±0.0156 half-cycles).
|-
|Eccentricity|| ε<sub>A</sub> || 15 || 2<sup>−20</sup> || Eccentricity of the satellite orbit at the ascension time (0 to 0.03).
|-
|Perigee|| ω<sub>A</sub> || 16 || 2<sup>−15</sup> || Argument to satellite's perigee at the ascension time (±1 half-cycles).
|-
|Period|| ΔT<sub>A</sub> || 19 || 2<sup>−9</sup> || Adjustments to the satellite's nominal draconic orbital period (40544 s) at the moment of ascension (±512 s).
|-
|Period change|| ΔṪ<sub>A</sub> || 7 || 2<sup>−14</sup> || Speed of change of the draconic orbital period at the moment of ascension ({{val|±3.9e-3}} s/orbit).
|-
|colspan="2" rowspan="2" | (Reserved) || L1OC: 23 || colspan="3" rowspan="2" | -
|-
|L3OC: 58
|}
{{reflist|group=nb}}