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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 GPS system is divided into three major segments: Space Segment, Control Segment and User Segment
 


==The Space Segment==
==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 main functions of the Space Segment are to generate and transmit code and carrier phase 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 Ground Segment==
The [[GPS Ground Segment]] (also referred to as Control Segment) is the responsible for the proper operation of the GPS system.  


The GPS Space Segments are formed by satellite constellations with enough satellites to ensure that the users will have, at least, 4 simultaneous satellites in view from any point at the earth surface at any time.
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).


In the case of GPS, the constellation consists of at least 24 satellites, arranged in 6 orbital planes, with an inclination of 55 degrees in relation to the equator with an additional three satellites in orbit as redundant backup.
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).


Orbits are nearly circular, with eccentricity less than 0:02, a semi-major axis of 26 560 km, i.e. an altitude of 20 200 km, and a period of 12 sidereal hours (11 h 58m 2 s), repeating the geometry each sidereal day. This means that each GPS satellite orbits the Earth twice each day. There is a spare satellite slot in each orbital plane, being the system capable of supporting a constellation of up to 30 satellites on orbit.  
==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]].
The present configuration allows users to have a simultaneous observation of at least 4 satellites in view worldwide, with an elevation masking angle of 15º.


Highly accurate atomic clocks are installed on these satellites, operating at a fundamental frequency of 10.23MHz each. With the help of these clocks, signals are generated from the satellite, to be broadcast to the Earth.
==Boundaries Among Segments==
GPS uses NAVSTAR satellites manufactured by Rockwell International. Each NAVSTAR satellite is approximately 5 meters wide (with solar panels extended) and weighs approximately 900Kg.
[[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>[http://www.gps.gov/technical/icwg/ GPS Interface Control Documents ICDs]</ref>
# IS-GPS-200:<ref name=" IS-GPS-200-E ">[https://www.gps.gov/technical/icwg/IS-GPS-200L.pdf  Interface Specification IS-GPS-200, Revision L]</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://www.gps.gov/technical/icwg/IS-GPS-705G.pdf Interface Specification IS-GPS-705, Revision G]</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://www.gps.gov/technical/icwg/IS-GPS-800G.pdf Interface Specification IS-GPS-800, Revision G]</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://www.gps.gov/technical/icwg/ICD-GPS-240C.pdf Interface Specification IS-GPS-240, Revision C]</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://www.gps.gov/technical/icwg/ICD-GPS-870E.pdf Interface Specification ICD-GPS-870, Revision E]</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.


==The Control Segment==
== 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>
 
The Control Segment (also referred to as Ground 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.
*In the case of GPS, the Control Segment is also responsible for Selective Availability
*(S/A) activation in signal transmission.
 
 
The GPS Control Segment is composed by a network of Monitor Stations (MS), a Master Control Station (MCS) and the Ground Antennas (GA).  
The Master Control Station, located at Colorado Springs, is the core of the Control segment. It is responsible for operating the system, providing command, control and maintenance services to the space segment.
 
The Monitor Stations are distributed around the world. They are 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.
 
Prior to the modernization program, the Monitor Stations network comprised five sites located in Hawaii, Colorado Springs (Colorado, US), Ascension Island (South Atlantic), Diego Garcia (Indian Ocean), and Kwajalein (North Pacific). Cape Canaveral (Florida, US) was incorporated in 2001.
 
The modernization program added six new stations to the network in 2005: Adelaide (Australia), Buenos Aires (Argentina), Hermitage (UK), Manama (Bahrain), Quito (Ecuador) and Washington DC (USA). Five more stations were added afterwards in 2006: Fairbanks (Alaska), Osan (South Korea), Papeete (Tahiti), Pretoria (South Africa) and Wellington (New Zealand). With this configuration, each satellite is seen from at least three monitor stations, which allows computing more precise orbits and ephemeris data, therefore improving system accuracy.
 
The Ground Antennas uplink data to the satellites via S-band radio signals. These data includes ephemerides and clock correction information transmitted within the Navigation Message, as well as command telemetry from the MCS. Every satellite can be uploaded 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, and Kwajalein).
 
 
==The User Segment==
 


The 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 [[:Category:Receivers|GNSS Receivers]].
==Notes==
<references group="footnotes"/>
==References==
<references/>


[[Category:GPS]]
[[Category:GPS|Architecture]]

Latest revision as of 07:48, 30 November 2020


GPSGPS
Title GPS Architecture
Edited by GMV
Level Basic
Year of Publication 2011
Logo GMV.png

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.[1]

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: [2]

  • 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.

Boundaries Among Segments

GPS segments

The communication boundaries between these three segments are documented in the Interface Control Documents (ICDs):[3]

  1. IS-GPS-200:[4] 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).
  2. IS-GPS-705):[5] defines the requirements related to the interface between the GPS space and user segments of the GPS for radio frequency (RF) link 5 (L5).
  3. IS-GPS-800:[6] Defines the characteristics of the L1 Civil (L1C) signal transmitted from GPS satellites to navigation receivers on radio frequency link 1 (L1).
  4. IS-GPS-240::[7] 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.
  5. ICD-GPS-870:[8] 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.[9]

Notes

References

  1. ^ GPS Space Segment information in GPS official website
  2. ^ GPS Ground Segment in GPS official website
  3. ^ GPS Interface Control Documents ICDs
  4. ^ Interface Specification IS-GPS-200, Revision L
  5. ^ Interface Specification IS-GPS-705, Revision G
  6. ^ Interface Specification IS-GPS-800, Revision G
  7. ^ Interface Specification IS-GPS-240, Revision C
  8. ^ Interface Specification ICD-GPS-870, Revision E
  9. ^ Civil GPS Service Interface Committee in GPS official website
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