If you wish to contribute or participate in the discussions about articles you are invited to contact the Editor

GPS Architecture: Difference between revisions

From Navipedia
Jump to navigation Jump to search
mNo edit summary
(First upload)
Line 7: Line 7:
|Logo=GMV
|Logo=GMV
}}
}}
The GPS system is divided into three major segments: Space Segment, Control Segment and User Segment
==The Space Segment==
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 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 GPS architecture is divided into three major segments: a [[GPS Space Segment]] (SS), a [[GPS Ground Segment]] (CS), and a [[GPS User Segment]] (US).


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.
==[[GPS Space Segment|The Space Segment]]==
The main functions of the [[GPS 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.


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 GPS Space Segment is formed by a satellite constellation 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 present configuration allows users to have a simultaneous observation of at least 4 satellites in view worldwide, with an elevation masking angle of 15º.
==[[GPS Ground Segment|The Ground Segment]]==
The [[GPS Ground Segment]] (also referred to as Control Segment) is the responsible for the proper operation of the GPS system.  


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.
The GPS Control Segment is composed by a network of Monitor Stations (MS), a Master Control Station (MCS) and the Ground Antennas (GA).  
GPS uses NAVSTAR satellites manufactured by Rockwell International. Each NAVSTAR satellite is approximately 5 meters wide (with solar panels extended) and weighs approximately 900Kg.


==The Control Segment==
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 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).  
==[[GPS User Segment|The User Segment]]==
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 [[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 [[:Category:Receivers|GNSS Receivers]].
 
==Boundaries Among Segments==
 
[[File:GPS_architecture.png|GPS segments|right|thumb|300px]]
 
The communication boundaries between these three segments are documented in the Interface Control Documents (ICDs):<ref>[http://www.gps.gov/technical/icwg/ GPS Interface Control Documents ICDs</ref>


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.
* IS-GPS-200:<ref name=" IS-GPS-200-E "> Interface Specification IS-GPS-200, Revision E</ref> defines the requirements related to the interface between the Space Segment (SS) of the Global Positioning System (GPS) and the navigation User Segment (US) of the GPS for radio frequency (RF) link 1 (L1) and link 2 (L2).
* IS-GPS-705):<ref name=" IS-GPS-705A "> Interface Specification IS-GPS-705A</ref> defines the requirements related to the interface between the Space Segment (SS) of the Global Positioning System (GPS) and the navigation User Segment (US) of the GPS for radio frequency (RF) link 5 (L5).
* ICD-GPS-870:<ref name=" ICD-GPS-870 "> Interface Specification ICD-GPS-870 </ref> This ICD defines the interfaces between the Operational Control Segment and the GPS users. The files provided by the Control Segment to the users are the Almanacs, Operational Advisories (OAs), Anti-Spoofing (A-S) status, and the Notice Advisory to Navstar Users (NANUs).


Prior to the modernization program, the Monitor Stations network comprised five sites located in:  
[[File:GPS_triad.png|right|thumb|300px]]
# 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:
Besides these interface documents, the following three centers (privately referred as the Big Three or the GPS triad) provide a interface between GPS and any user, civilian or military:<ref>[http://www.pnt.gov/public/docs/2008/idmpublicsummary.pdf U. S. Positioning, Navigation, and Timing Interference Detection and Mitigation Plan Summary]</ref>
# Adelaide (Australia),  
# Buenos Aires (Argentina),  
# Hermitage (UK),  
# Manama (Bahrain),
# Quito (Ecuador) and  
# Washington DC (USA).


Five more stations were added afterwards in 2006:
* '''U.S. Strategic Command GPS Operations Center (GPSOC)''': is  the Department of Defense (DoD) primary point of contact for information regarding status of GPS Precise Positioning Service (PPS) and GPS Standard Positioning Service (SPS). The GPSOC is in charge of responding to inquiries and providing information regarding the GPS constellation and the existence of space segment anomalies or issues that could result in GPS outages worldwide.
# Fairbanks (Alaska),
* '''U.S. Coast Guard (USCG) Navigation Center (NAVCEN)''': is the primary interface to all civil non-aviation users of GPS. It provides capabilities for question or issue resolution regarding GPS anomalies and interference reporting, to support maritime and land users with prioritized approach for safety-of-life applications.
# Osan (South Korea),  
* '''Federal Aviation Administration (FAA) National Operations Control Center (NOCC)''': Responsible for the management and resolution of all aviation reported interference. Due to the safety-of-life considerations, the FAA has well-defined procedures for dealing with the notification and coordination of any interference reports from aviation users, which includes the processing of National Airspace System (NAS) interference reports and specifically, GPS interference reports.
# 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).
==Notes==
<references group="footnotes"/>
==References==
<references/>


==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]].


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

Revision as of 13:55, 31 March 2011


GPSGPS
Title GPS Architecture
Author(s) 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 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 GPS Space Segment is formed by a satellite constellation 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

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

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 (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):[1]

  • IS-GPS-200:[2] defines the requirements related to the interface between the Space Segment (SS) of the Global Positioning System (GPS) and the navigation User Segment (US) of the GPS for radio frequency (RF) link 1 (L1) and link 2 (L2).
  • IS-GPS-705):[3] defines the requirements related to the interface between the Space Segment (SS) of the Global Positioning System (GPS) and the navigation User Segment (US) of the GPS for radio frequency (RF) link 5 (L5).
  • ICD-GPS-870:[4] This ICD defines the interfaces between the Operational Control Segment and the GPS users. The files provided by the Control Segment to the users are the Almanacs, Operational Advisories (OAs), Anti-Spoofing (A-S) status, and the Notice Advisory to Navstar Users (NANUs).
GPS triad.png

Besides these interface documents, the following three centers (privately referred as the Big Three or the GPS triad) provide a interface between GPS and any user, civilian or military:[5]

  • U.S. Strategic Command GPS Operations Center (GPSOC): is the Department of Defense (DoD) primary point of contact for information regarding status of GPS Precise Positioning Service (PPS) and GPS Standard Positioning Service (SPS). The GPSOC is in charge of responding to inquiries and providing information regarding the GPS constellation and the existence of space segment anomalies or issues that could result in GPS outages worldwide.
  • U.S. Coast Guard (USCG) Navigation Center (NAVCEN): is the primary interface to all civil non-aviation users of GPS. It provides capabilities for question or issue resolution regarding GPS anomalies and interference reporting, to support maritime and land users with prioritized approach for safety-of-life applications.
  • Federal Aviation Administration (FAA) National Operations Control Center (NOCC): Responsible for the management and resolution of all aviation reported interference. Due to the safety-of-life considerations, the FAA has well-defined procedures for dealing with the notification and coordination of any interference reports from aviation users, which includes the processing of National Airspace System (NAS) interference reports and specifically, GPS interference reports.


Notes

References

  1. ^ [http://www.gps.gov/technical/icwg/ GPS Interface Control Documents ICDs
  2. ^ Interface Specification IS-GPS-200, Revision E
  3. ^ Interface Specification IS-GPS-705A
  4. ^ Interface Specification ICD-GPS-870
  5. ^ U. S. Positioning, Navigation, and Timing Interference Detection and Mitigation Plan Summary
Retrieved from "https://gssc.esa.int/navipedia/index.php?title=GPS_Architecture&oldid=1847"