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

GLONASS General Introduction: Difference between revisions

From Navipedia
Jump to navigation Jump to search
(Dummy information as example)
No edit summary
Line 7: Line 7:
|Logo=GMV
|Logo=GMV
}}
}}
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.
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]]).
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]]
==[[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 Reference Frame| GLONASS Reference Frame]]==
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.
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.
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 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 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.
== [[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]]


Small introduction
Small introduction

Revision as of 15:25, 7 April 2011


GLONASSGLONASS
Title GLONASS General Introduction
Author(s) GMV
Level Basic
Year of Publication 2011
Logo GMV.png


The 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. GPS receivers compute their position in the GPS Reference System using satellite technology and based on triangulation principles (please refer to GNSS positioning). 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[1] lead the US Government to decide to make GPS use free for civilian purposes.[2] Deployment of the GPS system began on 22 February 1978 with the launch of the first Block I Navstar GPS satellite.[3] 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).[4]

GPS block IIR-M satellite

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:[5] L2C for civilian users and a new military signal (M code) in L1 and L2 to provide better jamming resistance than the Y code.[6]

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[5] satellites (May 28th 2010) will be compatible with other GNSS systems.

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. GPS uses the World Geodetic System WGS-84,[7] 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. GPS System Time (GPST) is defined by the 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 Services

GPS provides two levels of service, Standard Positioning Service and the Precise Positioning Service: The Standard Positioning Service (SPS),[8] 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),[9] 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 Architecture

GPS is comprised of three segments: a GPS Space Segment, a GPS Ground Segment, and a GPS User Segment. The main functions of the GPS Space Segment are to transmit radio-navigation signals, and to store and retransmit the navigation message sent by the GPS Ground Segment. The 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 consists on the millions of receivers performing the navigation, timing or other related functions.

GLONASS Performances

The levels of performance that the user can expect from GPS are specified in the Standard Positioning Service Performance Standard,[8] and the Precise Positioning Standard.[9] 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:[10]

  • 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.

GLONASS Future and Evolutions

Aimed at improving the performance for civilian users, the GPS modernization will introduce the following signals:[11]

  • 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.[12]
  • 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.[13][14] 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.

GPS Modernization

Notes

References

  1. ^ Korean Air Lines Flight 007
  2. ^ Global Positioning System on Wikipedia
  3. ^ Block 1 Satellite Information
  4. ^ Federal Agencies
  5. ^ a b Block II Satellite Information
  6. ^ Capt. B.C.Barker et al., Overview of the GPS M Code Signal
  7. ^ J. Sanz Subirana, JM. Juan Zornoza and M. Hernández-Pajares, Global Navigation Satellite Systems: Volume I: Fundamentals and Algorithms
  8. ^ a b Global Positioning System Standard Positioning Service Performance Standard
  9. ^ a b Global Positioning System Precise Positioning Service Performance Standard
  10. ^ The Modernization of GPS: Plans, New Capabilities and the Future Relationship to Galileo, Keith D. McDonald
  11. ^ GPS Modernization Fact Sheet
  12. ^ GPS Modernization and Program Update, Bernie Gruber
  13. ^ GPS OCX Update
  14. ^ OCS contract awarded





Small introduction

This is a new section

GPS block IIR-M satellite

This is an example to cite a reference.[1]

This is an example to cite a reference.[2]

This is an example to cite a reference.[2]


This is a new subsection

Notes

References

  1. ^ EGNOS − The European Geostationary Navigation Overlay System − A Cornerstone of Galileo (ESA SP-1303)
  2. ^ a b EGNOS − The European Geostationary Navigation Overlay System − A Cornerstone of Galileo (ESA SP-1303)
Retrieved from "https://gssc.esa.int/navipedia/index.php?title=GLONASS_General_Introduction&oldid=2431"