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{{Article Infobox2
{{Article Infobox2
|Category=GPS
|Category=GPS
|Title={{PAGENAME}}
|Editors=GMV
|Authors=GMV
|Logo=GMV
|Level=Basic
|Level=Basic
|YearOfPublication=2011
|YearOfPublication=2011
|Logo=GMV
|Title={{PAGENAME}}
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The US Global Positioning System (GPS) provides 24/7 positioning and timing services for worldwide users.
GPS supplies two different service levels, Standard Positioning Service and the Precise Positioning Service:
# The Standard Positioning Service (SPS),<ref name="SPS-Standard ">[https://www.gps.gov/technical/ps/2020-SPS-performance-standard.pdf Global Positioning System Standard Positioning Service Performance Standard]</ref> is a positioning and timing service provided on GPS L1, L2 and L5 frequencies and available to all GPS users. The L1 frequency contains a coarse acquisition (C/A) code and a navigation data message. The L2 frequency contains a CM-code and CL-code signals whereas I5-code and Q5-code signals are transmitted in L5 frequency.
# 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/Y) code ranging signal with an encrypted navigation data message that is reserved for authorized users.
==Introduction==
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 Service Standard.<ref name="PPS-Standard">[http://www.gps.gov/technical/ps/2007-PPS-performance-standard.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, [[Differential GPS|DGPS]], 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.
More advanced techniques, such as [[Real Time Kinematics|Real Time Kinematics]] or [[Precise Point Positioning]], might provide performances in the order of a few centimeters.
== GPS Service Level Performances==
The Performances of each Service are different and they are specified in the Standard Positioning Service Performance Standard, and the Precise Positioning Standard. 
===Standard Positioning Service (SPS) Performances===
The Performance standards for SPS Service based on Single Frequency C/A-Code are:<ref name="SPS-Standard "/>
{| class="wikitable" align="center"
|+align="bottom" |''Service Performances Standards for Standard Positioning Service(SPS)''
|-
! colspan="2"| GPS Performance Standard Metric
! SPS User Performance
! SPS Signal in Space Performance 
|- align="center" 
! rowspan="2"| Global Accuracy
| All-in-View Horizontal 95%
| <100 m
|< 8 m
|- align="center"
| All-in-View Vertical 95%
| <156 m
| < 13 m
|- align="center" 
! rowspan="2"| Worst Site Accuracy
| All-in-View Horizontal 95%
| <100 m
|< 15 m
|- align="center"
| All-in-View Vertical 95%
| <156 m
| < 33 m
|- align="center" 
! colspan="2"| User Range Error (URE)
| N/A
| <7.0 m 95% of time
|- align="center" 
! colspan="2"| Velocity Accuracy
| N/A
| < 0.2 m/sec 95% velocity error
|- align="center" 
! colspan="2"| Time Transfer Accuracy
| N/A
| <30 ns 95% of time
|- align="center" 
! colspan="2" rowspan="2"| Geometry (PDOP ≤ 6)
| > 95.86% global
| > 98% global
|- align="center"
| > 83.9% worst site
| > 88% worst site
|- align="center" 
! colspan="2"| Constellation Availability
| N/A
| >98% Probability of 21 Healthy Satellites
|}
===Precise Positioning Service (PPS) Performances===
The Performance standards for PPS Service based on Dual Frequency P/Y-Code are:<ref name="PPS-Standard "/>
{| class="wikitable" align="center"
|+align="bottom" |''Service Performances Standards for Precise Positioning Service (PPS)''
|-
! colspan="2"| GPS Performance Standard Metric
! SPS User Performance
! SPS Signal in Space Performance 
|- align="center" 
! rowspan="2"| Global Accuracy
| All-in-View Horizontal 95%
| < 36 m
|< 13 m
|- align="center"
| All-in-View Vertical 95%
| < 77 m
| < 22 m
|- align="center" 
! colspan="2"| User Range Error (URE)
| N/A
| <5.9 m 95% of time
|- align="center" 
! colspan="2"| Time Transfer Accuracy
| N/A
| <40 ns 95% of time
|- align="center" 
! colspan="2"| Integrity
| N/A
| < 1x10-5 Probability Over Any Hour
|- align="center" 
! colspan="2"| Geometry (PDOP ≤ 6)
| >95.7% global
| >98% global
|- align="center" 
! colspan="2"| Constellation Availability
| N/A
| >98% Probability of 21 Healthy Satellites
|}
In general, PPS performance standards are in line with SPS ones. Some advantages of PPS Service opposite to the SPS Service are that PPS access to WAGE (Wide Area GPS Enhancements) rapid ephemeris updates and corrections, and the use of dual frequency  to correct the delay suffered by the signal in its transmission through the [[Ionospheric Delay|ionosphere]] in real time, which implies a significant performance improvement. The P/Y code is encrypted to avoid spoofing and the access to the service to unauthorised users.


== GPS Service Level Perfomances==
==Modernized Signals Performances==
Since the beginning of the transmission of the CNAV navigation message, by April 2014, the L2C signal is suffering several improvements. On March 2015 the U.S. Air Force reported that signal performance of CNAV matches or slightly outperforms Legacy performance: average user range error (RMS URE) from 25 February – 3 March 2015 was 0.50 m for Legacy and 0.57 m for Modernized; best week for Modernized signals since the broadcast initiated April 2014 was 0.42 m for 6 – 13 January 2015<ref>[http://gpsworld.com/cnav-performance-matches-or-slightly-outperforms-legacy-signals/ CNAV Performance ‘Matches or Slightly Outperforms’ Legacy Signals], GPS World, March 19, 2015</ref>.


==Combined services performances==
==Combined Services Performances==
Galileo is being designed to be interoperable with other systems and, therefore, it will, in a great many instances, be used as part of a combined service. The identification of combined services is necessary to


* Meet the most demanding user applications.
GPS can be interoperable with other GNSS systems. When combining GPS with other GNSS constellations this enhances positioning performance. This is due to an improvement in [[Availability|availability]], i.e. the number of satellites in view is larger, and geometry.
* Reduce satellite navigation system weaknesses.
* Provide robust solutions for applications requiring system redundancy for safety and/or security reasons.
* Access future GNSS market.
* Enable and expand new market opportunities.


The most obvious systems to be combined with Galileo are the other existing [[GNSS systems description|GNSS systems]], GPS,GLONASS, SBAS and GBAS as they share with Galileo many characteristics that facilitate a combination at user level. By combining Galileo with other GNSS systems, improved performance in the following domains can be expected:
There are other ways to enhance the GPS positioning solution, such as [[GNSS Augmentation]] systems, or [[Differential GNSS|Differential GNSS]] techniques, that are explained in more detail in the corresponding articles. With DGNSS the [[Accuracy|accuracy]] is improved to the order of 1 m, and the GNSS Augmentation systems assure [[Integrity|integrity]].
* [[Availability]]: Using as an example Galileo in combination with GPS and SBAS systems, the number of operational satellites will be in the region of 60. In normal urban environments this would result in an increased availability for 4 satellites from 40% to more than 90%.
* Position [[Accuracy]]: Allied to an increased availability in restricted environments (urban) is a better geometry of spacecraft or enhanced positioning performance.
* [[Integrity]]: GNSS based integrity systems and techniques, such as [[SBAS General Introduction|SBAS]], [[RAIM|RAIM]] and [[GBAS]], would benefit from the addition of new constellations, including Galileo, in terms of lower achievable protection levels and/or integrity risk.
* Redundancy: By combining services from separate and fully independent systems full redundancy can be achieved. This is particularly important for Safety of Life applications that require full system backup.


==References==
==References==
<references/>
<references/>


[[Category:GPS|Performances]]
[[Category:GPS]]
[[Category:GPS Performance]]

Latest revision as of 12:38, 4 December 2020


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

The US Global Positioning System (GPS) provides 24/7 positioning and timing services for worldwide users.

GPS supplies two different service levels, Standard Positioning Service and the Precise Positioning Service:

  1. The Standard Positioning Service (SPS),[1] is a positioning and timing service provided on GPS L1, L2 and L5 frequencies and available to all GPS users. The L1 frequency contains a coarse acquisition (C/A) code and a navigation data message. The L2 frequency contains a CM-code and CL-code signals whereas I5-code and Q5-code signals are transmitted in L5 frequency.
  2. The Precise Positioning Service (PPS),[2] is a highly accurate military positioning, velocity and timing service broadcasted at the GPS L1 and L2 frequencies. Both frequencies contain a precision (P/Y) code ranging signal with an encrypted navigation data message that is reserved for authorized users.


Introduction

The levels of performance that the user can expect from GPS are specified in the Standard Positioning Service Performance Standard,[1] and the Precise Positioning Service Standard.[2] 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:[3]

  • C/A-code receivers ~ 5 -10 m.
  • P/Y-code receivers ~ 2 -9 m

In case of using GPS in a differential mode, DGPS, 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.

More advanced techniques, such as Real Time Kinematics or Precise Point Positioning, might provide performances in the order of a few centimeters.

GPS Service Level Performances

The Performances of each Service are different and they are specified in the Standard Positioning Service Performance Standard, and the Precise Positioning Standard.

Standard Positioning Service (SPS) Performances

The Performance standards for SPS Service based on Single Frequency C/A-Code are:[1]

Service Performances Standards for Standard Positioning Service(SPS)
GPS Performance Standard Metric SPS User Performance SPS Signal in Space Performance
Global Accuracy All-in-View Horizontal 95% <100 m < 8 m
All-in-View Vertical 95% <156 m < 13 m
Worst Site Accuracy All-in-View Horizontal 95% <100 m < 15 m
All-in-View Vertical 95% <156 m < 33 m
User Range Error (URE) N/A <7.0 m 95% of time
Velocity Accuracy N/A < 0.2 m/sec 95% velocity error
Time Transfer Accuracy N/A <30 ns 95% of time
Geometry (PDOP ≤ 6) > 95.86% global > 98% global
> 83.9% worst site > 88% worst site
Constellation Availability N/A >98% Probability of 21 Healthy Satellites

Precise Positioning Service (PPS) Performances

The Performance standards for PPS Service based on Dual Frequency P/Y-Code are:[2]

Service Performances Standards for Precise Positioning Service (PPS)
GPS Performance Standard Metric SPS User Performance SPS Signal in Space Performance
Global Accuracy All-in-View Horizontal 95% < 36 m < 13 m
All-in-View Vertical 95% < 77 m < 22 m
User Range Error (URE) N/A <5.9 m 95% of time
Time Transfer Accuracy N/A <40 ns 95% of time
Integrity N/A < 1x10-5 Probability Over Any Hour
Geometry (PDOP ≤ 6) >95.7% global >98% global
Constellation Availability N/A >98% Probability of 21 Healthy Satellites

In general, PPS performance standards are in line with SPS ones. Some advantages of PPS Service opposite to the SPS Service are that PPS access to WAGE (Wide Area GPS Enhancements) rapid ephemeris updates and corrections, and the use of dual frequency to correct the delay suffered by the signal in its transmission through the ionosphere in real time, which implies a significant performance improvement. The P/Y code is encrypted to avoid spoofing and the access to the service to unauthorised users.

Modernized Signals Performances

Since the beginning of the transmission of the CNAV navigation message, by April 2014, the L2C signal is suffering several improvements. On March 2015 the U.S. Air Force reported that signal performance of CNAV matches or slightly outperforms Legacy performance: average user range error (RMS URE) from 25 February – 3 March 2015 was 0.50 m for Legacy and 0.57 m for Modernized; best week for Modernized signals since the broadcast initiated April 2014 was 0.42 m for 6 – 13 January 2015[4].

Combined Services Performances

GPS can be interoperable with other GNSS systems. When combining GPS with other GNSS constellations this enhances positioning performance. This is due to an improvement in availability, i.e. the number of satellites in view is larger, and geometry.

There are other ways to enhance the GPS positioning solution, such as GNSS Augmentation systems, or Differential GNSS techniques, that are explained in more detail in the corresponding articles. With DGNSS the accuracy is improved to the order of 1 m, and the GNSS Augmentation systems assure integrity.

References

  1. ^ a b c Global Positioning System Standard Positioning Service Performance Standard
  2. ^ a b c Global Positioning System Precise Positioning Service Performance Standard
  3. ^ The Modernization of GPS: Plans, New Capabilities and the Future Relationship to Galileo, Keith D. McDonald
  4. ^ CNAV Performance ‘Matches or Slightly Outperforms’ Legacy Signals, GPS World, March 19, 2015
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