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{{Article Infobox2
{{Article Infobox2
|Category=GALILEO
|Category=GPS
|Title={{PAGENAME}}
|Editors=GMV
|Authors=GMV
|Logo=GMV
|Level=Basic
|Level=Basic
|YearOfPublication=2011
|YearOfPublication=2011
|Logo=GMV
|Title={{PAGENAME}}
}}
}}
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.


Galileo system is a space-based global navigation satellite system (GNSS) that provides reliable positioning, navigation, and timing services to users on a continuous worldwide basis freely available to all.
==Introduction==


The Galileo [[GNSS Performances|performances]] are different for each service. For the [[GALILEO Open Service|Galileo Open Service (OS)]] no specific requirements of [[Integrity|integrity]] are applicable. The [[GNSS Performances|performances]] for horizontal positioning [[Accuracy|accuracy]] at 95% for a dual-frequency receiver are 4 m (8 m for vertical [[Accuracy|accuracy]]), with an [[Availability|availability]] of the service of 99%.  
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.


In the case of the [[GALILEO Safety-of-Life Service|Galileo Safety of Life (SoL)]] and the [[GALILEO Public Regulated Service|Galileo Public Regulated Service (PRS)]], the [[GNSS Performances|performance]] requirements include horizontal and vertical [[Accuracy|accuracy]], [[Integrity|integrity]], [[Continuity|continuity]] and time to alert for different service levels. The [[Availability|availability]] of the service should be 99.5% for both services.  
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.


== Galileo Service Level Perfomances==
== GPS Service Level Performances==
From Galileo Mission High Level Definition, the performances requirements for each service are the following:<ref name="GALHLD"> [http://ec.europa.eu/dgs/energy_transport/galileo/doc/galileo_hld_v3_23_09_02.pdf Galileo Mission High Level Definition], v3, September 2002.</ref>


===Galileo Open Service 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"
{| class="wikitable" align="center"
|+align="bottom" |''Service Performances for [[Galileo Open Service (OS)|Galileo Open Service]]''
|+align="bottom" |''Service Performances Standards for Standard Positioning Service(SPS)''
|-
|-
! rowspan="2" |  
! colspan="2"| GPS Performance Standard Metric
! colspan="2"| Galileo  Open Service (positioning & timing)
! SPS User Performance
|- align="center"
! SPS Signal in Space Performance 
! Single Frequency (SF) 
|- align="center"
! Dual Frequency (DF)
! rowspan="2"| Global Accuracy
|- align="center"
| All-in-View Horizontal 95%
! Coverage
| <100 m
| colspan="2"|         Global
|< 8 m
|- align="center"
|- align="center"  
! rowspan="2" | Accuracy (95%)
| All-in-View Vertical 95%
| Horizontal: 15 m
| <156 m
| Horizontal: 4m
| < 13 m
|- align="center"
|- align="center"
| Vertical: 35 m
! rowspan="2"| Worst Site Accuracy
| Vertical: 8m
| All-in-View Horizontal 95%
|- align="center"
| <100 m
! Availability
|< 15 m
| colspan="2"|         99.8 %
|- align="center"  
|- align="center"
| All-in-View Vertical 95%
! Timing Accuracy wrt UTC/TAI
| <156 m
| < 33 m
|- align="center"
! colspan="2"| User Range Error (URE)
| N/A
| N/A
| 30 ns
| <7.0 m 95% of time
|- align="center"
|- align="center"
! Ionospheric Correction
! colspan="2"| Velocity Accuracy
| Based on SF Model
| N/A
| Based on DF Measurements
| < 0.2 m/sec 95% velocity error
|- align="center"
|- align="center"
! Integrity
| colspan="2"|          No
|}


===Galileo Safety of Life Service Performances===
! colspan="2"| Time Transfer Accuracy
 
| N/A
{| class="wikitable" align="center"
| <30 ns 95% of time
|+align="bottom" |''Service Performances for [[Galileo Safety of Life (SoL)|Galileo Safety of Life Service]]''
|- align="center"
|-
! colspan="2" rowspan="2"| Geometry (PDOP ≤ 6)
! colspan="2" rowspan="2" |
| > 95.86% global
! colspan="2"| Galileo Safety of Life Service
| > 98% global
|- align="center"  
| > 83.9% worst site
| > 88% worst site
|- align="center"   
|- align="center"   
! colspan="2"| Based on Dual Frequency (DF)
! colspan="2"| Constellation Availability
|- align="center"
| N/A
!  colspan="2" | Coverage
| >98% Probability of 21 Healthy Satellites
| colspan="2"|          Global
|- align="center"
! colspan="2" |
! Critical Level
! Non-critical Level
|- align="center"
!  rowspan="2"  colspan="2" | Accuracy (95%)
|  Horizontal: 4 m
|  rowspan="2" | Horizontal: 220 m
|- align="center"
| Vertical: 8 m
|- align="center"
!  rowspan="3" | Integrity (95%)
| Alarm Limit
|  H: 12 m, V: 20 m
| H: 556 m
|- align="center"
| Time-To-Alarm
| 6 seconds
| 10 seconds
|- align="center"
| Integrity Risk
| 3.5x10-7/150s
| 10-7/hour
|- align="center"
!  colspan="2" | Continuity Risk
| 10-5/15s
| 10-4/hour - 10-8/hour
|- align="center"
!  colspan="2" | Certification/Liability
| colspan="2"|          Yes
|- align="center"
!  colspan="2" | Availability of Integrity
| colspan="2"|          99.5 %  
|- align="center"
!  colspan="2" | Availability of accuracy
| colspan="2"|          99.8 %
|- align="center"
|}
|}


===Galileo Public Regulated Service Performances===
===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"
{| class="wikitable" align="center"
|+align="bottom" |''Service Performances for [[Galileo Public Regulated Service (PRS)|Galileo PRS]]''
|+align="bottom" |''Service Performances Standards for Precise Positioning Service (PPS)''
|-
|-
! colspan="2" rowspan="2" |  
! colspan="2"| GPS Performance Standard Metric
! colspan="2" | Galileo Public Regulated Service (PRS)
! 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"   
|- align="center"   
! colspan="2"| Dual Frequency (DF)
! colspan="2"| Geometry (PDOP ≤ 6)
|- align="center"
| >95.7% global
! colspan="2"| Coverage
| >98% global
| Global
|- align="center"
|- align="center"
! colspan="2"| Constellation Availability
! colspan="2" rowspan="2" | Accuracy (95%)
| N/A
| Horizontal: 6.5 m
| >98% Probability of 21 Healthy Satellites
|- align="center"
| Vertical: 12 m
|- align="center"
! colspan="2"| Availability  
| 99.5 %
|- align="center"
! colspan="2"| Timing Accuracy wrt UTC/TAI
| 100 ns
|- align="center"
! colspan="2"| Ionospheric Correction
| Based on DF Measurements
|- align="center"
! rowspan="4" |Integrity
!Computes
|Yes
|- align="center"   
!Alarm Limit
| H:20 m -V:35 m
|- align="center"   
!Time-To-Alarm
| 10 s
|- align="center"   
!Integrity Risk
| 3.5x10e-7/150 s
|- align="center"
! colspan="2"| Continuity Risk
| 10e-5/15 s
|}
|}


===Galileo Commercial Service===
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.
The [[Galileo Commercial Service (CS)|Galileo Commercial Service]] will be a controlled access service operated by Commercial Service Providers, who will make decisions on the offered services: e.g. integrity data, differential corrections for local areas, etc., which will depend on the final characteristics of the other services offered by Galileo.
 
==Segment Performance Drivers==
 
To fulfil the Galileo Services requirements, especially with respect to integrity and continuity, key performance drivers have been defined and flown down to Segment
level, i.e. Space Segment (SSEG), Ground Mission Segment (GMS), Test User Segment (TUS), and Ground Control Segment (GCS).
 
The Orbit Determination & Time Synchronisation (ODTS) performance is also driving the signal performance quality indicator, SISA, which needs to be ensured in all available GMS states. Such ensuring of signal quality directly drives Galileo's integrity services. Furthermore the ground monitoring performance indicator, SISMA, is required for the integrity services, and two GMS states exist that are defined via the related SISMA upper bound performance. The final SSEG and GMS key performance requirements are summarized below and are driving OS as well as SOL service performance. The nominal state is if all  Galileo Sensor Stations (GSS) and 27 Signal in Space (SIS) from the operational satellites are available.<ref>Veit Oehler, Jan M. Krueger, Tanja Beck, Michael Kirchner, Hans L. Trautenberg, Jörg Hahn, Daniel Blonski, [http://www.giove.esa.int/images/userpage/ION_2009_EADS.pdf  “Galileo System Performance Status Report,”] Proceedings of the ION GNSS 2009, Savannah, GA, USA, Sept. 22-25, 2009.</ref>
 
{| class="wikitable" align="center"
|+align="bottom" |''Segment Performances for Galileo''
|- align="center"
!
! Nominal 
! Degraded
! Service
|- align="center"
! ODTS /Ranging Accuracy (1 sigma)
| colspan="2"|          65 cm
| OS
|- align="center"
! GMS Availability of Navigation
| colspan="2"|          99.95 %
| OS
|- align="center"
! SISA
| colspan="2"|          85 cm
| SoL
|- align="center"
! SISMA
| 70 cm
| 130 cm
| SoL
|- align="center"
! GMS Availability of Integrity
| 94.73 %
| 5.23 %
| SoL
|- align="center"
! SSEG State Probability
| 94.09 %
| 5.66 %
| OS,SoL 
|}


Such segment key performances drivers have been independently consolidated through the early GIOVE experimentation activities, which show great consistency with the "designed" performance status.
==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:<ref name="GALHLD"/>


* 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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