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==Combined and Future Services Performances==
==Combined and Future Services Performances==
Combining GPS with other GNSS constellations: GLONASS, GALILEO.


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
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.


* Meet the most demanding user applications.
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.
* 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:
* [[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==

Revision as of 11:14, 3 June 2011


GPSGPS
Title GPS Performances
Author(s) GMV
Level Basic
Year of Publication 2011
Logo GMV.png


The GPS 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 provides two levels of service, 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 frequency and available to all GPS users. The L1 frequency contains a coarse acquisition (C/A) code and a navigation data message.
  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 a navigation data message that is reserved for authorized use by the use of cryptography.

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, 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.


GPS Service Level Perfomances

Standard Positioning Service (SPS) Performances

The Performance standards for SPS Service are:[1]

Service Performances Standards for Standard Positioning Service(SPS)
Standard Positioning Service
Based on Single Frequency
Coverage Global
Availability >99 %
Accuracy (95%) Horizontal: 17 m
Vertical: 37 m
Time Transfer Error < 40 nsec (95%)

Precise Positioning Service (PPS) Performances

The Performance standards for PPS Service are:[2]

Service Performances Standards for Standard Positioning Service(SPS)
Standard Positioning Service
Based on Single Frequency
Coverage Global
Availability >99 %
Accuracy (95%) Horizontal: 17 m
Vertical: 37 m
Time Transfer Error < 40 nsec (95%)

Combined and Future 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.

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.

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
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