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GNSS Performances
| Fundamentals | |
|---|---|
| Title | GNSS Performances |
| Author(s) | GMV |
| Level | Basic |
| Year of Publication | 2011 |
Performance of a positioning system is most usually measured in terms of positioning error (accuracy) and of the portion of the time it can be used for the intended application (availability). However, other performance parameters can become important for some applications. For instance, when a positioning system is used for air or maritime navigation, an unwarned large position error can seriously increase the risk of an accident, possibly causing damage of goods, injuries to people or even death. Such errors can occur without violating the accuracy specification, and this is why the civil aviation community has defined the concept of integrity as a measure of the probability that such hazardous situations can take place. Also, since some flight phases (such as approach and landing) are of special criticality, as well as bounded in duration, it is important that the positioning system remains available without interruptions, very specially during such short periods, but actually all flight phases have certain needs at this respect. That is why the civil aviation community has defined a fourth performance parameter called continuity.
Performance Parameters
The civil aviation community has put the greatest effort in the rationalisation and standardisation of positioning (navigation) performance parameters and requirements, thus specifying the so-called Required Navigation Performance (RNP) that an airborne navigation system must accomplish[1]:
- RNP: A statement of the navigation performance accuracy, integrity, continuity and availability necessary for operations within a defined airspace.
The four parameters on which RNP specification is based are summarised hereafter[2]:
- Accuracy[footnotes 1]: is the degree of conformance between the estimated or measured position and/or velocity of a platform at a given time and its true position or velocity
- Availability: is the portion of time during which the system is to be used for navigation during which reliable navigation information is presented to the crew, autopilot, or other system managing the flight of the aircraft
- Continuity: is the capability of the system to perform its function without unscheduled interruptions during the intended operation
- Integrity: is a measure of the trust which can be placed in the correctness of the information supplied by the total system. Integrity includes the ability of a system to provide timely and valid warnings to the user (alerts) when the system must not be used for the intended operation (or phase of flight)
Notes
- ^ This accuracy definition has been taken from the 2008 US Federal Radionavigation Plan[3]
References
- ^ Report of the Special Communications/Operations Divisional Meeting, ICAO Doc. 9650, November 1995
- ^ Annex 10 (Aeronautical Telecommunications) To The Convention On International Civil Aviation, Volume I – Radio Navigation Aids, International Standards And Recommended Practices (SARPs), ICAO Doc. AN10-1, 6th Edition, July 2006
- ^ Federal Radionavigation Plan, DOT-VNTSC-RITA-08-02/DoD-4650.5, 2008