A Flexible RAIM Algorithm

Matthew Powe and John Owen

Abstract:	This paper describes the Receiver Autonomous Integrity Monitoring, RAIM, algorithms used to increase the integrity of GPS receivers' navigation solutions. For the purpose of developing a flexible RAIM algorithm to fulfil the requirements of civil or military systems and not necessarily for aviation, the standard algorithms were found to be inappropriate. They were either inflexible, requiring time consuming simulations to finalise their design, or were flexibly analytic, but only met their design requirements if assumptions are made about the failed satellite's pseudorange error rate. An innovative RAIM algorithm is described, based upon the standard civil algorithms, but which does not require extensive simulation or depend upon error rate assumptions and can therefore be easily adapted to changes in operational requirements. In particular the algorithm can be applied, with equal validity, to the different pseudorange error characteristics of military and civil receivers. The new algorithm performs a more sophisticated assessment of the quality of satellite geometry for satellite failure detection purposes than is the case for the standard civil algorithms. Global RAIM availability percentages, the percentage of time that satellite geometry is of sufficient quality to perform RAIM checking, for the new algorithm are calculated for civil (SPS) and military (PPS) receivers. Availability results for an SPS receiver being used for en-route civil aviation are found to be similar to those calculated for the standard algorithms.
Published in:	Proceedings of the 10th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1997) September 16 - 19, 1997 Kansas City, MO
Pages:	439 - 448
Cite this article:	Powe, Matthew, Owen, John, "A Flexible RAIM Algorithm," Proceedings of the 10th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1997), Kansas City, MO, September 1997, pp. 439-448.
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