RAIM of GPS: INS-GPS Integration

P. Misra, M. Pratt and B. Burke

Abstract:	We review an algorithm for receiver autonomous integrity monitoring RAIM) of GPS as a supplemental navigation system. Given the GPS range measurements, one of which may have an unknown amount of bias, the algorithm provides a position estimate and a measure of its quality. The latter, called integrity level of the position estimate, is definedasrif Pmb(qosition error < r} > 0.99999 Position estimates with integrity level I 500 m exceed the current requirements for non- precision approaches. The algorithm has been tested in realtime continuously over several months using actual GPS measurements corrupted randomly to simulate an anomaly in each snapshot. There have been no failures. We have determined that with the 24-satellite GPS constellation (GPS-24), 99% of the users will be able to obtain position estimates which exceed the integrity requirements for non-precision approaches. A 21-satellite constellation (GPS-21) can provide position estimates of this assured quality to 90% of the users. We also investigate the navigation performance achievable by updating an INS using a GPS-derived position estimate, when assured of the quality of the latter. Again, we use the integrity level as the measure of the quality of a position estimate, and present the distribution of waiting times for updating an INS with position estimates of different quality. The results show that with GPS-24, the wait to obtain a position estimate with an integrity level of 500 m is no more than 15 minutes for 99.9% of the users, and no more than 30 minutes for 99.99%. With GPS-21, position estimates of this quality are available to 99% of the users within 15 minutes, and to 99.9% within 30 minutes. The results suggest a number of approaches to implementation, all bringing about a dramatic improvement in navigation accuracy over the oceanic routes achievable immediately.
Published in:	Proceedings of the 6th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1993) September 22 - 24, 1993 Salt Palace Convention Center Salt Lake City, UT
Pages:	545 - 554
Cite this article:	Misra, P., Pratt, M., Burke, B., "RAIM of GPS: INS-GPS Integration," Proceedings of the 6th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1993), Salt Lake City, UT, September 1993, pp. 545-554.
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