RAIM Availability for Augmented GPS-Based Navigation Systems

William Michalson, Jonathan Bernick, Peter Levin, and Per Enge

Abstract:	As interest in using GPS for sole-means navigation increases, it becomes important to ensure that the system can produce navigation solutions reliably 24 hours a day anywhere in the world. In addition, these solutions must be provided with integrity, meaning that both the navigation solution and a measure of the accuracy of the solution are needed. Providing integrity requires including redundant information to the receiver, which then uses this information to check the consistency of the navigation solution. This need for additional information, however, tends to reduce the availability of integrity monitoring since additional demands for satellite visibility are now placed on the receiver. Currently, the objective is to provide a navigation solution with integrity 99.999% of the time. This paper describes the effect on availability of augmenting the basic GPS system with geostationary satellites or barometric altimeter data. Several proposed augmentations are investigated, including two different augmentations which include geostationary ranging sources (one consisting of DSCS satellites, the other consisting of Inmarsat-3 satellites), augmenting GPS with barometric altimeter data, and augmenting GPS with combinations of these approaches. The availability profile is presented as a topology of RAlM availability as seen over time across CONUS. In this manner, regions of poor availability become readily visible, as do the effects of augmentation. Since RAIM availability is closely related to the geometric criteria used to determine the admissibility of a particular space-time point, several popular admissibility criteria are used in the investigation. These criteria include metrics such as i%LWP~, used by Sturza and Brown, ARP as used by Grover Brown, and the relatively new RPE metric used in the SC-159/WG-5 baseline PDE algorithm.
Published in:	Proceedings of the 7th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1994) September 20 - 23, 1994 Salt Palace Convention Center Salt Lake City, UT
Pages:	587 - 595
Cite this article:	Michalson, William, Bernick, Jonathan, Levin, Peter, Enge, Per, "RAIM Availability for Augmented GPS-Based Navigation Systems," Proceedings of the 7th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1994), Salt Lake City, UT, September 1994, pp. 587-595.
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