USDRAIM: An Innovative Approach to Increasing RAIM Availability

Jonathan Bemick and William Michalson

Abstract:	In order to use GPS as a sole-means navigation aid for non-precision approach it is necessary to insure that the system can produce navigation solutions, with integrity, reliably 24 hours a day. In this context, integrity refers to the ability of user equipment to determine if a computed navigation solution is accurate to within 555m radially, the RTCA tolerance for non-precision approach. Unfortunately, all previous RAIM methods only provide such protection when 5 or more satellites are in view. Should ground masking or satellite failure reduce the number of usable satellites to less than 5, no integrity checking is available. Underdetermined Systems RAIM (UDSRAIM) allows solutions with integrity to be obtained when 4 satellites are in view. Three methods are detailed: The first two obtain integrity information by assuming one coordinate of the user position 4-vector to be constant, creating redundancy with only 4 satellites in view; the third works by using the pseudoinverse for underdetermined matrices to find 3-dimensional positions in space, with clock bias, using subgroups of 3 satellites.
Published in:	Proceedings of the 8th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1995) September 12 - 15, 1995 Palm Springs, CA
Pages:	1965 - 1973
Cite this article:	Bemick, Jonathan, Michalson, William, "USDRAIM: An Innovative Approach to Increasing RAIM Availability," Proceedings of the 8th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1995), Palm Springs, CA, September 1995, pp. 1965-1973.
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