The Importance of Accurate UDRE Estimates

Karl Kovach, Larry Huffman

Abstract:	All standardized-format, code-based differential GPS (DGPS) systems are required to provide an estimate of the “user differential range error” (UDRE) associated with each and every differential correction they broadcast to their users. This paper presents the argument that providing accurate UDRE estimates to DGPS users is at least as important as providing accurate differential corrections. This importance is built into the FAA’s Wide Area Augmentation System (WAAS) Specification, however this fact is not yet well appreciated by the average DGPS user. To remedy this situation, this paper reviews certain sections of the WAAS Specification to demonstrate that the UDRE estimates are actually responsible for determining the WAAS user’s availability, continuity, and integrity. The same importance is shown to also apply to local area DGPS systems (particularly those intended for Special Category I [SCAT-I] precision approaches), even though the standards for those systems are largely silent on the subject. This paper includes comparisons of the various ways that accurate UDRE estimates can be generated in both the WAAS and in local area DGPS systems.
Published in:	Proceedings of the 1996 National Technical Meeting of The Institute of Navigation January 22 - 24, 1996 Loews Santa Monica Hotel Santa Monica, CA
Pages:	855 - 869
Cite this article:	Kovach, Karl, Huffman, Larry, "The Importance of Accurate UDRE Estimates," Proceedings of the 1996 National Technical Meeting of The Institute of Navigation, Santa Monica, CA, January 1996, pp. 855-869.
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