LAAS Monitoring For A Most Evil Satellite Failure

Alexander M. Mitelman, Jaewoo Jung, Per K. Enge

Abstract:	The objective of Signal Quality Monitoring (SQM) is to improve integrity of the space segment of Local Area Aug-mentation System (LAAS) by detecting satellite generated GPS signal faults. As seen in the SV19 case, these signal faults are particularly worrisome since pseudorange error may not be common mode between ground and air. This can render the differential correction ineffective, possibly leading to hazardously misleading information (HMI) be-ing supplied to the aircraft. The susceptibility of a differential architecture to such satellite faults is primarily due to the use of non-identical receivers on the ground and in the air. While the correla-tor spacings in aircraft receivers vary widely, most refer-ence stations use narrow correlators to limit the effects of ground-based multipath. For this reason, air and ground correlator spacings are, in general, unequal. This leads to the possibility that a signal could appear to be nominally correct on the ground while generating a significant error at the aircraft. To address the problem, this paper explores the use of one or more additional correlator sample pairs, or monitors, at the reference station to put a finite bound on the worst-case mismatch between ground and air estimates of the code phase. A mathematical model of the reference station is used to derive an explicit worst-case waveform for all pos-sible combinations of air and ground correlator spacings as a function of M, the number of monitors. A simplified fault model using only the nominal GPS signal plus scaled, delayed copies of that signal, is also analyzed.
Published in:	Proceedings of the 1999 National Technical Meeting of The Institute of Navigation January 25 - 27, 1999 Catamaran Resort Hotel San Diego, CA
Pages:	129 - 134
Cite this article:	Mitelman, Alexander M., Jung, Jaewoo, Enge, Per K., "LAAS Monitoring For A Most Evil Satellite Failure," Proceedings of the 1999 National Technical Meeting of The Institute of Navigation, San Diego, CA, January 1999, pp. 129-134.
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