Improved Modeling of GPS Selective Availability

Michael S. Braasch, AnnMarie Fink and Keith Duffus

Abstract:	Selective Availability (SA) represents the dominant error source for stand-alone users of GPS. Even for DGPS, SA mandates the update rate required for a desired level of accuracy in realtime applications. As has been witnessed in the recent literature, the ability to model this error source is crucial to the proper evaluation of GPS-based systems. A variety of SA models have been proposed to date, however, each has its own shortcomings. Most of these models have been based on limited data sets or data which have been corrupted by additional error sources. This paper presents a comprehensive treatment of the problem. The phenomenon of SA is discussed and a technique is presented whereby both clock and orbit components of SA are identifiable. Extensive SA data sets collected from Block II satellites are presented. System Identification theory then is used to derive a robust model of SA from the data. This theory also allows for the statistical analysis of Sk The stationarity of SA over time and across different satellites is analyzed and its impact on the modeling problem is discussed.
Published in:	Proceedings of the 1993 National Technical Meeting of The Institute of Navigation January 20 - 22, 1993 Parc 55 Hotel San Francisco, CA
Pages:	121 - 130
Cite this article:	Braasch, Michael S., Fink, AnnMarie, Duffus, Keith, "Improved Modeling of GPS Selective Availability," Proceedings of the 1993 National Technical Meeting of The Institute of Navigation, San Francisco, CA, January 1993, pp. 121-130.
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