Satellite Criticality Concepts for Unavailability and Unreliability of GNSS Satellite Navigation

Curtis A. Shively

Abstract:	This paper derives expressions and approximations for unavailability and unreliability of navigation service using Global Navigation Satellite System (GNSS) satellites. Both unavailability and unreliability are shown to be characterized by a concept known as “critical satellites” - a “critical satellite” is used in every satellite combination with good satellite-user geometry. Numerical results are given showing the levels of unavailability and unreliability associated with the satellite criticality characteristic. In the case of unreliability, these numerical results are compared to existing reliability requirements for precision approaches using the Instrument Landing System (ILS). Insights provided by the critical satellite concept are illustrated via an example of instantaneous unavailability for a Category I (CAT I) precision approach application. This example relates temporal peaks of unavailability to satellite criticality and quantifies the degradation of geometry due to critical satellite failures.
Published in:	Proceedings of the 6th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1993) September 22 - 24, 1993 Salt Palace Convention Center Salt Lake City, UT
Pages:	575 - 589
Cite this article:	Updated citation: Published in NAVIGATION: Journal of the Institute of Navigation
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