Alternate Algorithms for Steering to Make GPS Time

Paul A. Koppang, Demetrios Matsakis and Mihran Miranian

Abstract:	The current GPS Time bang-bang steering algorithm was chosen to provide minimal control perturbation given the constraint that steering is achieved by accelerating time (frequency drift), as opposed to direct adjustment of frequency. This constraint was necessary because satellite clock corrections are updated independently of each other, and typically only daily and when they are sufficiently close to an upload site. One consequence of this is that GPS Time has differed from that of the USNO Master Clock (UTC(USNO)) by about 6 ns RMS in the past year, and in a month-long event beginning late December 1994, it deviated by up to 250 ns. The planned GPS architecture improvements of satellite crosslinks and improved ground clocks justify consideration of switching the steering strategy to one involving direct frequency adjustments to GPS Time. We present an analysis that uses Linear Quadratic Gaussian (LQG) theory to optimize a steering strategy in which frequency is adjusted in proportion to the weighted offset of GPS Time in time and frequency.
Published in:	Proceedings of the 13th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2000) September 19 - 22, 2000 Salt Palace Convention Center Salt Lake City, UT
Pages:	933 - 936
Cite this article:	Koppang, Paul A., Matsakis, Demetrios, Miranian, Mihran, "Alternate Algorithms for Steering to Make GPS Time," Proceedings of the 13th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2000), Salt Lake City, UT, September 2000, pp. 933-936.
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