Geo Uplink Subsystem (GUS) Clock Steering Algorithms Performance and Validation Results

M.S. Grewal, W. Brown, R. Lucy, P.Hsu

Abstract:	Raytheon Systems Company is currently developing the FAA’s Wide Area Augmentation System (WAAS). This paper will discuss the GUS clock steering algorithms, performance and validation results. The WAAS Wide Area Master Station (WMS) calculates WAAS Network Time (WNT) and clock parameters (offset and drift) for each satellite. The GUS clock is an independent free running clock. However, the GUS clock must track WNT (GPS time) to enable accurate ranging off the GEO signal-in-space. Therefore, a clock steering algorithm is necessary. The GUS clock steering algorithms reside in the WAAS Message Processor (WMP). The WAAS Type 9 messages (GEO Navigation Message), which are provided by the WMS, are used as inputs to the GUS WMP. The GUS WMP calculates clock adjustments. Based upon these clock adjustments, the frequency standard can be made to speed up or slow down the GUS clock. The GUS cesium frequency standard is controlled through very small frequency control signals so that the normal operation of the code and frequency control loops of the downlink signals will not be disturbed. Simulation and field results for the primary GUS are discussed in the paper. The typical results are that the system settles to a tracking error of ± 5 nsec, after hours with corrections occurring every 15 minutes.
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:	853 - 859
Cite this article:	Grewal, M.S., Brown, W., Lucy, R., P.Hsu,, "Geo Uplink Subsystem (GUS) Clock Steering Algorithms Performance and Validation Results," Proceedings of the 1999 National Technical Meeting of The Institute of Navigation, San Diego, CA, January 1999, pp. 853-859.
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