WAAS Network Time Performance and Validation Results

Stephen Peck, Cheryl Griffith, Victor Reinhardt, Jonathan Tekawy, William Bertiger, Bruce Haines, Gernot M. R. Winkler

Abstract:	Hughes Aircraft is currently designing the algorithms of the FAA's Wide Area Augmentation System (WAAS). This paper discusses the WAAS network time (WNT) algorithms and their integration into the overall system. The WAAS system is required to provide users with orbit, clock, and ionosphere corrections for single-frequency measurements of the GPS signal. The clock corrections will be made in the WAAS network time (WNT) reference scale. This reference scale is required to track the GPS time scale, while at the same time providing the users with the translation to UTC. Other internal requirements are placed on the WNT bias and frequency jumps from the accuracy demanded in the WAAS fast corrections. The WAAS architecture requires that WNT be computed at multiple WAAS master stations (WMS) using potentially differing sets of measurements from potentially differing sets of receivers and clocks. This design must provide the user a seamless transition when switching from one WMS's WNT realization to another. This paper presents the WNT performance and validation results demonstrating that the WNT design meets the aforementioned specifications, taking into account possible WMS switches. The performance results are based on validation testing using simulations. The simulation models the Allan variance of the receiver clocks, the selective availability effects on the GPS as well as GPS and WAAS clock estimation errors. These results demonstrate the ability of the WNT algorithm to provide seamless transitions and a time reference that agrees with GPS well within the specified 50 nanosecond requirement.
Published in:	Proceedings of the 10th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1997) September 16 - 19, 1997 Kansas City, MO
Pages:	1123 - 1131
Cite this article:	Peck, Stephen, Griffith, Cheryl, Reinhardt, Victor, Tekawy, Jonathan, Bertiger, William, Haines, Bruce, Winkler, Gernot M. R., "WAAS Network Time Performance and Validation Results," Proceedings of the 10th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1997), Kansas City, MO, September 1997, pp. 1123-1131.
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