Simulation-Based Evaluation of WAAS Performance: Risk and Integrity Factors

Sam Pullen, Per Enge, and Bradford Parkinson

Abstract:	The Wide Area Augmentation System (WAAS) uses an array of monitor stations that combine to compute GPS user corrections over the Continental U.S. Preliminary experiments have concluded that ionospheric spatial decorrelation is the most significant of the WAAS error sources. Recent data on ionospheric errors has been combined into a probability model that describes the likelihood of rare-event ionospheric decorrelations over a range of conditions. Using this model and simpler models for troposphere and other errors, computer simulations of WAAS performance for randomly located users, using the MITRE ionospheric grid algorithm, have been conducted. These simulation studies focused on performance sensitivity to various algorithm parameters and the potential of user-based RAIM algorithms to meet the WAAS availability and integrity requirements. It was found that both standard residual statistics and a new method of projecting spatial decorrelations from the gridpoint estimates show promise in improving overall WAAS performance. Remaining ionospheric uncertainty prevents us from meeting all the requirements, but more detailed experiments will allow us to improve our models and offer better performance.
Published in:	Proceedings of the 7th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1994) September 20 - 23, 1994 Salt Palace Convention Center Salt Lake City, UT
Pages:	975 - 983
Cite this article:	Pullen, Sam, Enge, Per, Parkinson, Bradford, "Simulation-Based Evaluation of WAAS Performance: Risk and Integrity Factors," Proceedings of the 7th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1994), Salt Lake City, UT, September 1994, pp. 975-983.
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