A New Position Domain Algorithm to Improve WAAS Availability and Continuity While Maintaining Integrity

Guangwei Mu, Joebob P. Havlicek, and John Fagan

Abstract:	The integrity algorithms are well defined in the Wide Area Augmentation System (WAAS) Minimum Operational Performance Standards (MOPS) [1]. However, our experimental data clearly indicate that the MOPS VPL and HPL algorithms are over-conservative, at least from a practical point of view. As a result, the confidence bounds are sufficiently large to cover the correction error and hence to some extent guarantees the integrity. However, this lack of compactness from the MOPS introduces unnecessary epochs of the system being unavailable. To improve the system performance, the intuitive approach is through the range/correction domain since these factors can be observed, controlled and manipulated to improve the system performance in individual cases. However, we need a better error model and better understanding of the threat model, i.e. we need to know more about the nature of all error sources and the threats the WAAS faces, which is very difficult due to the stochastic natures of these sources, to accomplish this. Therefore, it is unlikely that a range/correction domain solution can be applied to wide range of applications while having significant improvement for the system performance. Besides, it is still subject to the hindrance that the WAAS message structure might need to be changed or adjusted to take advantage of the new development. In this article, we present a new position domain algorithm to improve the MOPS integrity methodology in hopes of improving the overall system performance. The information needed to do this is already in the WAAS messages. Therefore, this new algorithm will not require any change of the existing correction messaging structure. We introduce pseudo-VPL and pseudo-HPL measures in this paper to facilitate the development of the new algorithm, which we will call as the pseudo- VPL algorithm for the vertical part of WAAS improvement. It is based on the currently used MOPS algorithms and improves upon them. The new VPL and HPL algorithms are developed by taking advantage of the WAAS correction error’s stochastic characteristics and a 1-Dimention tracking Kalman filtering. The algorithm has been tested using real static and dynamic data collected by our Enhanced Miniature Advanced GPS Receiver (EMAGR) used in conjunction with the OU flight test program. This methodology shows significant improvement over the standardized MOPS algorithms. It improves the system availability and continuity without penalizing integrity.
Published in:	Proceedings of the 2004 National Technical Meeting of The Institute of Navigation January 26 - 28, 2004 The Catamaran Resort Hotel San Diego, CA
Pages:	145 - 156
Cite this article:	Mu, Guangwei, Havlicek, Joebob P., Fagan, John, "A New Position Domain Algorithm to Improve WAAS Availability and Continuity While Maintaining Integrity," Proceedings of the 2004 National Technical Meeting of The Institute of Navigation, San Diego, CA, January 2004, pp. 145-156.
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