WAAS Measurement Processing, Reducing the Effects of Multipath

Karl Shallberg, Peter Shloss, Eric Altshuler and Lu Tahmazyan

Abstract:	The accuracy, availability and integrity of the Wide Area Augmentation System (WAAS) are of significant concern because of this systems intended use in commercial aviation applications. The first level of service provided by WAAS will be modest, but upgrades that will provide significant improvements in service have been defined for both ground and space segments. One particular area of study has been the WAAS Reference Station (WRS) measurement quality. WRS measurement quality has a significant influence on integrity processing and ultimately system availability. The dominant noise term for pseudorange measurements in WAAS is multipath. WAAS currently makes extensive use of carrier phase leveling using dual frequency measurements to estimate and remove multipath from the pseudorange measurements. Techniques have also been devised to provide the proper statistical representation of the remaining error in the multipath-corrected measurements. This paper discusses the treatment of WRS multipath error in the WAAS design. The key aspect of this work was the development of a function that met the strict Gaussian overbound properties required by the WAAS integrity monitors. This paper also provides an overview of the WRS multipath environment, the multipath estimation algorithm for GPS measurements, system performance and overbound validation methodology, and finally, some comments on future improvements in WAAS multipath processing.
Published in:	Proceedings of the 14th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2001) September 11 - 14, 2001 Salt Palace Convention Center Salt Lake City, UT
Pages:	2334 - 2340
Cite this article:	Shallberg, Karl, Shloss, Peter, Altshuler, Eric, Tahmazyan, Lu, "WAAS Measurement Processing, Reducing the Effects of Multipath," Proceedings of the 14th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2001), Salt Lake City, UT, September 2001, pp. 2334-2340.
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