Comparison of Full Vector and Common View WAAS Algorithms

Changdon Kee, Todd Walter, Yi-Chung Chao, Yeou-Jyh Tsai, Jennifer Evans, Andy Barrows, Eric Abbot, David Powell, Per Enge, and Bradford Parkinson

Abstract:	The Wide Area Augmentation System (WAAS) is being rapidly developed for operational use in 1997. At that time, it will be a supplemental navigation aid for all phases of flight down to Category I precision approach. Eventually, it will be a primary navigation aid. The WAAS system reduces the overall cost and the operational cost of the system dramatically and increases the system reliability and integrity compared to a Local Area Differential GPS (LADGPS). The WAAS system calculates and transmits a vector of error corrections (the three-dimensional ephemeris errors, satellite clock offsets including Selective Availability (SA), and ionospheric time delays) to the users via a geostationary satellite. The WAAS correction message will follow a signal and data format specified by RTCA Special Committee 159. The Full Vector WAAS (FVWAAS) algorithm solves the WRS’s clock, three-dimensional ephemeris errors, and satellite clock offsets for all satellites at the same time. The Common View WAAS (CVWAAS) algorithm uses a well-known time transfer method to synchronize time for all Wide Area Reference Stations (WRSs) and solves the three-dimensional ephemeris errors and satellite clock offsets for each satellite. Stanford University installed three WRSs in the Western United States and has been conducting independent flight tests of WAAS since the Summer of 1994. All three WRSs are at least 400 km from the location of the flight tests. This paper includes the results from the Stanford WAAS static and flight tests and compares the two different WAAS algorithms, FVWAAS and CVWAAS algorithm. In these algorithms the WAAS error corrections are generated as soon as the satellite is visible from the WAAS network. This paper also includes an improvement on the existing grid ionosphere estimation algorithm by considering ionospheric time delay measurement noise and introduces a weighted least-square solution in WAAS user position computation.
Published in:	Proceedings of the 51st Annual Meeting of The Institute of Navigation (1995) June 5 - 7, 1995 Antlers Doubletree Hotel Colorado Springs, CO
Pages:	491 - 499
Cite this article:	Kee, Changdon, Walter, Todd, Chao, Yi-Chung, Tsai, Yeou-Jyh, Evans, Jennifer, Barrows, Andy, Abbot, Eric, Powell, David, Enge, Per, Parkinson, Bradford, "Comparison of Full Vector and Common View WAAS Algorithms," Proceedings of the 51st Annual Meeting of The Institute of Navigation (1995), Colorado Springs, CO, June 1995, pp. 491-499.
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