Quality Control Algorithms on Wide-area Reference Station for WAAS

Changdon Kee, Todd Walter, 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. Because ionosphere/troposphere-free pseudorange and ionospheric time delay outputs from dual-frequency equipped Wide-area Reference Stations (WRSs) are the input of Wide-area Master Station (WMS), the accuracies of the estimated WAAS corrections and the integrity checks at the WMS greatly depend on the quality of the WRS outputs. The WMS also needs to know how confident the WRS outputs are so that it can use them to generate accurate corrections and their confidence values. These corrections and confidence values are passed to WAAS users to compute precise positions and how confident the positions are. Considering the above, WRS is required to generate accurate output and also its confidence value in real time. This paper introduces divergence-free Hatch filter and combines the filter optimally with weighted least square estimation technique to get weighted Hatch filter. The weighted Hatch filter is a very simple and practical filter to generate confidence value and to improve the quality of the WRS output. The paper also introduces a new real- time filter to estimate the rate of ionospheric time delay with an accuracy of better than 0.2mm/sec using Ll and L2 continuous carrier phases and the filter can be used to detect even a half cycle slip and to cycle slip recovery process. The above technique can also be applied to mobile users as well as static users.
Published in:	Proceedings of the 52nd Annual Meeting of The Institute of Navigation (1996) June 19 - 21, 1996 Royal Sonesta Hotel Cambridge, MA
Pages:	487 - 495
Cite this article:	Kee, Changdon, Walter, Todd, Enge, Per, Parkinson, Bradford, "Quality Control Algorithms on Wide-area Reference Station for WAAS," Proceedings of the 52nd Annual Meeting of The Institute of Navigation (1996), Cambridge, MA, June 1996, pp. 487-495.
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