A New Step Detector Algorithm For GPS/SBAS Receiver

Masato Kawai, Shigeki Hara, Osamu Arai

Abstract:	According to the WAAS MOPS (RTCA/DO-229B)[1], GPS/SBAS receiver must have a capability of pseudorange step detection. It detects step error greater than 700 meters on any satellite used in position solution so that it improves an integrity and an accuracy. The MOPS introduces step detector algorithm as an example in Appendix I. This algorithm brings us to the following questions: (1) Does the screen test meet the false detection probability (PFD)? (2) If the loss-of-lock time is 9 seconds, the screen test threshold becomes 883.8 m. Can it detect 700 m step with 883.8 m threshold? Then we came up with a new approach of step detection for GPS/SBAS receiver. This paper introduces a new algorithm for Step Detector. The new algorithm is simple and straight-forward. It consists of two blocks. One is for the detection of a change in navigation data. And the other is for the detection of a sudden change of the code phase. The former block calculates satellite position by using the current ephemeris and the previous one. Then it takes a difference of the satellite position between them so that it can judge whether a step has occurred or not. The latter block estimates the current pseudorange by using the previous delta range. And it takes a difference between the estimated pseudorange and the observed pseudorange for a step error judgment. All judgments use proper thresholds to meet the false detection probability requirement in the MOPS. The detail algorithms and the results of the test are presented in this paper.
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:	2571 - 2578
Cite this article:	Kawai, Masato, Hara, Shigeki, Arai, Osamu, "A New Step Detector Algorithm For GPS/SBAS Receiver," 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. 2571-2578.
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