Coarse Correction of Selected Availability Affects Using Markov Models in an Extended Kalman Filter

William J. Negast and Randall N. Paschal

Abstract:	An Extended Kalman filter is often used to es- timate errors contained in the navigation solu- tion of an inertial navigation system (INS). GPS pseudorange measurements can be provided to the Kalman filter to update the filter’s estimates. However, in the presence of Selected Availability (SA), a commercial user suffers degraded perfor- mance since the available P-code accuracy (nor- mally 30 ft la) is corrupted to the CA-code level of 100 ft la. SA corruption of the pseudorange measurement provides another error source that must be compensated for by the Kalman filter. This paper describes research performed at the Air Force Institute of Technology (AFIT) to im- plement course correction for the SA corruption by modifying the Kalman filter used in a typi- cal GPS/INS integration. Two modified filters are developed: one filter which models SA using individual error-states, and another filter which compensates for SA by simply increasing the mea- surement noise. Neither of these filters totally eliminates the corruption due to SA, but both provide a significant increase in the accuracy of the navigation position solution.
Published in:	Proceedings of the 48th Annual Meeting of The Institute of Navigation (1992) June 29 - 1, 1992 ANA Westin Hotel Dayton, OH
Pages:	297 - 306
Cite this article:	Negast, William J., Paschal, Randall N., "Coarse Correction of Selected Availability Affects Using Markov Models in an Extended Kalman Filter," Proceedings of the 48th Annual Meeting of The Institute of Navigation (1992), Dayton, OH, June 1992, pp. 297-306.
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