RAIM with Kalman Code Carrier Smoothing

Nicolas Martin, David Depraz, Herve Guichon

Abstract:	Today in aeronautical receivers the integrity monitoring is not sufficient to deal with all phases of flight, noticeably due to the risk of unforeseeable geometry outage, for instance in case of satellite masking or failure. The use of carrier phase measurement is known as a good candidate to propagate the position and keep small protection radii in that event. The aim of the paper is to present a way of implementing this technique by integrating an optimal code carrier smoothing in the PVT. The paper begins by a characterization of code and carrier phase measurements, with complementary performances. It presents, for comparison, different methods of code carrier smoothing, from the standard technique to the optimal implementation with a 6 state Kalman filter defined according to the measurement model. The aim of the optimal smoothing is to provide a reliable characterization of standard deviation for integrity monitoring. The integration of the optimal smoothing in the PVT is detailed, with the description of the application of the maximum separation method. Simulation results show the benefit of the method in terms of continuity improvement, as compared with the standard snapshot RAIM. The method keeps unmodified protection radius in case of sudden geometry degradation, at least for a few minutes, whilst taking instantaneously benefit of geometry improvement in case of new satellite. The continuity is guaranteed as long as at least 5 satellites are available at each time, not necessarily the same at all times. The use of the method in case of bi-frequency receiver is presented, with improved simulation results. The paper presents the possible application to GBAS system, with code and carrier correction for optimised smoothing. Although requiring heavy computations, the algorithm has low complexity and high robustness. The impact on CPU load should not be a feasibility issue . Before entering a critical phase of flight, the guarantee to keep an unmodified protection radius for a given time is decisive for safety. It changes a continuity issue to a short term availability problem.
Published in:	Proceedings of the 25th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2012) September 17 - 21, 2012 Nashville Convention Center, Nashville, Tennessee Nashville, TN
Pages:	2259 - 2274
Cite this article:	Martin, Nicolas, Depraz, David, Guichon, Herve, "RAIM with Kalman Code Carrier Smoothing," Proceedings of the 25th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2012), Nashville, TN, September 2012, pp. 2259-2274.
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