Improved Iono PHMI Calculation for SBAS Systems

Christoph Mayer and Juan Blanch

Abstract:	Besides the wide-area augmentation system (WAAS) in the US, an increasing number of space-based augmentation systems (SBAS) are being developed or planned, such as the European Geostationary Navigation Overlay System (EGNOS) in Europe, the Multifunctional Satellite Augmentation System (MSAS) system in Japan, and the future Ground-based Regional Augmentation System (GRAS) in Australia and the GPS and Geo Augmented Navigation (GAGAN) system covering the Indian subcontinent. The integrity analysis in a given SBAS system includes calculating the probability of hazardous misleading information (PHMI) for the vertical ionospheric delays. We show that the built-in conservatism in the PHMI treatment that has been proposed for WAAS can be significantly reduced by using a more general model for the ionospheric process noise, i.e. we consider generalized models of the process noise, where the process noise is allowed to depend non-linearly on the chi-square statistic of the ionospheric measurement residuals. As a consequence, we obtain a more realistic dependence of PHMI on the ionospheric state, and the additional degrees of freedom of the process noise model can be used to optimize the system for availability under moderately disturbed ionospheric conditions.
Published in:	Proceedings of the 2009 International Technical Meeting of The Institute of Navigation January 26 - 28, 2009 Disney's Paradise Pier Hotel Anaheim, CA
Pages:	875 - 880
Cite this article:	Mayer, Christoph, Blanch, Juan, "Improved Iono PHMI Calculation for SBAS Systems," Proceedings of the 2009 International Technical Meeting of The Institute of Navigation, Anaheim, CA, January 2009, pp. 875-880.
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