Providing Precision Approach SBAS Service and Integrity in Equatorial Regions

D. Cormier, E. Altshuler, P. Shloss

Abstract:	We report results of a study designed to determine how one would safely reduce bounds on ionospheric errors so that a Space Based Augmentation System (SBAS) would be able to provide single frequency precision approach SBAS service in the presence of the ionospheric effects common to the equatorial region. We work under the restrictions of the ICAO Standards And Recommended Practices for GNSS (SARPs) [1], which specifies a 5-by-5 degree grid of Ionospheric Grid Points, a thin shell model of the ionosphere with a shell height of 350 km, and an ionospheric message structure commensurate with that used by the Wide Area Augmentation System (WAAS). First, we study the applicability of WAAS algorithms suitably modified to account for larger spatial variability and enhanced using techniques recently developed to improve WAAS ionospheric storm day performance. This exercise allows us to demonstrate the importance of tailoring SBAS ionospheric algorithms to the prevailing environmental conditions. This is followed by a discussion of techniques that might allow integrity proofs to be completed for users in the presence of the types of ionospheric irregularities regularly encountered in the equatorial region. In conclusion we assess the prospects for providing single frequency precision approach SBAS service in equatorial regions without any changes to the SARPs. We list outstanding challenges to providing such service, and discuss the assumptions behind our assessment. Finally, we entertain the possibility that techniques developed for dealing with equatorial ionospheric threats might be applied to WAAS in order to improve WAAS threat models and the way that WAAS deals with significant ionospheric irregularities.
Published in:	Proceedings of the 16th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS/GNSS 2003) September 9 - 12, 2003 Oregon Convention Center Portland, OR
Pages:	1728 - 1735
Cite this article:	Cormier, D., Altshuler, E., Shloss, P., "Providing Precision Approach SBAS Service and Integrity in Equatorial Regions," Proceedings of the 16th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS/GNSS 2003), Portland, OR, September 2003, pp. 1728-1735.
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