Validation Analysis of the WAAS GIVE and UIVE Algorithms

Reza Ahmadi, Gregory S. Becker, Stephen R. Peck, Francois Choquette, Thomas F. Gerard, Anthony J. Mannucci, Byron A. Iijima, and Angelyn W. Moore

Abstract:	As a part of its “slow” error corrections, the Federal Aviation Administration’s Wide-Area Augmentation System (WAAS) provides ionospheric vertical delays at geographically fixed Ionospheric Grid Points (IGPs). In addition to these vertical delays, WAAS’s message type 26 contains Grid Ionospheric Vertical Errors (GIVES) for the IGPs. GIVE values are required to bound the actual error with 99.9% confidence. Using the GIVE values a user can compute the User Ionospheric Vertical Errors (UIVEs) at each of his ionospheric pierce point locations. The UIVE scaled by an obliquity factor (F) is required to bound the users’ ionospheric slant error at their pierce points with 99.9% confidence. In this paper we report the performance analysis of GIVE and UIVE algorithms using both simulated and real data. Several algorithm modification are considered. The 3 dimensional electron density of the ionosphere is simulated by the FAIM model. Phase one WAAS geometry (24 sites, 24 GPS satellites) is used in this analysis. The simulated users (162) are distributed across the CONUS. The analysis compares the user’s slant ionosphere delay error to the UIVE value to determine if integrity requirements are met. Performance is analyzed, using a solar maximum scenario. Analysis shows that performance improvement is possible with the GIVE / UIVE modifications that still maintain the required integrity. Analysis of 26 days of real data, including one ionospheric storm, also demonstrates the 99.9% bounding integrity. Real data analysis demonstrates better performance, however, the ionosphere is currently near solar minimum as opposed to the solar maximum conditions that were simulated.
Published in:	Proceedings of the 53rd Annual Meeting of The Institute of Navigation (1997) June 30 - 2, 1997 Albuquerque, NM
Pages:	441 - 450
Cite this article:	Ahmadi, Reza, Becker, Gregory S., Peck, Stephen R., Choquette, Francois, Gerard, Thomas F., Mannucci, Anthony J., Iijima, Byron A., Moore, Angelyn W., "Validation Analysis of the WAAS GIVE and UIVE Algorithms," Proceedings of the 53rd Annual Meeting of The Institute of Navigation (1997), Albuquerque, NM, June 1997, pp. 441-450.
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