Independent Data Verification and Validation (IDV&V) Algorithms for WAAS and Preliminary Results

Scott Pogorelc, Alex Sasha Draganov, Brent Harding, Tim Cashin and Kelly Murdock

Abstract:	The National Satellite Testbed (NSTB) is being used to evaluate various aspects of the FAA’s Wide Area Augmentation System (WAAS) concept for enhancing GPS, including algorithms to perform an Independent Data Verification and Validation (IDVBrV) function for information being broadcast over the WAAS data link. IDV&V algorithms have been designed by STel to ensure the integrity and accuracy of the active data broadcast by an Inmarsat geostationary satellite. The basis of this IDV&V algorithm is to use a redundant or verification data stream (Stream A) to verify and validate the active corrections derived from the primary data stream (Stream A). The entire set of IDV&V algorithms is comprised of three main sections: User Differential Range Error (UDRE) verification and validation, Grid Ionospheric Vertical Error (GIVE) verification and validation and User Position Accuracy (UPA) validation. The GIVE verification and validation ensures that the User Ionospheric Vertical Error (UIVE), which is computed from the broadcast Grid Ionospheric Vertical Errors (GIVES), bounds the vertical ionospheric delay error in 99.9% of the cases within monitored ionospheric grid cells. This is performed in a three-stage process. First, the individual ionospheric delays computed from stream B dual-frequency data are compared to the interpolated delays at their respective pierce points and the residuals are mapped to the appropriate grid points. Second, for each ionospheric grid point, a 99.9% error bound is determined by applying a likelihood function to the magnitude of the residual errors. Finally, the broadcast GIVE is adjusted and/or a “Do Not Use” or “Not Monitored” GIVE value is issued for each grid point. Similarly, the UDRE verification and validation ensures that the broadcast User Differential Range Error (UDRE) bounds the post-corrected pseudorange residual in 99.9% of the cases for each and every active satellite. The algorithms consist of applying Stream A satellite ephemeris, fast clock and slow clock information to atmospherically-corrected Stream B pseudorange data. In the same manner as that used for the GIVE, the 99.9% error bound is determined by applying a likelihood function to the magnitude of the residual errors. The broadcast UDRE is adjusted and/or a “Not Monitored” or “Do Not Use” correction value is issued for each satellite. The UPA validation is a final composite check of the broadcast information, including ionospheric grid delays, satellite long-term and fast corrections and other active data. The algorithm estimates the position error of each stream B monitor station using the active NSTB broadcast information and the corresponding surveyed position.
Published in:	Proceedings of the 9th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1996) September 17 - 20, 1996 Kansas City, MO
Pages:	813 - 825
Cite this article:	Pogorelc, Scott, Draganov, Alex Sasha, Harding, Brent, Cashin, Tim, Murdock, Kelly, "Independent Data Verification and Validation (IDV&V) Algorithms for WAAS and Preliminary Results," Proceedings of the 9th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1996), Kansas City, MO, September 1996, pp. 813-825.
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