Overview of the WAAS Integrity Design

M.S. Grewal, H. Habereder, T.R. Schempp

Abstract:	The objective of the Wide Area Augmentation System (WAAS) is to enhance the GPS standard positioning service providing sufficient integrity, accuracy, availability and continuity for use in commercial aviation. Integrity is defined as the ability of the system to provide timely warnings to the user when individual corrections or certain satellites should not be used for navigation, i.e., the prevention of hazardously misleading information (HMI) data transmission to the user. The system should not be used for navigation when hardware, software or environmental errors directly pose a threat to the user or indirectly pose a threat by obscuring HMI from the integrity monitors. WAAS integrity is based on the premise that errors not detected or corrected in the operational environment can become threats to integrity, and if not mitigated, can become hazards to the user. The FAA certified the WAAS system for operational use on July 10, 2003. The system provides enroute through non-precision approach and LNAV/VNAV as well as LPV approach capabilities. WAAS is the first Satellite Based Augmentation System (SBAS) system certified for use in commercial aviation. Certification was the culmination of an extensive safety assurance analysis required to prove that WAAS meets its integrity requirements. In particular, the safety assurance effort identified and mitigated a long list of error sources which could potentially become integrity threats. This paper will show how the WAAS design mitigates the majority of these data errors with corrections and any remaining errors with statistically derived error bounds. WAAS corrections improve the accuracy of GPS and GEO satellite signals. The integrity data ensures that the residual errors are bounded. The WAAS integrity monitors help ensure that the integrity data has not been corrupted by WAAS failures. This paper will also provide a list of the data errors, error detection and correction pitfalls, and a discussion on how such errors may be mitigated.
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:	2750 - 2759
Cite this article:	Grewal, M.S., Habereder, H., Schempp, T.R., "Overview of the WAAS Integrity Design," 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. 2750-2759.
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