Evaluating Candidate Algorithm and Architecture Improvements for the Next Phase of WAAS

C. Griffith, H. Wan, H. Go, E. Carolipio

Abstract:	Raytheon is currently completing development of the Wide-Area Augmentation System (WAAS) – a GPS based augmentation system that is intended to become the primary navigational aid for commercial aviation during all phases of flight. As WAAS nears its initial operating capability (IOC) phase, potential upgrades to the system to achieve final operating capability (FOC) are being laid out. The primary goal of FOC can be loosely described as providing lateral precision with vertical guidance (LPV) service throughout the entire WAAS Continental United States (CONUS) service volume virtually all (99-100%) of the time. A combination of enhancements from both algorithms and architecture will be required to achieve this goal. This paper reviews the list of candidate algorithm and architecture improvements currently being explored by the WAAS program for FOC and the method for evaluating them. Algorithm candidates include enhancements to the existing Grid Ionosphere Vertical Error (GIVE) and User Differential Range Error (UDRE) algorithms, as well as better measurement data screening. As papers discussing GIVE and UDRE algorithm enhancements have been presented at previous, as well as this current, ION conferences, they will be discussed only briefly here. Architecture enhancement candidates include upgrades to the existing WAAS receiver network to gain service for critical regions of the WAAS service volume. The approach taken by WAAS focused on the gain in coverage for six critical points, or “users”, with each system or algorithm enhancement. These six critical points represent areas at the fringes of the WAAS CONUS service volume. The candidate enhancement is then scored on the basis of how much coverage is gained by the critical points. The top scoring enhancements were then combined to give an estimate of the overall service availability, or coverage. The WAAS Service Volume Model (SVM) software is used to estimate the availability of LPV service and was the primary tool used to conduct the analysis. The SVM includes models for the GPS satellite motion, receiver network and for the candidate algorithm enhancements. The preliminary SVM results will be provided and illustrate a potential list of system enhancements to pave the road to achieving WAAS FOC.
Published in:	Proceedings of the 2003 National Technical Meeting of The Institute of Navigation January 22 - 24, 2003 Disneyland Paradise Pier Hotel Anaheim, CA
Pages:	203 - 213
Cite this article:	Griffith, C., Wan, H., Go, H., Carolipio, E., "Evaluating Candidate Algorithm and Architecture Improvements for the Next Phase of WAAS," Proceedings of the 2003 National Technical Meeting of The Institute of Navigation, Anaheim, CA, January 2003, pp. 203-213.
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