GPS signal selective availability-modelling and simulation for FAA WAAS IV&V

FAA is currently developing a wide area augmentation system (WAAS) to improve the accuracy, availability, continuity, and integrity of the Global Positioning System (GPS) for civil aviation applications. The initial WAAS (IWAAS) is planned to provide operational capability over the entire continental US airspace, from en-route down to Cat I Precision Approach, by the end of 1998. Illgen Simulation Technologies, Inc. is currently involved with independent verification and validation (IV&V) of the system software. To verify alternative WAAS designs, an IWAAS simulator (iWAASs) has been developed at ISTI. This paper presents a design study of selective availability (SA) modeling and simulation suitable for implementation in iWAASs. It gives a detailed description of the mathematical procedures of SA modeling. Autoregressive moving-average modeling techniques are used. Data collected from FAA flight tests is used to derive the SA models; these models are then used to generate simulated SA in iWAASs. A number of techniques, which can be used to analyze and verify the derived SA models, are described. Limitations of the approach and the resulting SA models are discussed, and future directions of work are identified