Modelling and simulation of WADGPS systems

To meet the need of demanding navigation accuracy over the coastal ocean, in particular, in harbor entrances, DGPS systems of various enhanced navigation capabilities are developed. This paper briefly reviews the concept of Wide Area DGPS (WADGPS) and points to the potential benefit of this new DGPS technology to the marine community. The paper illustrates a WADGPS system being implemented by the Federal Aviation Administration (FAA) for civil aviation application - the GPS Wide Area Augumentation System (WAAS). To verify alternative WAAS designs, Illgen Simulation Technologies, Inc. (ISTI) has developed an initial WAAS (I-WAAS) simulator (iWAASs). The iWAASs is designed to evaluate with high confidence the performance of the I-WAAS design. A key element of the iWAASs is a set of “golden scenarios” which simulate the operation conditions of the physical system. The basic building blocks of the iWAASs are a set validated models which take into account various effects and sources of error of GPS and WAAS. Among these, selective availability (SA) and ionospheric delay errors are two largest sources of error of critical importance. The paper presents a design study SA modeling and simulation implemented in iWAASs. It gives a detailed description of the mathematical procedures of SA modeling. Auto-regressive moving-average (ARMA) modeling techniques are used. Data collected from FAA flight tests is used to derive the SA models and these models are then used to generate simulated SA. A number of techniques, which can be used to analyze and verify the derived SA models, are described