Wide Area Differential GPS

GPS has proven to be an extremely accurate positioning sensor for a wide variety of applications. However, in some situations, such as aircraft approach and landing, higher accuracy is required. Wide Area Differential GPS (WADGPS) is a system that could be used to meet such requirements. The WADGPS system comprises a master station, and local monitor stations distributed across the United States. The system calculates and transmits a vector of error corrections to users. This correction vector consists of parameters describing the three-dimensional ephemeris errors, satellite clock offsets, and ionospheric time delay parameters. The master station gathers GPS measurements made at each of the local stations, and estimates the errors using a combination of nonlinear static estimation and batch least squares. The performance of a 15-station WADGPS network was investigated by simulation for users at sites across the United States. The monitor stations were located at existing Loran or VOR stations. Simulation results indicate that normal GPS positioning errors can potentially be reduced by more than 95 percent using WADGPS.