Wide-area differential GPS reference-station placement

A wide-area differential Global Positioning System (GPS) augmentation system provides differential corrections to GPS users in a large, but bounded, service area. Wide-area differential corrections are of two basic types: satellite-ephemeris/clock corrections and ionospheric-delay corrections. The underlying differences between the two types of corrections and the measurements used to calculate them impose different requirements on the placement density of the reference stations. There are also unique placement requirements near the boundaries of the service area. This paper presents guidelines for reference-station placement to provide the required navigation accuracies for aviation precision approach and other navigation modes of flight. The differential-correction accuracies for various reference-station placements are analyzed. The computer modeling tool used to verify and illustrate placement principles is Rockwell's Satellite-Based Air Traffic Management Accuracy Performance Model (SAPM).