Analysis of Iridium-Augmented GPS for Floating Carrier Phase Positioning

Abstract

Carrier-phase ranging measurements from Global Positioning System (GPS) and low-Earth-orbiting Iridium telecommunication satellites are integrated in a precision navigation system named iGPS. The basic goal of the system is to enhance GPS positioning and timing performance, especially under jamming. In addition, large satellite geometry variations generated by fast-moving Iridium spacecraft enable rapid estimation of floating cycle ambiguities. Augmentation of GPS with Iridium satellites also guarantees signal redundancy, which enables Receiver Autonomous Integrity Monitoring (RAIM). In this work, parametric models are developed for iGPS measurement error sources and for wide-area corrections from an assumed network of ground reference stations. A fixed-interval positioning and cycle ambiguity estimation algorithm is derived and a residual-based carrier-phase RAIM detection method is investigated for integrity against single-satellite step and ramp-type faults of all magnitudes and start-times. Predicted overall performance is quantified for various ground, space, and user segment configurations.