Wide-area differential operation of the global positioning system: Ephemeris and clock algorithms

The Global Positioning System (GPS) provides great potential benefit for commercial aviation because of its low-cost and seamless navigation. While accuracy requirements can be achieved, several technical challenges have to be resolved in order to use GPS as the primary navigation system. Among them, the stringent requirements for integrity, availability and continuity of service have demanded a new level of GPS navigation performance.; The Wide Area Augmentation System (WAAS) is being deployed by the Federal Aviation Administration (FAA) to augment GPS. WAAS will aid GPS with the following three services. First, WAAS uses a nationwide ground reference stations to monitor the health of all satellites over the national airspace system (NAS) and flag situations which may cause an integrity threat to flight safety. Secondly, WAAS uses the ground network to generate vector differential corrections which will improve navigation accuracy. Thirdly, it uses geostationary satellite(s) to broadcast differential corrections and integrity flags at the GPS L₁ frequency. These ranging signals will be combined with the GPS ranging signals to improve time availability and continuity of service.; This research work describes the ephemeris and clock algorithms which generate the differential corrections and their confidence values. These corrections and user differential range error (UDRE) estimates are capable of achieving accuracy requirements for Category I precision approach. Furthermore, integrity monitoring algorithms are implemented to examine navigation performance under system failure modes. This work shows that navigation performance (accuracy, availability and integrity) can be maintained even in the presence of failures. This robustness is demonstrated using real data and simulations.