Optimal Augmentation of GPS using Inexpensive Geosynchronous Navigation Satellites

Sam Pullen and Bradford Parkinson

Abstract:	Programs sponsored by the U.S. Federal Aviation Administration (FAA) use the Global Positioning System (GPS) to support civil users with demanding navigation requirements. Ranging augmentations to GPS, such as pseudolites and new satellites, will be needed to provide sufficient availability for these applications. However, it may be prohibitively expensive to provide separate augmentations for each civil program. Geosynchronous satellites are one means to satisfy the needs of all proposed civil programs. These satellites would contain on-board atomic clocks to provide autonomous ranging as well as conveying the correction message generated by the Wide Area Augmentation System (WAAS). The projected performance of this satellite is used to select locations for a set of four such satellites that maximize the overall availability of the primary airborne applications now envisioned by the FAA. These include the Standard Positioning Service (SPS) with Receiver Autonomous Integrity Monitoring (RAIM) or the GPS Integrity Channel (GIC) provided by WAAS for enroute navigation to non-precision approach, the use of WAAS corrections to SPS for Category I precision approach, and the Local Area Augmentation System (LAAS) for Category III precision landing. Availability is assessed using RAIM horizontal protection limits for SPS and vertical protection limits for WAAS and LAAS. An evo-lutionary search method known as Simulated Annealing is used to find the optimal set of satellite locations. The results show that four optimally located geosynchronous satellites can satisfy the needs of all proposed FAA civil applications of GPS, performing the correction broadcast role for WAAS and reducing the need to purchase separate augmentations for the others. The primary issues yet to be resolved are the level of service to be provided by the satellite design and the responsibility for ground control and monitoring of the geosynchronous satellite constellation.
Published in:	Proceedings of the 10th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1997) September 16 - 19, 1997 Kansas City, MO
Pages:	1271 - 1281
Cite this article:	Pullen, Sam, Parkinson, Bradford, "Optimal Augmentation of GPS using Inexpensive Geosynchronous Navigation Satellites," Proceedings of the 10th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1997), Kansas City, MO, September 1997, pp. 1271-1281.
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