A GPS Precision Approach and Landing System

Alison K. Brown

Abstract:	A GPS precision approach and landing system is described in this paper which provides a CAT 2 precision approach and landing capability. The system uses a Differential Carrier Ranging (DCR) positioning technique which combines pseudo-range, carrier phase, and differential corrections to compute a highly precise navlgation solution in real-time. A major problem with any aviation application of GPS is guaranteeing continuity of service, rellbility, and integrity. This problem is solved in the proposed approach and landing system through the use of pseudo&s to augment the GPS constellation. Pseuddites are ground based transmitters which broadcast a GPS-like signal that can be used as an additional range measurement by receivers. In the past, pseuddites have been proposed that operate at the Ll frequency. However, these interfere with the GPS signals whenever a receiver approaches too close to the pseudolite. Thii problem is solved in the proposed system by broadcasting the pseudolite signals in the aeronautical radionavigation (eatth-to- space) band. This is roughly 50 MHz above the Ll GPS frequency, and so does not interfere with GPS receiver operation. An advanced GPS receiver has been designed by NAVSYS which provides the capability of making measurements on the GPS signals, the PL signals, and also on GLONASS satellite signals if desired. The PL signal also acts as a communication link for the differential corrections, providing a data rate of 1000 bps with a BER of 10-l’. System integrity is assured through the use of a Receiver Autonomous integrity Monitoring (RAlM) algorithm onboard the aircraft receiver. Simulation results have shown that this algorithm can reliably detect and isolate satellite failures in real-time from the differential carrier range measurements. The combination of the GPS satellite and the pseudolite observations provides sufficient redundancy that 100% availability can always be guaranteed.
Published in:	Proceedings of the 5th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1992) September 16 - 18, 1992 Albuquerque, NM
Pages:	373 - 381
Cite this article:	Brown, Alison K., "A GPS Precision Approach and Landing System," Proceedings of the 5th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1992), Albuquerque, NM, September 1992, pp. 373-381.
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