Autonomous Integrity Monitoring for Precision Approach Using DGPS and a Ground-Based Pseudolite

Boris S. Pervan, Clark E. Cohen, and Bradford W. Parkinson

Abstract:	Although DGPS is inherently robust to space-vehicle- related errors, faihues in the differential station or airborne receiver can be a threat to continuous precise positioning. The extreme reliability required for precision approach, therefore, establishes the need for an active integrity verijication system. Traditional RAM concepts make use of redundant spacecraft and are limited by availabifi@ of strong spacecraft geometry. Furthermore, integrity verification algorithms based on redundant space vehicles could be susceptible to intentional tampering with the reference station or differential correction uplink. Carrier-tracking of ground-based pseudolites can provide comprehensive integrity. The centimeter-level accuracy provided by GPS carrier phase allows extremely tight detection thresholds to be set. The effect is that ranging or system errors resulting in position fixes outside Category III specifications are detectable. The Kinematic GPS Landing System (KGLS) developed at Stanford University already uses carrier phase measurements from ground-based pseudolites known as GPS Marker Beacons to resolve integer cycle ambiguities. Once cycle ambiguities are determined, carrier-based spacecraft ranging provides the accuracy for Category III precision landing. During approach, however, a pseudolite can also function as a redundant ranging source, and thus provide the means for autonomous integrity monitoring. The proximity of the pseudolite and the large geometry change that occurs during aircraft overflight can be used to detect intentional tampering with the reference station or differential correction uplink. The potential for autonomous integrity verification for Category III approach is demonstrated through analysis, simulation, and flight tests performed in a singleengine Piper Dakota.
Published in:	Proceedings of the 6th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1993) September 22 - 24, 1993 Salt Palace Convention Center Salt Lake City, UT
Pages:	475 - 485
Cite this article:	Pervan, Boris S., Cohen, Clark E., Parkinson, Bradford W., "Autonomous Integrity Monitoring for Precision Approach Using DGPS and a Ground-Based Pseudolite," Proceedings of the 6th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1993), Salt Lake City, UT, September 1993, pp. 475-485.
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