A New Approach to GPS Integrity/Availability: Immediate Global Sole Means Without WAAS

John Diesel

Abstract:	GPS has the required accuracy for all phases of navigation, including en-route and non-precision approach. It also has the accuracy required for precision approach and landing, when augmented by Local Area DGPS (LADGPS), using techniques such as kinematic carrier phase tracking. However, questions still remain about integrity, availability, and continuity. This paper first shows that any approach and landing system based on position information alone is inherently unstable. This makes it especially vulnerable to lags, gaps, noise, or interference in the data. These problems can be overcome by using aircraft autonomous integrity monitoring with extrapolation. By storing the averaged GPS measurements at 2.5 minute time intervals in a circular buffer for 30 minutes or more, satellite clock drifts of any magnitude can be detected with as few as three or four satellites for long periods. All valid past and present GPS measurements can then be used to estimate present position by extrapolation. This results in a sole means non-precision approach world-wide availability of .99999, based on constellations from 21 to 24 satellites, without using WAAS. Also, the conditional probability of detecting a failure, assuming it has occurred, will be increased from .999 to .99999.
Published in:	Proceedings of the 7th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1994) September 20 - 23, 1994 Salt Palace Convention Center Salt Lake City, UT
Pages:	567 - 576
Cite this article:	Diesel, John, "A New Approach to GPS Integrity/Availability: Immediate Global Sole Means Without WAAS," Proceedings of the 7th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1994), Salt Lake City, UT, September 1994, pp. 567-576.
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