Hybrid GPS Constellations to Provide High Availability of Cat I Precision Approach, RAIM, and Continuity

Clifford W. Kelley and Kenneth F. Davis

Abstract:	Problem: Previous studies have shown that constellations designed for availability of Category I precision approach are best served with 3 plane constellations while RAIM (Receiver Autonomous Integrity Monitoring) and Continuity is best obtained with 6 or more planes. Solution: A study of constellations, which have 6 planes where 3 of the planes have more satellites than the other 3 was conducted. This “hybrid” constellation provides features of both 6 and 3 plane constellations. These constellations were analyzed to determine how well Cat I precision approach, RAIM, and Continuity could be simultaneously achieved. With a UERE of 1 meter and a mask angle of 5 degrees a 24 satellite constellation in 3 planes can meet the Category I precision approach accuracy requirement 99% of the time worldwide and provide a minimum of 6 satellites in view. Adding 12 satellites in 3 planes between the first 3 provides almost 10 in view. This provides RAIM/Continuity availability nearly equivalent to a 6 plane 36 satellite constellation while providing a higher availability of Cat I precision approach than the 6 plane constellation could. This advantage is even greater when the mask angle is increased from 5 degrees. The analysis of the trade-off of availability of Category I and RAIM/Continuity was performed for hybrid constellations ranging from 30 to 36 satellites. In each case availability of Cat I was not as good as the equivalent 3 plane constellation alone but the RAIM/Continuity was as nearly as good as the equivalent 6 plane constellation.
Published in:	Proceedings of the 13th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2000) September 19 - 22, 2000 Salt Palace Convention Center Salt Lake City, UT
Pages:	2184 - 2190
Cite this article:	Kelley, Clifford W., Davis, Kenneth F., "Hybrid GPS Constellations to Provide High Availability of Cat I Precision Approach, RAIM, and Continuity," Proceedings of the 13th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2000), Salt Lake City, UT, September 2000, pp. 2184-2190.
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