Integrity Methodologies for Aircraft Carrier Precision Approach and Landing

Bruce R. Peterson and Greg B. Johnson

Abstract:	Raytheon recently developed integrity methodologies as part of the US Navy sponsored Shipboard Relative GPS (SRGPS) project, which is a component of the military's Joint Precision Approach and Landing Systems effort (JPALS). One SRGPS goal is to demonstrate the use of GPS technology for aircraft carrier precision approach and landing. The algorithm invoked toward that goal is Relative Kinetic Carrier Phase Tracking. Carrier phase techniques require integrity verification of the ambiguity selection. The developed methodologies for integrity verification invoke a separation between the integrity of the ambiguity search space, and the integrity of the ambiguity selection itself. The first part of the development was a qualitative survey of the integrity problem. In concept, the visible GPS satellites yield a collection of ambiguity sets of which one and only one is the correct ambiguity set; the search volume is a sub-collection of the collection; and the elements of the search volume are the candidate ambiguity sets. The development identified the following three requirements: 1) the integrity method must establish, with high probability, that the correct ambiguity set is included in the search volume; 2) the integrity method must establish, with high conditional probability, that the correct ambiguity set will be selected, given that the correct ambiguity set is in the search volume; and, 3) the integrity method must establish, with high conditional probability, that every incorrect ambiguity set in the search volume will be rejected, given that the correct ambiguity set is not in the search volume. Requirement 1) is the integrity of the search space. Requirement 2) and 3) taken together is the integrity of the ambiguity selection. The second part of the development was an investigation of different methods of estimating integrity for Relative Kinematic Carrier Phase Tracking (RKCPT) ambiguity selection. The methods considered included the Threshold Method with several kinds of Ambiguity Metrics. The paper presents data resulting from the investigation. This paper demonstrates the importance of a pure threshold test to assure selection of the correct ambiguity set, given the levels required for a precision approach. The importance is that conditional probabilities 2) and 3) above can be replaced by the more efficient threshold test. The threshold test assures, to a high probability level, that if an ambiguity set is selected, then it is the correct ambiguity set. That is the same conclusion reached by taking 2) and 3) together. Finally, the paper gives the criteria for being able to use a threshold test.
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:	1280 - 1289
Cite this article:	Peterson, Bruce R., Johnson, Greg B., "Integrity Methodologies for Aircraft Carrier Precision Approach and Landing," 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. 1280-1289.
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