RAIM Availability for Cat IIIB Operation

Ronald Brown, Richard Hall, Glyn Romrell, and James Waid

Abstract:	Current demonstrations of aircraft automatic landing using DGPS operation show that the navigation accuracy required for CAT IIIb operation can be met. A key issue that must be resolved prior to acceptance of DGPS operation is verification that the DGPS navigation solution meets stringent FAA availability and continuity of operation specifications. Current approaches to this problem rely on GPS Receiver Autonomous Integrity Monitoring (RAIM) techniques to avoid the use of additional, independent navigation reference systems. The basic RAIM procedure is to assume or measure the GPS receiver noise level, set a detection threshold that provides a specified probability of false alarm (Pfa), compute a maximum undetectable single measurement bias error given a specified probability of missed detection (Pmd) and then compute the position error corresponding to that single bias error to determine if the required navigation performance (RNP) is being met. The RAIM approach described in this paper is a variation of the current procedure in that the required receiver noise is computed such that the Pfa, Pmd and RNP requirements will be simultaneously satisfied. If the actual receiver noise is less than the computed noise, then the availability and continuity of operation requirements will be met. A second issue addressed in this paper relates to the assumption of only a single measurement bias error. Multiple bias errors due to multipath and/or phase ambiguity errors could cause unacceptably large navigation errors in the presence of “bad” GPS satellite geometry. The use of carrier phase DGPS processing results in very low noise levels and permits detection of “small” bias errors. An extension of the maximum likelihood single bias fault isolation procedure is described which may provide a capability to isolate and remove multiple biases.
Published in:	Proceedings of the 51st Annual Meeting of The Institute of Navigation (1995) June 5 - 7, 1995 Antlers Doubletree Hotel Colorado Springs, CO
Pages:	381 - 389
Cite this article:	Brown, Ronald, Hall, Richard, Romrell, Glyn, Waid, James, "RAIM Availability for Cat IIIB Operation," Proceedings of the 51st Annual Meeting of The Institute of Navigation (1995), Colorado Springs, CO, June 1995, pp. 381-389.
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