Comparison of Fixed and Variable Threshold RAIM Algorithms

Mark A. Sturza and Alison K. Brown

Abstract:	GPS integrity monitoring is key to obtaining FAA approval for civil aviation use in the National Air Space (NAS). Receiver autonomous integrity monitoring (RAIM) is the simplest and mOSt cost effective technique for integrity monitoring. GPS navigation requires a minimum of four satellites. RAIM requires a minimum of five satellites. The redundant information is used for fault detection and isolation, For purposes of integrity monitoring a fault is defined as a pseudorange residual that results in a position error exceeding the specified acceptable limit. This paper provides a comparison of fixed and variable threshold algorithms. Fixed threshold algorithms provide constant false alarm rate (CFAR). The CFAR algorithm probability of detection varys as a function of the satellite geometry. A separate geometry check is required to determine when the algorithm is unreliable (probability of detection below a threshold value). Variable threshold algorithms provide constant probability of detection (CPOD). The CPOD algorithm probability of false alarm varies as a function of the satellite geometry. Thus as the satellite geometry degrades, the receiver noise naturally triggers an alarm. A separate geometry check is not required.
Published in:	Proceedings of the 3rd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1990) September 19 - 21, 1990 The Broadmoor Hotel Colorado Spring, CO
Pages:	437 - 443
Cite this article:	Sturza, Mark A., Brown, Alison K., "Comparison of Fixed and Variable Threshold RAIM Algorithms," Proceedings of the 3rd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1990), Colorado Spring, CO, September 1990, pp. 437-443.
Full Paper:	ION Members/Non-Members: 1 Download Credit Sign In