The Effect of Uncertain Covariance on a Chi-Square Integrity Monitor

Jason H. Rife

Peer Reviewed

Abstract:	This paper presents a method for overbounding integrity risk for chi-square monitors, which detect anomalies by analyzing the two-norm of a vector of input signals. Aircraft navigation examples of chi-square monitors include many Receiver Autonomous Integrity Monitoring (RAIM) algorithms as well as fault-specific detection algorithms in space-based and ground-based augmentation systems for GNSS (e.g., signal deformation monitoring and ionosphere gradient monitoring). Simple inflation of the noise model for the input-data vector does not always ensure conservative bounding, particularly for unfavorable fault cases. To ensure integrity in such fault cases, this paper introduces a conservative modeling approach for replacing a generalized chi-square distribution with a conventional chi-square distribution. This conservative model relies on bracketing the range of variation of the input-data covariance matrix between an upper and a lower bound.
Published in:	NAVIGATION: Journal of the Institute of Navigation, Volume 60, Number 4
Pages:	291 - 303
Cite this article:	Rife, Jason H., "The Effect of Uncertain Covariance on a Chi-Square Integrity Monitor", NAVIGATION: Journal of The Institute of Navigation, Vol. 60, No. 4, Winter 2013, pp. 291-303.
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