Receiver Autonomous Mitigation of GPS Non-Line-of-Sight Multipath Errors

A. Morrison, S. Krishnan, A. Anpalagan, and B. Grush

Abstract:	Accurate positioning of stationary assets or locations in heavy multipath environments (urban canyon, steep terrain) remains a difficult problem when using simple navigation-grade GNSS receivers. Non line-of-sight (NLoS) multipath error is a significant contributor to this problem. The promise of reliable, 1 meter accuracy for Galileo will not be achieved in deep urban canyon unless multipath errors, especially NLoS errors, are mitigated at the receiver. We propose an iterative position comparison method of determining whether a given constellation contains measurements distorted by NLoS propagation, as well isolating which of the available pseudoranges are most likely affected by NLoS error. This method involves utilizing the characteristic and extent to which an overspecified (more than four signals) position solution differs as candidate signals for NLoS disturbance are included or excluded from the solution. We tested this method by collecting relatively clean GPS pseudorange data from the roof of a multi-storey apartment building in downtown Toronto and simulated NLoS errors by injecting various levels of artificial NLoS propagation delay in order to study our ability to detect these delays intermixed with other signals as collected. When this method is optimized it will form the basis of a procedure that will select best-subsets of pseudoranges on a temporal window-by-window basis, in order to allow short intervals of urban canyon data to be used to generate accurate, reliable, and repeatable position solutions for inexpensive stationary GNSS receivers, that would otherwise not be possible without longer periods of sustained data collection or the use of more expensive survey-grade devices. While early results show promise in detecting ranges of NLoS delay common in the urban canyon, more work is needed to increase the algorithm hit-rate and decrease its miss-rate, as well as to provide dynamic sensitivity threshold levels to best suit current environmental conditions.
Published in:	Proceedings of the 2006 National Technical Meeting of The Institute of Navigation January 18 - 20, 2006 Hyatt Regency Hotel Monterey, CA
Pages:	141 - 148
Cite this article:	Morrison, A., Krishnan, S., Anpalagan, A., Grush, B., "Receiver Autonomous Mitigation of GPS Non-Line-of-Sight Multipath Errors," Proceedings of the 2006 National Technical Meeting of The Institute of Navigation, Monterey, CA, January 2006, pp. 141-148.
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