Analysis of the Effects of Earth-Surface Based Multipath Reflections on GPS Code-Phase Measurements

Daniel N. Aloi and Frank van Graas

Abstract:	Multipath is the dominant error source in differential Global Positioning System (DGPS) applications. In order to characterize the effects of earth-surface based multipath reflections on the pseudorange measurements, a signal model is needed. A mathematical model is developed which characterizes the earth as a lossy medium. This scenario gives rise to a single multipath reflection. The model takes into account the variation of amplitude and phase of the multipath signal due to wave travel in air, the reflection of a wave at a boundary separating two media, and the effects of the antenna radiation pattern. In the paper, this model is validated with real GPS data. The validation is performed for salt water, which is a reflector that could be encountered at a ground reference site. All validations are performed with receivers that employ a non-coherent tracking loop. These results characterize the multipath signal in terms of its relative amplitude, relative time-delay, relative phase-delay, and relative phase-rate-of-change. The knowledge of these parameters help determine the type of antenna patterns and tracking loops that are needed for specific DGPS applications. Also, it is a very a useful tool to investigate the effects of a changing environment at a DGPS ground reference site.
Published in:	Proceedings of the 55th Annual Meeting of The Institute of Navigation (1999) June 27 - 30, 1999 Royal Sonesta Hotel Cambridge, MA
Pages:	609 - 618
Cite this article:	Aloi, Daniel N., van Graas, Frank, "Analysis of the Effects of Earth-Surface Based Multipath Reflections on GPS Code-Phase Measurements," Proceedings of the 55th Annual Meeting of The Institute of Navigation (1999), Cambridge, MA, June 1999, pp. 609-618.
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