Mitigation of Multipath in DGPS Ground Reference Stations

Michael S. Braasch and Frank van Graas

Abstract:	Multipath represents one of the most serious threats to accuracy in Differential GPS (DGPS). However, over the past few years a number of techniques have been developed to combat this problem. The theoretical foundations of multipath are presented and several multipath mitigation techniques are reviewed. Special emphasis is placed on signal diffraction methods. Diffraction from, for instance, antenna ground plane edges induces significant distortions in the radiation pattern of the antenna. Although this would seem to be undesirable, it can actually be used to mitigate the errors caused by signals reflecting from nearby objects. The process is known as multipath randomization and it simply involvesjittering the antenna and ground plane with respect to the reflecting surfaces. Reflections enter peaks and nulls in the distorted antenna pattern in a random manner. This coupled with the oscillations in relative phase (with respect to the direct signal) result in a multipath error signature which is noise-like. Since it is noise-like it may be significantly reduced by averaging the code phase measurements against the more stable carrier-phase measurements. Exploitation of this effect to reduce multipath error represents a significant increase in accuracy for real time DGPS. Experiments have been performed which verify these conclusions.
Published in:	Proceedings of the 1992 National Technical Meeting of The Institute of Navigation January 27 - 29, 1992 Catamaran Resort Hotel San Diego, CA
Pages:	105 - 114
Cite this article:	Braasch, Michael S., van Graas, Frank, "Mitigation of Multipath in DGPS Ground Reference Stations," Proceedings of the 1992 National Technical Meeting of The Institute of Navigation, San Diego, CA, January 1992, pp. 105-114.
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