Assessment of GPS Signal Multipath Interference

Sung H. Byun, George A. Hajj and Lawrence E. Young

Abstract:	Multipath is the phenomenon where a signal arrives at an antenna via several paths due to signal reflection and diffraction. These paths are superimposed on the direct signal at the antenna with a different phase and amplitude, and can result in significant ranging errors. A multipath simulator, MUSTARD (MUltipath Simulator Taking into Account Reflection and Diffraction), has been developed at the Jet Propulsion Laboratory. In essence, the simulator traces the signal as it is transmitted by the GPS satellite to a user's receiver accounting for all possible paths the signal can take by reflecting or diffracting from the surrounding sur- faces. The simulator uses simplified model of the real mul- tipath environment. In modeling the reflection and diffrac- tion from each surface, the Geometric Theory of Diffraction (GTD) is used. The multipath signals are then added to the direct signal after accounting for the gain of the receiving an- tenna. The receiver's tracking loop is then simulated and then range and phase multipath error are estimated. The multipath simulator can be used in the initial design phase of an experiment to identify hazardous environmental configuration that can cause severe multipath. By using the simulator we can also assess the upper limits on the antenna backlobes gains, and be able to determine the ideal antenna location, height, and orientation to minimize the multipath error within a given environment. Once the optimal geometric configuration is determined, it can provide a realistic quantitative estimate of multipath errors on GPS data. This in turn can provide means of testing different ways of analyzing the data to reduce the solution errors from multipath. With a given environment, this simulator is a valuable tool to quantitatively assess the multipath effect on the GPS measurement.
Published in:	Proceedings of the 2002 National Technical Meeting of The Institute of Navigation January 28 - 30, 2002 The Catamaran Resort Hotel San Diego, CA
Pages:	694 - 705
Cite this article:	Byun, Sung H., Hajj, George A., Young, Lawrence E., "Assessment of GPS Signal Multipath Interference," Proceedings of the 2002 National Technical Meeting of The Institute of Navigation, San Diego, CA, January 2002, pp. 694-705.
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