Analysis and generalization of a dual-antenna multipath mitigation technique.

Marcelo C. Santos and Julio C. Farret

Abstract:	We have developed an approach for multipath mitigation which uses a configuration based on two closely spaced antennas linked to a single GPS receiver. As both antennas collect carrier phase observations to a particular satellite they are differenced forming a residual carrier phase single difference, which contains only multipath and noise. The residual carrier phase single difference observations feed an extended Kalman filter, which has as output the estimated multipath parameters for that particular geometric situation. A Gauss-Markov process is used in the filter. Our methodology introduces a temporal factor in the measurements in order to have enough redundancy to allow the estimation process to be carried out. Therefore, the estimated multipath parameters represent multipath for a small period of time depending on the sampling rate (e.g., 4 seconds for a sampling rate of 1 Hz). This temporal factor is justified under the assumption that multipath parameters and satellite geometry have a slow variation in time and space. After estimating the multipath parameters for the duration of the satellite pass, we can mitigate it from the original carrier phase observations. Data setswere used for testing the multipath mitigation technique. Different satellites passes at different azimuth and elevation angles over consecutive days under the same scenario were used. Daily repeatability analysis was used to ascertain the presence of multipath. The correlation between the estimated multipath vis-à-vis the measured one reached up to 80%. We also evaluated the performance of the multipath parameter estimation by means of spectral analysis. We compared a multipath signal, generated using the estimated multipath parameters, with the original input data that feeds the estimation process (the residual carrier phase single difference). The result shows that the spectral characteristic of the input residual single difference is similar to the signal computed using the estimated multipath parameters. This comparison suggests the efficiency of the estimation process. We have generalized the dual-frequency approach for a single dual-frequency receiver, where each phase center is considered as an element of an array of antennas.
Published in:	Proceedings of the 15th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2002) September 24 - 27, 2002 Oregon Convention Center Portland, OR
Pages:	287 - 288
Cite this article:	Santos, Marcelo C., Farret, Julio C., "Analysis and generalization of a dual-antenna multipath mitigation technique.," Proceedings of the 15th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2002), Portland, OR, September 2002, pp. 287-288.
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