Evaluation & Reduction of Multipath-Induced Bias on GPS Time-of-Arrival
November 2001
Ronald L. Fante, The MITRE Corporation
John J. Vaccaro, The MITRE Corporation
ABSTRACT
This paper presents new expressions for the bias error and variance introduced by multipath onto the time of arrival estimate obtained using a non-coherent early-late gate discriminator. The results include the effect of front-end bandwidth and early-late gate spacing.
We also investigate a blind method for cancelling the multipath, in order to improve the time-of-arrival estimate. Our approach uses early-late gate processing on an objective function derived from an adaptive FIR filter that attempts to match the crosscorrelation of the received signal with a multipath-free replica of the desired crosscorrelation. This method performs reasonably well, and decreases the bias by approximately a factor of 2, even in very stressing multipath environments.
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