Evaluation & Reduction of Multipath-Induced Bias on GPS Time-of-Arrival

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.