Characterization of the effects of high multipath phase rates in GPS

GPS multipath has been studied since the early 1970s. Prior to the investigation described in this paper, however, the effects due to the relative Doppler shift between the direct and multipath signal components have received scant attention. The single previous study that did address the issue indicated coherent receivers had significant performance advantages over noncoherent receivers. Specifically, it was stated that under the condition of fast-fading multipath, noncoherent receivers would yield a bias error, whereas coherent receivers would not. After reviewing the background theory, this paper describes a revised model of the phenomenon and shows the results of hardware simulations which validate the existence of the bias in both receiver types and offer support for the new model. A case study of a specific commercial receiver is presented.