Characterization of the effects of high multipath phase rates in GPS

Abstract

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.

A Ray-Tracing Technique to Characterize GPS Multipath in the Frequency Domain

“…As shown, depending upon PRN location, Δ could be zero in which case it is not possible to distinguish between direct and reflected signals in the frequency domain. The occurrence of zero Δ which manifests itself as a constant bias in the pseudorange measurements, even in the case of very long coherent processing, was proven by Kelly et al [31].…”

Characterization of multipath phase rates in different multipath environments

“…Kelly and Braasch 1999, 2000, 2001Kelly et al 2003;Irsigler 2008). They also determine to which degree multipath influences can be mitigated, e.g.…”

Earth-Surface Multipath Detection and Error Modeling for Aircraft GPS Receivers

“…The fading frequency is the difference between the carrier frequencies of the LOS signal and the reflected signal, which is a function of the vertical velocity of the aircraft [10]. Simulation and bench test results in [13] show that for both coherent and non-coherent discriminators, a substantial pseudorange bias can be observed at high fading frequencies of a few tens of Hz.…”

“…On the other hand, as an aircraft flies over relatively smooth terrain or water surfaces at a constant descent rate, which is the case during an aircraft precision approach, the reflection would be strong and steady, its path delay would gradually decrease, and the fading frequency would remain stable during this time. According to the model in [13], it is possible to induce biases in the pseudorange measurements that could degrade the accuracy of the precision approach operation. To satisfy precision approach accuracy and integrity requirements, it is crucial to know how large these errors can become and whether or not there is room for them in the error budget.…”