Multipath Effects on GPS Code Phase Measurements

Abstract

An analysis of multipath errors in GPS code phase measurements is presented, assuming the code phase is measured with the widely used noncoherent delay lock loop. Both specular and diffuse reflections are considered. A rough estimate for the fading bandwidth is given for mobile and stationary users, showing that averaging is far more effective for mobile than for stationary users. In general, however, a certain mean range error is present for both stationary and mobile users, depending on the power‐delay profile of the received signal. Measurements near buildings confirm the asymmetry of multipath errors, which causes the nonzero mean, and show that range errors can take values of more than 100 m.

Characterization of the effects of high multipath phase rates in GPS

“…A noncoherent DLL (NCDLL) purposefully performs nonlinear operations to ensure robustness against phase uncertainty in the received signal and thus is widely used in GPS receiver-tracking schemes. It has been shown in the literature (Van Nee 1991, 1993, 1995 that this nonlinearity leads to a measurement bias in cases where signals are corrupted by high-frequency fading multipath such that the composite signal cannot be perfectly tracked by the receiver. The goal of the tracking process in the DLL is to maintain synchronization between the incoming GPS transmission and a locally generated replica of that signal so that an estimate of signal propagation time can be made.…”

“…This paper concerns itself specifically with the latter since an abundance of theory and validation data (Braasch 1992;Cox et al 1999;Braasch and DiBenedetto 2001) has been produced for the static and low-dynamics cases. Work in the analysis of highdynamic multipath has produced mathematical descriptions of discriminator functions for general cases of multipath-corrupted signals in coherent and noncoherent delay lock loops (Van Nee 1991, 1993, 1995.…”

“…Guaranteeing system reliability to the degree dictated by governing entities requires a rigorous exploration of multipath modeling and mitigation techniques. Numerous books and articles have been published which attempt to characterize the effects of multipath in GPS, including theoretical studies of the dynamic characteristics of multipath examined more deeply in this article (Van Nee 1991, 1993, 1995Kelly and Braasch 1999), analysis of tracking mechanisms in static multipath scenarios (Kaplan 1996;Parkinson and Spilker 1996;Misra and Enge 2001), and validation data for static cases (Brasch 1992;Braasch and DiBenedetto 2001;Cox et al 1999). Most current multipath models, and all published validation efforts regarding multipath error, are concerned with bounding such error by defining the envelope of the worst-case performance based on characteristics of the composite incident signal.…”

GNSS Code and Carrier Tracking in the Presence of Multipath

“…The = k 3 I e − I l I e + I l (3) tracking loops accurately follow satellite-user dynamics, atmospheric and clock effects. However, in the presence of a secondary signal, these loops…”

Multipath Propagation, Characterization and Modeling in GNSS

“…However, the variability of the ionospheric conditions may create additional range biases when smoothing. Van Nee in [19] showed that due to the non-zero mean of code-phase multipath, multipath effects cannot be eliminated by simply averaging over longer periods.…”