Multipath parameter estimation using GNSS receiver Doppler measurements

Abstract

The accuracy and robustness of global navigation satellite systems (GNSS) degrade in urban environments, which particularly affects low-cost GNSS users. Among various multipath mitigation techniques, signal parameter estimation enables the identification and characterization of interference, facilitating its removal from the navigation solution. This study models multipath interference in the receiver's frequency-locked loop (FLL) to characterize Doppler measurement errors induced by multipath. Subsequently, a Doppler-based multipath parameter estimation method is proposed using a nonlinear least squares (NLS) algorithm to estimate the Doppler frequency, carrier phase, and signal strength of both line-of-sight (LOS) and reflected signals. Experiments were conducted in urban areas of Hong Kong, with ray-tracing techniques utilizing ground-truth data as a benchmark for assessing multipath detection and parameter estimation accuracy. The proposed method is also compared with established signal quality monitoring (SQM) metrics and the multipath estimating delay-locked loop (MEDLL) technique. Results demonstrate that the Doppler-based approach enhances multipath detection efficiency, reduces false alarm rates, and provides more reliable parameter estimation, particularly in dynamic user scenarios.