Modeling and Validation of GNSS Multipath-Induced Doppler Tracking Error

Multipath interference in urban areas is one of the main reasons for the unreliability of global navigation satellite system (GNSS) navigation and presents a formidable challenge for multipath mitigation due to the inherent unpredictability of reflected signals. Signals reflected from building surfaces, especially in receiver-dynamic applications, can undergo significant Doppler differences compared to the direct signal. Consequently, in the receiver frequency-locked loop (FLL), the tracking of the correct frequency point becomes susceptible to distortion, leading to errors in the receiver measurements. The Doppler frequency is a pivotal parameter for signal synchronization within the receiver and directly shaping receiver velocimetry. Therefore, this paper is dedicated to an in-depth exploration of carrier tracking mechanisms, delving into the derivation of receiver-estimated Doppler with consideration for multiple signal rays. The real-world experiments are conducted to visualize the realistic Doppler estimation error in multipath scenarios. The proposed FLL algorithm shows how signal power, signal ray geometry, and user dynamics influence receiver Doppler estimation over continuous tracking periods. The results indicate increased Doppler estimation errors with higher reflected signal power and a more substantial Doppler difference between the direct and reflected signals.