Characterization and mitigation of multipath fading on multi-frequency GNSS signals in urban environment

Abstract

The global navigation satellite systems (GNSS) receiver is likely to experience performance degradation in the presence of multipath interferences in indoor and urban canyon environments. There will be multiple reflected signals arriving at the receiver antenna from different paths and directions regarding the different locations of the nearby constructions, causing significant fluctuations and distortions on the amplitude and phase of the direct signals. This is the so-called multipath fading effects and usually exhibit with the random features of temporal, spatial, and frequency diversity across the signal bands. To have a better understanding of the multipath fading effects, a live test was conducted near Lujiazui CBD area in Shanghai. The collected data were processed to characterize the signal attenuations and phase fluctuations on multi-frequency GNSS signals via the detrend code delay, carrier phase, and navigation bit errors. The resulting scintillation index on amplitude, code delay, and carrier phase, e.g., S₄, ${\sigma }_{\varphi }$ and ${\sigma }_{\tau }$ can be calculated. Based on these multipath features, the inter-frequency aiding strategy will be utilized for the multipath mitigations in the multi-frequency tracking loop design. The results demonstrate the effectiveness of the multi-frequency tracking algorithm in the urban environment.