Characterization and mitigation of urban GNSS multipath effects on smartphones

In urban environments, the code measurements of Global Navigation Satellite System (GNSS) on smartphones can be significantly degraded by presence of multipath and non-Line-Of-Sight (NLOS) effects. Extensive studies have been carried out on characterizing the quality of GNSS code measurements under different conditions, which can be used to refine the weighting model and fault detection method. However, our knowledge regarding the impacts of multipath effects on smartphones remains limited. This includes determining the dominant error source for urban GNSS on smartphones between multipath and NLOS errors, and characterizing the fault-free code measurements for pedestrians in urban canyons. To address these issues, we conducted extensive tests in a typical urban area in Hong Kong and analyzed characteristics of multipath effects. Analysis revealed that 92.5 % of code outliers stem from NLOS signals, which result in longer ranging measurements, making NLOS the dominant error source impacting GNSS performance. Further, we established that over 92 % of fault-free signals are from the opposite sky of a pedestrian, and we found that the sidewalk can be reliably determined by examining signal-to-noise ratio (SNR) measurements, eliminating the need of complex 3D building models. The identified sidewalk can be used to enhance GNSS performance in urban areas. An experiment in the urban canyon was performed in urban canyons. Results show that the accuracy can be improved from 15 m to 4.6 m when the correct sidewalk can be identified.