Direct position tracking loop based on linearised signal model for global navigation satellite system receivers

Vehicle positioning with global navigation satellite system in urban environments has three challenges: signal attenuation, multipath and dynamic. In this study, the direct position tracking loop (DPTL) is proposed. Different from non-linear navigation domain vector tracking loops, DPTL is a linear scheme derived from the linearised model of baseband signal. Thus, the computational cost of DPTL is not too expensive. Different from pseudorange-based vector tracking loops (PB-VTLs) taking pseudorange residuals as intermediate variables to synthesise user position residuals, DPTL directly discriminates user position residuals in the domain of user position and receiver clock bias. Thus, DPTL takes full advantage of geometric relationships between the receiver and satellites to improve positioning accuracy. Moreover, for the purpose of improving positioning accuracy and maintaining sufficiently wide dynamic range at the same time, DPTL incorporates the vehicle movement characteristic in urban environments to configure early-late distance spacings of the discriminator and process noise power spectral densities of Kalman filter separately for each component of user position and receiver clock bias. Performance analysis and simulation confirm the tracking and positioning performance of DPTL is better than that of the PB-VTL in both dynamic weak signal and multipath environments.