Multipath-Aware Carrier Tracking Loop For High Dynamics Real-Time Gnss Receivers

One usual assumption in the high-dynamics GNSS tracking literature is that the GNSS signal is received without multipath. A lot of research has been conducted to mitigate the adverse multipath effects in GNSS receivers, but addressed mainly at the code tracking stage and considering static multipath models. However, in dynamic environments the nature of multipath is substantially different since the Doppler affecting each path can be different, and this can severely affect not only code but carrier tracking. In this work, a post-correlation GNSS signal model is presented to account for the dynamic multipath scenario characterized by a receiver acceleration step, i.e. a linearly changing Doppler frequency. The proposed signal model allows to easily analyze tracking loop behavior in an early design stage and therefore to predict the tracking loop performance with and without multipath presence. This model also shows that the perturbation produced by multipath during an acceleration step has a chirp-like behavior, a fact that can be used to design more robust carrier tracking schemes. In particular, a novel approach based on an additional non-linear filtering stage inside the loop able to mitigate this perturbation is presented and characterized by means of Monte Carlo simulations.