Multipath Effects on a GNSS Receiver Tracking Performance

Kurzfassung

Multipath propagation is a major source of error in a GNSS receiver. In particular, the tracking of the time delay estimate, which is used to calculate the distance between the satellite and the user, is affected by multipath in two ways: the estimation of the time delay will get biased and the tracking error jitter is changed. Although the performance degradation due to multipath is usually assessed by means of simulations, here we propose a straightforward mathematical model for it. Under certain assumptions, it is indeed possible to calculate the bias and the variance of the tracking error due to multipath. And this can me done for a propagation channel made of an arbitrary number of paths. With such a model, the effect of multipath can be described in terms of MSE of the tracking error, which, instead of being obtained through simulations can be obtained by mathematical analysis. The MSE,infact, turns out to be a deterministic function of the channel impulse response and of the receiver parameters. This approach in the characterization of multipath adds a new useful tool in the evaluation of performance of GNSS receiver, since not only can save resources which are needed to do field measurements, but it has the added value of providing an insight of the role of each parameter in what it is overally called “multipath error”. Analytical results will be presented for a static multipath scenario, and multipath mitigation techniques, as the Narrow Correlator and the Double Delta Correlator, thought with the intention of reducing the multipath bias, will be analysed and compared from this new perspective.