GNSS Multifrequency Receivers in Urban Environment: Theoretical Analysis

摘要

In this paper, a theoretical approach for the analysis of synchronization performances in GNSS receivers adapted to reduce errors, especially caused by multipath fading, in a urban environment is proposed. In particular, two kinds of bi-frequency receivers based on data fusion methods are analyzed. The performances have been evaluated by comparison of simulated results in a real case and theoretical values based on the dispersion of the S-curve, the characteristic curve output of the DLL. One way to cope with multipath effects is equipping receivers with software modules able to reduce multipath effects. This paper explains two different methods based on data fusion and in particular on fusion between different frequencies. It is shown that improvement is possible if and when the multipath can be considered independent for two frequencies properly spaced in the frequency domain. A theoretical analysis has been carried on together with computer simulation. The signal channel model has been developed with Galileo in mind to show how data fusion techniques can be applied exploiting the frequency diversity. The receiver modules taken into account are the Equal Gain Combining (EGC) and the Adaptive Gain Combining (AGC). Starting from the statistical model of a classical DLL code-tracking system, a theoretical model for both EGC and AGC is derived. To verify the correctness of the theoretical model, a simulation environment has been set up, with the possibility of varying different parameters. The multipath model is referred to an urban environment. Resells are shown both for EGC and AGC receivers. Correct decision probability in the considered cases has confirmed the results in the simulated cases.