The Multipath Invariance Approach for Code Multipath Mitigation

The concept of multipath invariance asserts that there exist properties and/or regions of the code correlation function that do not change as a function of the multipath amplitude, delay, phase and phase rate. These Multipath Invariant (MPI) points exist at the plateaus of the correlation function. Previous experiments have demonstrated that despite low correlation power, it is possible to implement the Tracking Error Compensator (TrEC) algorithm, which uses these MPI points to mitigate multipath. In addition, it has been previously asserted that TrEC not adversely affected by finite frontend bandwidth considerations and is potentially very useful for mitigating multipath in extremely narrowband receivers. To evaluate the performance of the MPI approach, the TrEC algorithm was implemented in a narrowband receiver. Using code double-differences over a short baseline between two rooftop antennas, real-time position errors were recorded using live satellites. Three different multipath scenarios were tested. The results were compared with and without multipath compensation and also with and without carrier smoothing applied to the pseudoranges. For the last case—a large multipath scenario—(wideband) narrow correlator receiver performance was compared to (narrowband) TrEC performance. Significant reductions in multipath errors were attained through using this novel approach. Specifically, in all cases TrEC was significantly more effective at reducing the mean bias errors due to multipath than the other techniques.