Multipath Mitigation for Narrowband Receivers

Narrowband receivers are more robust to narrowband interference and to GPS signal faults, but they tend to have relatively poor multipath performance. Few current techniques are capable of mitigating multipath in these receivers. The Tracking Error Compensator (TrEC) however operates independent of the receiver’s precorrelation bandwidth (PCB) using the concept of Multipath Invariance (MPI). Theoretical bandlimited mitigation performance curves for this approach were generated and compared to those of a conventional delay-lock loop. The effects of a narrow PCB on the TrEC were experimentally investigated. A practical TrEC algorithm was developed and implemented on a Mitel Semiconductor receiver having a 2MHz PCB. The performance curves and accompanying statistics were validated for short-delay multipath using a GPS signal generator to generate multipath with known characteristics on a prescribed pseudorange. Measured pseudorange errors were compared to those estimated by the TrEC in real-time. For the same case, position errors resulting from short and long time-constant carrier smoothing and were contrasted with those from the TrEC algorithm. This data suggests that it may be possible to significantly improve the multipath mitigation performance of narrowband receivers.