S-Curve Shaping: A New Method for Optimum Discriminator Based Code Multipath Mitigation

The paper characterizes the optimum code multipath mitigation in a GNSS receiver which can be achieved by a linear combination of several correlators or equivalently by correlating the incoming signal with a code-tracking reference- function. After a review of currently used code multipath mitigation techniques, a new technique is developed to determine positions and weights of the correlators (or the shape of the code-tracking-reference-function) in order to achieve the best possible multipath mitigation performance within the chosen framework. It is based on the definition of an ‘optimum’ S-curve. A non-coherent code discriminator is formed by dividing the coherent discriminator by the punctual correlator. The technique is applied to BPSK(1) and BOC(1,1) signals for infinite, 16 MHz and 8 MHz bandwidth. Outside its linear region, the S-curve is slightly offset to avoid false stable tracking points as they occur for BOC signals. It is shown that within this approach high-bandwidth BPSK and BOC signals achieve virtually identically multipath envelopes. The resulting discriminator is implemented and tested in a software receiver.