Optimal combination and reference functions of signal-to-noise measurements for GNSS multipath detection

Multipath is the most limiting factor in many GNSS positioning applications, where it inevitably degrades the attainable precision. Among the different proposals to identify observations affected by multipath, Strode and Groves have recently proposed a method based on the comparison of GPS signal-to-noise (SNR) actual measurements with suitable reference functions previously computed in a low-multipath environment. We have found significant issues with its application to our particular GNSS experiments, however. In particular, we discuss whether the reference functions that are needed to be computed for low-multipath environments after tedious and time consuming field campaigns can be used for a future occasion, or not, as well as the possibility of applying the method to other GNSS global constellations (Galileo and GLONASS). Additionally, we elaborate on an alternative idea consisting in the use of the best combination of SNR measurements for the different signals in the different constellations in order to obtain a multipath estimator that is unbiased, universal and performs better than the use of reference functions.