Clean-to-Composite Bound Ratio: A Multipath Criterion for GNSS Signal Design and Analysis

Multipath is one of the most challenging propagation conditions affecting global navigation satellite systems (GNSS), which must be mitigated in order to obtain reliable navigation information. In any case, the random multipath nature makes it difficult to anticipate and overcome. Therefore, for legacy GNSS signal performance assessment, modern GNSS signal design, and future GNSS-based applications, robustness to multipath is a fundamental criterion. Different multipath metrics exist in the literature, such as the MPEE, usually leading to analyses only valid for a dedicated receiver/signal combination and only providing information on the bias. This article presents a general criterion to characterize the multipath robustness of a generic band-limited signal (e.g., GNSS or radar), considering the joint delay-Doppler and phase estimation. This criterion is based on the Cramér–Rao bound, which makes it universal, regardless of the receiver architecture and the signal under analysis, and provides information on the actual achievable performance in terms of estimated time-delay (i.e., pseudorange) and Doppler frequency variances.