Communications and High-Precision Positioning (CHP2): Cycle Slip Trellis Trimming Algorithm

Limited spectral resources and increasing demand for diverse RF applications limit the capabilities of modern RF systems. Recent results in the field of RF Convergence demonstrate that these limitations may be overcome by adopting co-operative and co-design techniques. We designed the Communications and High-Precision Positioning (CHP2) system to provide positioning, navigation, and timing (PNT) and communications services in congested environments with limited spectral access. This system leverages modern two-way ranging (TWR) techniques to provide sub-centimeter ranging precision to flying ad hoc networks (FANETs) in GPS denied environments with only 10 MHz bandwidth. In this study, we extend the CHP2 TWR algorithm to improve robustness against carrier-phase range ambiguities, commonly referred to as 'cycle slips'. We propose a resolution method in conjunction with joint distributed coherence and time-of-flight (ToF) tracking to mitigate these ambiguities, with a structure similar to a time-sensitive Viterbi trellis. The proposed 'trellis trimming' method measures the likelihood of multiple ranging hypotheses and eliminates paths of least likeliness using Bayesian filters. We demonstrate that this method reduces the probability of incorrectly choosing range ambiguities and significantly improves ranging performance in low-SNR regimes where cycle slips are common.