Impact of Replica Matching on Distortion-Optimized Multilevel Coded Spreading Signals

Abstract

Modern radio navigation satellite systems (RNSS) support a variety of positioning, navigation and timing (PNT) applications, yet advanced users increasingly demand greater accuracy, robustness, and integrity. Although multi-frequency multi-constellation (MFMC) processing and correction products largely mitigate ionospheric and orbit/clock errors, interference, multipath (MP) propagation, and signal deformation remain major sources of ranging error. This study investigates whether multilevel coded spreading symbol (MCS) signals, which are designed to outperform conventional binary offset carrier (BOC) signals by mitigating modeling mismatch due to distortion, can achieve these improvements. Distortion-optimized MCS candidates, derived under relevant constraints, are evaluated across receivers employing either waveform-matched MCS replicas or simplified 1-bit binary coded spreading symbol (BCS) replicas. Additionally, the performance of realistic receiver front-ends, which were not considered during signal optimization, is compared to the reference front-end used in the optimization. The results show that these signals maintain superior MP suppression compared to higher-order BOCs and exhibit low tracking jitter under distortion. However, intermediate Pareto solutions incur the largest correlation losses (up to 1.28 dB), emphasizing the need for careful selection when targeting legacy or low-complexity receivers. Overall, the findings support distortion-optimized MCS signals as robust candidates for next-generation RNSS.