Hardware-in-the-Loop Evaluation of Tracking Performance for Distortion-Optimized Multilevel Coded Spreading Signals

Future radio-navigation satellite services (RNSSs) expected to meet tougher spectral separation constraints and to improve positioning, navigation and timing (PNT) performance for users with respect to the current status quo while being subject to inherent distortion along the signal propagation, which motivates the development of distortion-aware-optimized (DAO) signals. Previous simulation-based studies have shown that DAO multilevel coded spreading symbol (MCS) signals can outperform conventional modulations, including binary phase-shift keying (BPSK), binary offset carrier (BOC), and Gabor bandwidth-optimized (GBO) MCS. However, the practical performance of these optimized signals under realistic hardware conditions has not yet been sufficiently validated. This work presents a hardware-in-the-loop (HIL) evaluation of five DAO MCS signal candidates and a BPSK(10) serving as the reference using a HIL experimental setup comprised of two software-defined radios (SDRs). Digitally generated signals are transmitted and recorded over the HIL setup for different transmit power levels and subsequently processed using a configurable software receiver. Performance is evaluated in terms of carrier-to-noise density ratio (C/N0) and empirical code tracking jitter using both a legacy BPSK(10) replica and waveform-matched high-rate MCS replicas. The experimental results demonstrate measurable performance improvements of optimized MCS signals over the BPSK(10) reference. Furthermore, waveform-matched tracking increases the estimated C/N0, particularly for signal candidates exhibiting polarity changes within the chip waveform that introduce correlation losses with conventional BPSK replicas. For the presented case study, the third signal candidate exhibited for both investigated replica types a reduction in code tracking jitter with respect to the BPSK(10) reference.