Dependence of Demodulation Performance on Bandwidth for Underwater Acoustic Communication with a Fast Moving Terminal in Shallow Water

Zadoff-Chu (ZC) sequences are widely used for synchronization and uniform Doppler estimation in communication systems. Although ZC sequences offer high correlation peaks for signal detection in underwater acoustic communication (UWAC) under severe Doppler shifts, they may result in inaccurate time synchronization and Doppler estimation, particularly under narrow bandwidth conditions. Such inaccuracies degrade demodulation performance due to timing errors in down-sampling. Adaptive digital down-conversion (ADDC) has been proposed to mitigate errors in down-sampling timing caused by nonuniform Doppler shifts. This study evaluates the performance of ADDC through simulations in shallow water, where a terminal moves at 10 kn. Simulation results show that timing errors caused by ZC sequences degrade demodulation performance in horizontal communication under narrow bandwidth, due to more significant Doppler shifts compared to vertical communication. Furthermore, the results indicate the possibility that ADDC effectively mitigates this degradation, demonstrating its effectiveness in horizontal channels with fast-moving terminals.