Application of Virtual Time-Reversal and Pulse Position Modulation for Underwater Acoustic Communication in Dynamic Shallow-Water Environments

The challenges of underwater acoustic communication in shallow water environments are dominated by severe multipath propagation and dynamic channel variations, resulting in intersymbol interference (ISI) and Doppler shifts from mobile platforms. This paper introduces an innovative communication architecture that combines three key techniques: pulse position modulation (PPM), multi-Doppler matched filtering, and virtual time-reversal (VTR). The system's cornerstone is a novel block-wise VTR approach that adaptively responds to channel variations while maintaining signal clarity. Initial system validation through water tank experiments demonstrated successful signal processing and hardware implementation under controlled conditions. The system's reliability was further verified through simulations incorporating real field environments and actual seafloor topography. Experimental results showed successful decoding of all test transmissions, while simulations confirmed robust performance under complex channel conditions. Field experiments are planned to evaluate system performance in dynamic ocean environments, where mobile platforms and varying oceanographic conditions present additional challenges. Our integrated approach presents a significant advancement in reliable underwater communication for complex nearshore environments, with potential applications in marine research, ocean exploration, and autonomous underwater vehicle operations.