Basic Study of Orthogonal Signal Division Multiplexing for Underwater Acoustic Communication: A Comparative Study

Abstract

Underwater acoustic (UWA) communication in shallow water has been challenging owing to multipath-induced signal distortion and motion-induced Doppler distortion. In this study, we investigate the performance of a UWA communication system using orthogonal signal division multiplexing (OSDM) on intersymbol interference (ISI) and Doppler shift in a simulation, by comparing it with an existing communication system that uses coherent modulation with an adaptive filter, to clarify whether OSDM is suitable for UWA communication in shallow water. The obtained results clarify that OSDM is robust to heavy ISI, and it is expected to be suitable for a rapidly time-varying channel. For example, OSDM can improve the output signal-to-noise ratio (SNR) of 9.4 dB in a shallow water channel with a multipath delay time dispersion of 20 symbols, compared with the UWA communication system with decision feedback equalizer (DFE). However, it is also clarified that OSDM is more sensitive to the Doppler effect compared with the existing communication system, and there is the necessity of applying frequency-offset compensation, because the permissible Doppler shift, when the output SNR falls to -3 dB, for OSDM is less than half that for the UWA communication system with DFE.