R&D of a dual mode acoustic modem testbed for shallow water channels

Recent years witnessed an increasing requirement of marine missions like oceanographic investigation, environmental monitoring, underwater structure inspection and sea bottom resource exploitation, which urged the R&D of high performance underwater acoustic (UWA) modems. However, as underwater acoustic channels pose multiple difficulties such as multipath, time-space selectivity, frequency dependent noise, and Doppler shifts on transmission, currently there is not a single modulation strategy that can provide high data rate, energy efficiency and channel robustness simultaneously. Enlightened by the similar dual mode (DM) systems developed in wireless channels, this paper presents the R&D of a DM UWA modem testbed system, which enables the switch between DSSS and OFDM scheme to accommodate different channel situations. Experimental results obtained in a physical shallow water channel demonstrate the effectiveness of the proposed system.