| A detailed study of a novel method for high-speed acoustic communications in ports and shallow water is presented. A series of field experiments, coupled with simulated results using an acoustic channel model have been conducted to outline the optimal modulation schemes for use in the highly reverberant and Doppler dominated shallow water acoustic channel. Field experiments were conducted in the vicinity of the SeaTech marina and the Port Everglades turning basin in water depths of 2 to 15 meters and ranges of between 25 and 75 meters. An automated FAU acoustic modem transmitted BPSK and QPSK modulated messages centered at 300 kHz, with a source level of 173 dB re 1muPa and a symbol bandwidth of 25, 50 or 75 kHz. The coded rate varied from 25000 to 150000 bits per second. These high data rates are made possible using a high resolution Decision Feedback Equalizer with an efficient Doppler compensation process. The results of this study demonstrate the ability of such a system to transmit video images in a shallow water environment. |
