High Rate OFDM Acoustic Link for Underwater Communication

A high bit rate acoustic link over an underwater channel is investigated . Design of a Digital communication system utilizing acoustic signals for underwater applications is a very challenging field due to the extremely complex nature of the underwater channel. The conventional techniques for overcoming the channel effects used in communication systems elsewhere fail to give the desired results when applied in this field of communications. This paper aims at designing one such system, which can effectively withstand the adverse effects of the channel but still provide adequate data rate. For this purpose, an in-depth study of the underwater communication channel was carried out and the findings are analyzed. Orthogonal Frequency Division Multiplexing has been selected as the modulation scheme, deviating from the more conventional single-frequency methods hitherto used in this field in the past. A relatively simple but robust communication system has been designed covering techniques ranging from Communications, Acoustics and Signal Processing. The inherent features of the OFDM scheme make the system rugged against channel effects such as extremely strong multi-path and additive noise. Additional features have been incorporated to make the system immune to Doppler shifts and hardware instabilities. The system has been put through simulated as well as real channel conditions and the results have been presented.