Full-duplex, multi-user and parameter reconfigurable underwater acoustic communication modem

Underwater acoustic communication networks are becoming focus of active research due to several oceanographic developments and military applications. Long time delay present in underwater acoustic channel limits data rate of the network. Another major reason for low throughput is that almost all the acoustic modems operate under half-duplex mode. For increasing communication throughput, a full-duplex, multiuser, parameter reconfigurable underwater acoustic modem is presented in this paper. Transmission is done through an omnidirectional transducer and a directional vector sensor is used for reception. Orthogonal frequency-division multiplexing (OFDM) and Code division multiple access (CDMA) with spread spectrum (SS) are used for realizing full-duplex and multi-user acoustic communication. TMS320C6455 DSP and Cortex-A8 ARM are embedded in the modem for real time digital signal processing for the communication scheme. To cater different underwater environment conditions for some special applications, the parameters of OFDM can be modified via acoustic link using robust SS underwater acoustic communication. A cable link directly to the computer for modem parameter reconfiguration is also provided. The proposed modems have been tested in sea trials. The results of these trials indicate that significant improvement in the network throughput rate can be achieved by using above mentioned hardware and techniques.