Experimental demonstration of differential OFDM underwater acoustic communication with acoustic vector sensor

A new Orthogonal Frequency Division Multiplexing (OFDM) based underwater acoustic communication scheme utilizing acoustic vector sensor is presented. The acoustic channel assumed has the slow time-varying characteristic and the neighboring signals can be considered as transmitted through the same channel. The differential modulation encodes information through the relative phase changes between adjacent subcarriers. Therefore, instead of adding pilots to monitor the channel, the differential demodulation is used to reconstructs transmitted information without necessity of channel estimation. This increases the transmission rate and reduce the complexity of processor at the receiver. An acoustic vector sensor is used in the differential OFDM system to further improve the performance of the system with 4.8 dB gains that can be obtained by combined processing pressure and velocity signals from the acoustic vector sensor. To validate the capability of the proposed scheme, an experiment with picture and voice source information was conducted in a lake. The results obtained at different distances demonstrate the proposed system offers a significant advantage.