Experimental assessment of a direct sequence spread spectrum underwater acoustic communication method

Abstract

This paper describes the analysis of spread spectrum acoustic data for underwater point to point communication acquired during seatrials carried out in shallow water areas. The signals transmitted are modulated using a PSK direct sequence spread spectrum approach, employing differentially coherent modulation. The use of Gold pseudo noise sequences allows one to achieve private communication. On the receiver side, a rake receiver is used to positively exploit the energy present in multiple propagation paths. Moreover, a preliminary step of synchronization and parameter estimation necessary for Doppler compensation is performed together with a tracking procedure that allows an adaptation to the instantaneous Doppler shift. The analysis of real data received by a vertical array shows that the developed communication algorithm is capable to handle the multipath phenomenon and the variabilities typical of a shallow water channel, allowing one to achieve good performances at a bit rate of about 130 bit/s. In particular, in a shallow water channel (50 m deep) with ranges up to 1 km, the system is able to obtain zero errors if in reception more than one signal received by the vertical array is taken into account. © 2012 Acoustical Society of America.