Covert underwater acoustic communication using whale noise masking on DSSS signal

Abstract

A biological mimicry method for covert underwater acoustic communication (UAC) is presented. This is useful in clandestine communication where the contents of transmission and/or location of transmitter are required to be concealed. In this scheme, direct sequence spread spectrum (DSSS) signal which carries information is masked underneath a relatively louder whale sound in time and frequency domain. Instead of reducing signal level to a minimum, the masked communication signal is allowed to be detected but it could easily be excluded in the process of recognition/classification by an adversary. This is because the received signal resembles sounds emitted by whales and the information signal is masked by the loud whale noise. The designed communication frame structure for this scheme and coherent interference cancelation method for separation of whale sound and DSSS signal is also given. A virtual time reversal mirror (VTRM) equalization method is adopted for focusing energy of DSSS signal while accurate channel estimation is realized by the high SNR whale sound using matching pursuit (MP) technique. The effectiveness of the proposed scheme has been presented by the results of simulations.