Orthogonal frequency division multiplexing cyclic shift keying spread spectrum camouflaging underwater acoustic communication with dolphin whistles as information carrier

A camouflaging modulation method is proposed. The original whistle is represented as orthogonal frequency division multiplexing (OFDM) blocks by using DFT coefficients. The m-sequence is used to modulate the subcarriers of OFDM signal by using the orthogonal frequency division multiplexing cyclic shift keying (OFDM-CSK) spread spectrum technology. The PEAQ algorithm is used to compute the similarity in auditory aspects and the correlation coefficient is used to compute the similarity in waveform, which are as two metrics to evaluate the camouflaging effect. In addition, a self-synchronization method that combines the correlation and OMP algorithm is proposed and hence the frame structure of transmitted signal could be designed as same as the origin whistles, which would improve the camouflaging performance. The bandwidth efficiency of the system is improved by using CSK spread spectrum technology and the robustness of the system is improved by using the vertical time reversal equalization technique. The experiment results verify the feasibility of the proposed camouflaging communication method