Biologically inspired covert underwater acoustic communication by mimicking dolphin whistles

Focusing on the need of covert underwater acoustic communication, a camouflage underwater acoustic communication approach is proposed in this paper. The idea is to deceive the interceptor to actively exclude the communication signal as it resembles the original whistle. Based on the time and frequency modulation feature of dolphin whistles, a series of segmented chirp rate modulated signals are designed to mimic the dolphin whistles by sound characteristics. A specialized communication frame structure is designed to facilitate the information demodulation, where the original whistle is used as the synchronization signal and the mimicry signal is followed to convey information. Besides, the original synchronization whistle is also used as a transmit reference to extract the whistle contour and furthermore to get the center frequency of each chirp. Virtual time reversal mirror technique is employed to mitigate channel effect. Fractional Fourier Transform and correlation approaches are adopted to realize demodulation respectively. The feasibility and efficiency of the proposed method are verified by both simulation and sea experiment. Bit error rate less than 10-3 with chirp duration of 20 ms at a distance of 5.5 km is achieved in the sea trial.