Covert Underwater Acoustic Communication Using Marine Ambient Noise Without Detectable Features

Learning from steganography, this study considers ocean ambient noise as a carrier and proposes a covert underwater acoustic communication scheme without detectable and repetitive features. We modulate the information in the parameters of the steganography operation rather than the specific signal waveforms. The steganography operation mainly includes three steps: symmetrical division, phase rotation, and time–domain inversion. The rotation phases are related to the transmitted information. The receiver demodulates by performing the same operation, like transmitter without knowing transmitted waveforms. Therefore, we can use countless ocean ambient noise signals to transmit the same information, which can avoid repetitive features. To optimize the communication performance, the relationship between the demodulation output value and the rotation phases is derived, and the optimal modulation parameter setting methods of modulation are given. Finally, the simulation and sea trial results show that the bit error ratio of the studied covert underwater acoustic communication scheme is approximately 5 × 10−4 at a signal-to-noise ratio of −4 dB, which verifies the effectiveness of the scheme, and the rate is 4 bps. And the results of cyclic spectrum, cepstrum and square frequency-doubling methods show that the signal of the studied scheme does not have any detectable features.