Mimicking dolphin whistles with continuously varying carrier frequency modulation for covert underwater acoustic communication

Abstract

This paper proposes a covert underwater acoustic communication scheme to mimic dolphin whistles by continuously varying the carrier frequency and by using antipodal symbol modulation. The continuously varying carrier frequency precisely mimics dolphin whistles, while the conventional method utilizes discrete carrier-frequencies. The antipodal symbol modulation increases bit error rate (BER) performance by a larger Euclidean distance between symbols than conventional chirp spread spectrum (CSS). BER performance was tested by computer simulations and practical ocean experiments, and the degree of mimic (DoM) was evaluated by correlation coefficients and the mean opinion score (MOS) test. BER of the proposed method attains about a 3 dB SNR gain compared with that of conventional CSS, and the DoM of the proposed scheme demonstrates a larger correlation coefficient and a 39% greater MOS score than that of conventional CSS.