Abstract
Underwater acoustic (UWA) biomimicking communications have been developed for covert communications. For the UWA covert communications, it is difficult to achieve the bit error rate (BER) and the degree of mimic (DoM) performances at the same time. This paper proposes a biomimicking covert communication method to increase both BER and DoM (degree of mimic) performances based on the Time Frequency Shift Keying (TFSK). To increase DoM and BER performances, the orthogonality requirements of the time- and frequency-shifting units of the TFSK are theoretically derived, and the whistles are multiplied by the sequence with a large correlation. Two-step DoM assessments are also developed for the long-term whistle signals. Computer simulations and practical lake and ocean experiments demonstrate that the proposed method increases the DoM by 35% and attains a zero BER at −6 dB of Signal to Noise Ratio (SNR).
Highlights
The conventional Underwater acoustic (UWA) covert communication schemes achieve the covertness using the spread spectrum that spreads out the communication signal over a wide frequency band, which is considered as background noise [1,2,3,4,5,6,7]
The short division of the whistle increased the frequency bandwidth of the whistle pattern, which decreased the degree of mimic (DoM) and Bit Error Ratio (BER) performances
The computer simulation and the ocean experiments were executed to show that the proposed method demonstrated better DoM and bit error rate (BER) performances than the conventional convert communications
Summary
Biomimetic communications have been developed, which mimic the dolphin whistles to increase the covertness [8,9,10,11,12,13]. The short division of the whistle increased the frequency bandwidth of the whistle pattern, which decreased the degree of mimic (DoM) and Bit Error Ratio (BER) performances. To increase the DoM and BER performances, the time-frequency shift keying (TFSK) method was researched [13]. The BER performance of the TFSK varied with the transmitted whistle patterns, and the time- and frequency-shifting units that satisfy the orthogonality in the time- and frequency-domains were not derived.
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