Bionic Covert Underwater Acoustic Communication Based on Time–Frequency Contour of Bottlenose Dolphin Whistle

Abstract

In order to meet the requirements of communication security and concealment, as well as to protect marine life, bionic covert communication has become a hot research topic for underwater acoustic communication (UAC). In this paper, we propose a bionic covert UAC (BC-UAC) method based on the time–frequency contour (TFC) of the bottlenose dolphin whistle, which can overcome the safety problem of traditional low signal–noise ratio (SNR) covert communication and make the detected communication signal be excluded as marine biological noise. In the proposed BC-UAC method, the TFC of the bottlenose dolphin whistle is segmented to improve the transmission rate. Two BC-UAC schemes based on the segmented TFC of the whistle, the BC-UAC scheme using the whistle signal with time-delay (BC-UAC-TD) and the BC-UAC scheme using the whistle signal with frequency-shift (BC-UAC-FS), are addressed. The original whistle signal is used as a synchronization signal. Moreover, the virtual time reversal mirror (VTRM) technique is adopted to equalize the channel for mitigating the multipath effect. The performance of the proposed BC-UAC method, in terms of the Pearson correlation coefficient (PCC) and bit error rate (BER), is evaluated under simulated and measured underwater channels. Numerical results show that the proposed BC-UAC method performs well on covertness and reliability. Furthermore, the covertness of the bionic modulated signal in BC-UAC-TD is better than that of BC-UAC-FS, although the reliability of BC-UAC-FS is better than that of BC-UAC-TD.

Recognition of Whistle-like Signals Based on FM Harmonic Characteristics

“…Further, the whistle-like signal is an FM harmonic signal with the strongest energy at the fundamental frequency energy [10], thus the frequency with the largest energy in each segment is taken as the fundamental frequency of the segment, and the fundamental frequency signal timefrequency contour (TFC) can be expressed as…”

“…After the above fundamental TFC is found, the harmonic TFC which is the frequency multiplication of the fundamental frequency point at each time segmentation is expressed as 1 ( ), ( ) () , ( ) (10) where fi represents the TFC of the i-th order harmonic signal.…”

Acoustic projectors make covert bioacoustic chirplet signals discoverable

“…One additional acoustic preamble enables synchronization and channel estimation based on the matching pursuit algorithm. A recent contribution by Xie et al 13 proposes to smooth the time-frequency contour of bottlenose dolphin vocalizations, and to subdivide them into segments. Information is then modulated into each segment via a frequency shift in the corresponding spectrogram.…”

“…Our work informs biomimicking system design based on engineered as well as played-back animal sounds by evaluating how the emitted signals really resemble natural sounds. In fact, time-based signal modulations 10 , 17 , 19 , frequency-based modulations 9 , 13 , and even direct playback 12 , 16 can be put in jeopardy if the last element of the transmitter chain (i.e., the transducer) exposes the emitted signal as a non-natural one.…”

Entropy and Information Theory in Acoustics

“…In order to improve the communication rate of existing bionic concealed-hydroacoustic communication (BC-UAC) and improve the concealment and effectiveness of the constructed bionic communication signal, Xie et al proposed a bionic covert UAC method based on the time–frequency contour of the bottlenose dolphin whistle, which can overcome the security problems of traditional low-signal–noise-ratio covert communication and exclude detected communication signals such as marine biological noise [ 4 ]. The performance of the proposed BC-UAC method, in terms of the Pearson correlation coefficient and bit error rate, is verified under simulated and measured underwater channels.…”