This paper proposes a novel modulation scheme
for underwater acoustic communications based on chaotic signal. The proposed method is Chaotic Direct-sequence spread spectrum (DSSS). The conventional modulation techniques often encounter challenges
related to spectral efficiency,
robustness against noise, and security. In contrast, chaotic modulation harnesses the unique properties of chaotic signals to achieve improved performance in these aspects. In this study, the Logistic map is used as the spreading sequence code for BPSK signal for
turbid water and the significant attenuation of electromagnetic (EM) waves. Nevertheless, acoustic communications, despite their
direct sequence spread spectrum
communications. In contrast to conventional methods employing chirp signals
for synchronization, this approach utilizes a chaotic signal to achieve
synchronization. Additionally, demodulator incorporates a Doppler shift compensator capable of
addressing shifts of up to 10 m/s. This compensator operates on a bank of Doppler shifts. To assess the impact of the underwater acoustic channel on
our proposed acoustic signal, the simulations in MATLAB were conducted. The channel was characterized by the inclusion of white Gaussian noise, multipath propagation and the Doppler effect.