Abstract: Purpose/Objective: This work investigates techniques to mitigate the impact of acoustic communication signals on marine life, by minimising source level (SL) and designing waveforms with characteristics proven to reduce animal discomfort in bioacoustics studies. Methods: High-ratio spread spectrum transmission is employed with bandwidth-time products exceeding 1000. Signalling is based on families of near orthogonal pseudo-noise waveforms, generated by bandpass filtering of binary M-sequences. This enables reception of data, at very low SNR, over a radius many times greater than the radius of discomfort experienced by marine mammals. Computationally efficient receivers with novel synchronisation structures needed to be developed to operate at very low SNR and with severe Doppler effects. Results: Simulations show the proposed scheme is able to achieve 45 bit/s at –18dB SNR and 140 bit/s at –12dB SNR. Experimental system performance was assessed during realistic experiments in the North Sea, verifying performance over ranges up to 10km with transmitted SL of <170dB re 1 μPa @ 1m and with Doppler effects induced by relative motion exceeding 2m/s. Conclusion: The system developed compares favourably, in terms of SNR performance and channel utilisation, with previously reported work aimed at covert communication but offers reduced transmitter/receiver complexity and discomfort to animals. Significance: The work offers a way forward to more bio-friendly acoustic modem devices for operation in regions with sensitive fauna and/or increasingly strict environmental controls.
Cite: B. Sherlock, J. A. Neasham and C. C. Tsimenidis, “Spread-Spectrum Techniques for Bio-Friendly Underwater Acoustic Communications,” in IEEE Access, vol. 6, pp. 4506-4520, 2018.
Published Open Access at: http://doi.org/10.1109/ACCESS.2018.2790478