Spread-Spectrum Techniques for Bio-Friendly Underwater Acoustic Communications

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B. Sherlock, J. A. Neasham and C. C. Tsimenidis, “Spread-Spectrum Techniques for Bio-Friendly Underwater Acoustic Communications,” in IEEE Access, vol. PP, no. 99, pp. 1-1.

doi: 10.1109/ACCESS.2018.2790478

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.

Published Open Access at: http://doi.org/10.1109/ACCESS.2018.2790478



Implementation of a Spread-Spectrum Acoustic Modem on an Android Mobile Device.

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Sherlock, B.; Neasham, J.A.; Tsimenidis, C.C., “Implementation of a Spread-Spectrum Acoustic Modem on an Android Mobile Device” in OCEANS 2017 – Aberdeen , vol., no., pp.1-9, 19-22 June 2017

doi: 10.1109/OCEANSE.2017.8084730

Abstract: Underwater acoustic modems can be expensive and inflexible. Software-defined underwater modems provide flexibility to modify the protocols and modulation schemes. The motivation of this research is towards producing minimal cost, low-power systems. The focus in this paper being the concept of a surface receiver consisting of a hydrophone plugged into a mobile device such as a smart phone or tablet. Applications could be where data or diagnostics are required from a distributed network of underwater sensors in the field that incorporate an integrated acoustic modem. Spread-spectrum signals with large bandwidth-time products are considered including binary orthogonal keying (BOK) using linear frequency modulated (LFM) chirps (Chirp-BOK) and pseudorandom noise m-ary orthogonal code keying (PN M-OCK). Bandwidth of 8 kHz to 16 kHz is utilised for simulated performance of the modulation schemes. The modulation schemes target low-power, low-received-SNR applications with rates between 23.4 bit/s and 375.7 bit/s, targeting a BER of 10-4 at received-SNR of -14 dB to -6 dB respectively. A receiver structure design is implemented on an Android mobile device with experimental validation carried out in a marina over a 100m range. The receiver application was able to successfully demodulate, error-free, all packets received in real-time with received SNR of 34 dB. The receiver modulation scheme was user-selectable at run-time. Recordings from the marina trials were combined with AWGN for varying SNR. These were played into the mobile device for real-time demodulation and showed the mobile device and receiver application produced the target BER of 10-4 for SNRs of -12 dB to 0 dB for the rates 23.4 bit/s and 375.7 bit/s respectively.

Published at: http://doi.org/10.1109/OCEANSE.2017.8084730

Self Archived at: Sherlock-OCEANS2017-Paper-selfhosted



Signal and Receiver Design for Low-Power Acoustic Communications Using M-ary Orthogonal Code Keying.

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Sherlock, B.; Tsimenidis, C.C.; Neasham, J.A., “Signal and receiver design for low-power acoustic communications using m-ary orthogonal code keying,” in OCEANS 2015 – Genova , vol., no., pp.1-10, 18-21 May 2015

doi: 10.1109/OCEANS-Genova.2015.7271500

Abstract: Low-power, low received signal-to-noise-ratio (SNR) signals have potential for reducing the impact on marine life from acoustic communications. Here we explore the use of bandlimited pseudo-noise m-ary orthogonal code keying (M-OCK) scheme using m-sequences. Analysis and simulation of receiver structure for synchronisation and data demodulation performance is carried out. Performance of M-OCK is compared with m-ary quadrature amplitude modulation with direct-sequence spread-spectrum (M-QAM DSSS). Real-world channel experiments are carried out with transmission power for the M-OCK sequences limited to less than 1 W acoustic power (170.8 dB re 1 μPa at 1 m) and transmission range varied from 100 m to 10 km in the North Sea. Synchronisation at 10 km is achieved with effective received signal-to-noise-ratio of less than -9.96 dB, and data demodulation of 140.7 bit/s raw throughput with pre-coding bit-error-rate (BER) 0.5 × 10-1 (symbol-error-rate (SER) 0.1) and 46.9 bit/s raw throughput with pre-coding BER 0.9 × 10-3 (SER 1.95 × 10-3). Error-free synchronisation and data demodulation is achieved at ranges up to 2 km, demonstrating data rates in excess of 140 bit/s.

Published at: http://doi.org/10.1109/OCEANS-Genova.2015.7271500

Self Archived at: Sherlock-OCEANS2015-Paper-selfhosted