Benjamin Sherlock

Event-driven Underwater Acoustic Sensor Networks (UASNs) face the critical challenge of minimizing event-reporting delay while maintaining energy efficiency in resource-constrained underwater environments. This paper presents a novel asynchronous duty-cycling communication protocol integrating anycast forwarding and collision avoidance mechanisms to address this challenge without requiring energy-intensive synchronization overhead. The proposed protocol enables nodes to perform independent sleep-wake scheduling while opportunistically leveraging multiple forwarding candidates to minimize transmission latency. To handle packet collisions inherent in asynchronous networks, we developed a specialized MAC-layer collision avoidance mechanism optimized for underwater acoustic communication characteristics, specifically accounting for long propagation delays and effectively mitigating collisions when multiple nodes detect events in close temporal proximity or when multiple forwarding candidates wake up concurrently. The protocol employs a sender-initiated approach that allows nodes to remain silent until events occur, thereby reducing acoustic emissions and making the network less susceptible to detection. We validate the protocol through a comprehensive evaluation comprising hardware implementation, hardware-in-the-loop simulations, and sea trials in the Adriatic Sea. Comparative analysis against a state-of-the-art benchmark demonstrates significantly lower event-reporting delay and reduced per-event energy consumption under equivalent duty-cycle conditions. Experimental results further confirm efficient power management and reliable data delivery even in highly challenging underwater acoustic environments, making the protocol particularly suitable for long-term covert underwater monitoring applications where both performance and stealth are essential.

This paper presents a proposal for a new chaotic-based underwater acoustic modulation scheme. The proposed method is a differential chaotic shift keying modulation based on the Lorenz attractor. Unlike conventional techniques that use Chirp signals, synchronization is achieved using a chaotic signal. In the demodulator, a Doppler shift compensator is also implemented, capable of compensating shifts up to 10 m/s. This compensator is based on bank of Doppler shifts. In order to see the influence of underwater acoustic channel on the proposed acoustic signal, the simulations are performed. The channel was modeled by adding white Gaussian noise with a signal-to-noise ratio (SNR) ranging from -5 dB to 20 dB, multipath propagation with 7 received waves, and the Doppler effect with a speed of ±10 m/s.The experimental verification of the proposed waveform was conducted in an anechoic tank at the SEA Laboratory at the University of Newcastle, as well as during sea trials in Kumbor, Montenegro. The experiments tested the influence of high impulsive noise generated by crustaceans and the presence of high noise generated by vessels. Simulation results and experimental verification demonstrated that the proposed modulation technique is resistant to underwater noise, both Gaussian and impulsive, and is suitable for operation in complex channels with significant multipath fading and attenuation. Furthermore, it offers the advantage of being environmentally friendly.

Underwater acoustic (UWA) network protocol design is a challenging task due to several factors, such as slow propagation of acoustic waves, low frequency bandwidth and high bit error and frame error rates often encountered in real UWA environments. In this paper, we consider the design of a robust and scalable data gathering protocol for UWA sensor networks (UASNs), focusing on practical considerations and lessons learnt from multiple lake and sea trials. A cross-layer protocol is presented that integrates a network discovery process, intelligent routing, scheduling via Transmit Delay Allocation MAC (TDA-MAC) and multi-node Automatic Repeat Request (ARQ), to facilitate reliable data gathering in practical UASN deployments. Furthermore, this paper presents the details of a novel experimental testbed and underwater sensor node prototype that were used for the trials reported in this study. Based on the results of the trials, important conclusions are drawn on the protocol features required to achieve reliable networked communication in realistic UWA environments. The insights gained from the trials are valuable both for further development of the proposed data gathering protocol, and for the wider UWA networking research community concerned with developing practical solutions for real-world UASN deployments.

To enable long-term, large-scale, dense underwater sensor networks or Internet of Underwater Things (IoUT) this research investigates new novel waveforms and experimental prototypes for robust communications on ultra-low-cost and ultra-low-power, miniature acoustic modems. Spread-spectrum M-ary orthogonal signalling (MOS) is used with symbols constructed from subsequences of long pseudorandom codes. This decorrelates multipath signals, even when the time-spread spans many symbols, so they present as random noise. A highly cost-engineered and miniaturised prototype acoustic modem implementation was created, for the 24 kHz–32 kHz band, with low receive power consumption (12.5 mW) and transmit power of 3 km in lakes and >2 km in the sea including severe multipath. In lake testing of a 7-node, multi-hop, sensor network with TDA-MAC protocol, packet delivery was near 100% for all nodes. Trials of acoustic sensor nodes in the North Sea achieved 99.5% data delivery over a 3-month period and a wide range of sea conditions. Modulation and hardware have proven reliable in a variety of underwater environments. Competitive range and throughput with low cost and power are attractive for large-scale and long-term battery-operated networks. This research has delivered a viable and affordable communication technology for future IoUT applications.

This paper presents the development of a low-energy passive acoustic vessel detector to work as part of a wireless underwater monitoring network. The vessel detection method is based on a low-energy implementation of Detection of Envelope Modulation On Noise (DEMON). Vessels produce a broad spectrum modulated noise during propeller cavitation, which the DEMON method aims to extract for the purposes of automated detection. The vessel detector design has different approaches with mixtures of analogue and digital processing, as well as continuous and duty-cycled sampling/processing. The detector re-purposes an existing acoustic modem platform to achieve a low-cost and long-deployment wireless sensor network. This integrated communication platform enables the detector to switch between detection/communication mode seamlessly within software. The vessel detector was deployed at depth for a total of 84 days in the North Sea, providing a large data set, which the results are based on. Open sea field trial results have shown detection of single and multiple vessels with a 94% corroboration rate with local Automatic Identification System (AIS) data. Results showed that additional information about the detected vessel such as the number of propeller blades can be extracted solely based on the detection data. The attention to energy efficiency led to an average power consumption of 11.4 mW, enabling long term deployments of up to 6 months using only four alkaline C cells. Additional battery packs and a modified enclosure could enable a longer deployment duration. As the detector was still deployed during the first UK lockdown, the impact of COVID-19 on North Sea fishing activity was captured. Future work includes deploying this technology en masse to operate as part of a network. This could afford the possibility of adding vessel tracking to the abilities of the vessel detection technology when deployed as a network of sensor nodes.

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.

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 23.4bit/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 100 m 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 0dB for the rates 23.4 bit/s and 375.7bit/s respectively.

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 (MOCK) 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 MOCK 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.