Underwater communication and ranging systems for software defined acoustic modems

This thesis investigates the design, development, and experimental validation of underwater communication and ranging systems using low-cost software-defined acoustic modems. Underwater acoustic communication remains the only practical solution for medium- and long-range wireless connectivity beneath the surface, yet the acoustic channel is inherently challenging due to limited bandwidth, strong multipath, long propagation delays, and high temporal variability. Novel solutions to these challenges are required by the growing deployment of small, low-cost autonomous underwater vehicles (AUVs) and sensors, which needs communication and localization solutions that are simultaneously reliable, energy-efficient, and affordable. The research begins with the development of ranging and localization methods, exploiting both two-way and one-way travel-time techniques, along with MAC-agnostic protocols that integrate distance estimation into data exchange while minimizing network overhead. Machine learning–based prediction methods are proposed to reduce reliance on precise sound-speed measurements, and statistical channel models derived from field data improve the realism of network simulations. A central contribution of this thesis is the development of a low-cost software-defined acoustic modem, implemented using off-the-shelf hardware and flexible software frameworks. These devices demonstrate robust communication and ranging performance while offering adaptability to support new algorithms and waveforms in real-world deployments. Another key contribution is the design and validation of affordable transducers, a component traditionally cost-prohibitive, thus enabling wider adoption of low-cost platforms for academic, industrial, and community applications. Finally, simulation studies, laboratory experiments, and sea trials validate the proposed architectures and devices, confirming their technological maturity and suitability for scalable, cost-effective underwater networks. This thesis contributes to democratizing underwater acoustic communication research and lays the groundwork for cooperative swarms of underwater vehicles and distributed marine sensing systems.