Quality of service and security in multimodal networks of underwater drones

The central element of Internet of Underwater Things (IoUT) is embodied by Underwater Wireless Sensor Networks (UWSNs): these networks are composed of nodes usually equipped with sensors functional to the particular phenomenon to monitor in the specific area of interest. Such nodes often consist of low-power computational boards that are battery-powered and capable of wireless communication; they are then water-proofed and moored to a buoy and optionally anchored to the seabed, thus obtaining a static node. More recently, and depending on the reason of deployment, UWSNs have been encompassing a mixture of static and mobile nodes, the latter ones represented by underwater robots (or drones) that may either be remotely piloted or operate autonomously. This thesis presents techniques aiding the development of end-to-end solutions within the IoUT field, enabling a comprehensive approach to complex underwater systems. In particular, three main directions are identified and tackled, namely: (i.) the enhancement of communication reliability despite channel instability, (ii.) the achievement of trustworthiness and interoperability up to large networks, and (iii.) the improvement of simulation tools towards greater realism during early-stage design phases. Along the first direction, a Medium Access Control (MAC) protocol that explicitly takes into account the time-varying nature of the underwater acoustic communication channel is presented. This MAC protocol jointly optimizes packet transmission scheduling and error-correction coding, observing Signal-to-Noise Ratio (SNR) figures and queued packets, by exploiting an underlying Reinforcement Learning agent. Moreover, this protocol is widely applicable in many scenarios, given its tunable behavior in favoring higher reliability (for fault-critical networks) or lower latencies (for time-sensitive networks). Following with the second direction, a lightweight and low-bandwidth Authentication and Identification protocol for UWSNs is introduced. This protocol is specifically designed to support interoperability among UWSN nodes owned by multiple organizations, leveraging Distributed Ledger Technology and Decentralised Identities to guarantee message confidentiality, authentication, and integrity through a standard cryptographic suite. Concluding with the third direction, a simulator targeting complex UWSNs settings, i.e. static nodes plus multiple underwater robots, is detailed. This simulator builds on top of open-source software that is widely used by respective networking and robotics research communities, namely ns-3 and Gazebo/UUV Simulator, and provides a bridging and synchronization protocol among them. Moreover, UUV Simulator is extended to enable deeper environment and sensor configurations, out-of-the-box ranging and mission applications, as well as localization algorithms. The extensions to ns-3 introduce multimodal communication capabilities (acoustic, wireless optical, electromagnetic) support for multiple self-configuring networking protocol stacks, and a set of widely used network performance metrics.