Underwater acoustic networks (UANs) are an emerging technology for a number of oceanic applications, ranging from oceanographic data collection to surveillance applications. However, their reliable usage in the field is still an open research problem, due to the challenges posed by the oceanic environment. The UAN project, a European-Union-funded initiative, moved along these lines, and it was one of the first cases of successful deployment of a mobile underwater sensor network integrated within a wide-area network, which included above water and underwater sensors. This contribution, together with a description of the underwater network, aims at evaluating the communication performance, and correlating the variation of the acoustic channel to the behavior of the entire network stack. Results are given based on the data collected during the UAN11 (May 2011, Trondheim Fjord area, Norway) sea trial. During the experimental activities, the network was in operation for five continuous days and was composed of up to four Fixed NOdes (FNOs), two autonomous underwater vehicles (AUVs), and one mobile node mounted on the supporting research vessel. Results from the experimentation at sea are reported in terms of channel impulse response (CIR) and signal-to-interference-plus-noise ratio (SINR) as measured by the acoustic modems during the sea tests. The performance of the upper network levels is measured in terms of round trip time (RTT) and probability of packet loss (PL). The analysis shows how the communication performance was dominated by variations in signal-to-noise ratio, and how this impacted the behavior of the whole network. Qualitative explanation of communication performance variations can be accounted, at least in the UAN11 experiment, by standard computation of the CIR and transmission loss estimate.

The NNN-UTS project (Nordområdenes Nye Nervesystem - Undervanns Trådløst Sensornettverk) has aimed to develop wireless network technology for underwater sensor networks, employing acoustic communication to realize wireless functionality in water. Research and development has been carried out in 2006-2009. A final sea test/demonstration of the system was carried out at Breiangen in the Oslo fjord, on December 3-4 2009. The result is a fully operative network system available for water depths down to 4000m.

This paper introduces the underwater acoustic modem as implemented within the UAN - Underwater Acoustic Network project. The low power modem has implemented turbo equalization algorithms in addition to variable spread rate direct sequence spread spectrum signaling. The network layer implemented on the modem support automatic network discovery, multi hop routing and support for mobile nodes, and when expanded with a single board computer via serial line it supports IP connectivity end-to-end. Experimental results from sea trials are presented.

The electromagnetic spectrum’s scarcity, the tactical edge’s dynamic nature, and the variety of tactical operations impose challenges to military cognitive radio networks. Multi-radio dynamic spectrum management (DSM) and routing promise to increase the spectral efficiency and robustness of tactical ad hoc networks by adding key control plane tools that adapt the network to the varying harsh tactical environments. This paper describes a novel concept where implicit spectrum sensing, a distributed DSM architecture with ontology-based spectrum access policies, modified routing and network time synchronization capabilities interplay to address those challenges. The simulation results verify the designed functionality in harsh electromagnetic environments in a multitude of scenario sizes, in terms of number of radio terminals and number of networks. In particular, the simulation of a large operational scenario shows solid scaling capabilities and that ongoing jamming in several networks are efficiently mitigated and low-loss performance are re-established.

An underwater acoustic network (UAN) represents a communication infrastructure that can offer the necessary flexibility for continuous monitoring and surveillance of critical infrastructures located by the sea. Given the current limitation of acoustic-based communication methods, a robust implementation of UANs is still an open research field. The FP7 UAN project moved along these lines, and it was one of the first cases of successful deployment of a mobile underwater sensor network integrated within a wide-area network, which included above water and underwater sensors. This contribution gives details on the UAN network structure and equipment. It reports statistics on the performance of the system as collected during the project final sea trial, which was held in Trondheim, Norway, in May 2011. The UAN network was in operation for five continuous days and was composed of up to four fixed nodes, two autonomous underwater vehicles and one mobile node mounted on the supporting research vessel. Results from the experimentation at sea are reported in terms of channel impulse response and signal to noise plus interference ratio as measured by the acoustic modems during the sea tests. The performance of the upper network levels are measured in terms of round trip time and probability of packet loss. Finally, the experimental results have been compared with those obtained in simulation using the BELLHOP acoustic code, fed with the environmental data gathered during the sea trial.