Sea trials of an underwater, ad hoc, acoustic network with stationary assets
IET radar, sonar & navigation
The diverse roles of deployable underwater assets have increased the need for ad hoc networking capability. This capability is defined as the ability to form acoustic communication links by deploying assets in a non-deterministic manner, without depending on a priori route and positioning information. Each asset represents a node in the network, and can act as a data source, sink or router, and initiates, stores or relays data, respectively. Data packets may be hopped over a few nodes before
... iving at the designated destination. This ad hoc network consists of two main layers: the medium access control (MAC) layer to resolve node contention, and the ad hoc routing layer to manage routing information. In the MAC layer, both random access and timedivision protocols are applied. The protocol in the routing layer is responsible for route setup and route maintenance. This concept of multiple-hop, ad hoc networking was implemented during sea trials conducted in Portland Harbour, UK, involving up to six nodes. The trial was designed with the aim of gaining application experience in ad hoc network deployment and in assessing the performance of the protocols in a real operating environment. The emphasis was on modem integration, and the stability and reliability of packet transport. The trial results and their subsequent analysis demonstrated the robustness of the network in performing ad hoc routing and resolving node contention in a realistic and acoustically challenging environment. total of 5-15 nodes, sparsely arranged to maximise coverage. Two main target applications for this network are remote environmental monitoring in coastal waters and to provide long-ranges acoustic communication capabilities to AUVs. Owing to the much lower relative throughput of this network, the type of data that can be carried are constrained to low volume traffic such as long-periodic updates of sensor values, or command and control packets to AUVs. Streaming or time-critical data would not be suitable for this network at this stage. A comprehensive and up-to-date survey of the practical issues in underwater networks is presented in [2, 3] . The main contributions of the paper are the application experience and the results obtained from an underwater networking sea trial conducted in a realistic shallow water environment, separated into two parts. The first part demonstrated the implementation of a simple time-division scheme that was enabled by an ad hoc time-synchronisation protocol introduced herein. The second part demonstrated the successful delivery of data packets across a multiple-hop network operating with a random-access scheme, where there were no a priori route information, and where nodes were replaced and relocated after route information were established. A table at the end of Section 2 (Table 1) gives an overview comparison between this work and other known underwater networking research.