Sea trials of an underwater, ad hoc, acoustic network with stationary assets

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 arriving 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 time-division 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.