Robust time-division channel-access approach for an ad hoc underwater network

An ad hoc underwater network is formed by a cluster of stationary nodes that can act as a source, destination, or a relay, in which data packet usually travels across multiple hops. Using a time-division scheme where the propagation delay between the nodes is used as a packet queuing buffer optimises throughput. This requires accurate knowledge of the relative ranges of all the nodes, a high level of accuracy in time-synchronisation, and restricts changes in the position of the nodes especially in the absence of a central server or master node within the network. A method that offers greater robustness is by using a time-slotted approach, where each node is offered a time-slot sufficient for one transmission to reach its maximum effective range. A passive acknowledgement scheme is implemented where a node listens for acknowledgement when the transmitted is being relayed. Nodes monitor other time-slots for the opportunity to contend for idle slots in order to enhance throughput. Results obtained from simulations demonstrate that this method is robust in supporting changes in the relative distances between the nodes, and can operate with a time synchronisation error of up to 1 second.