Impact of reverberation levels on short-range acoustic communication in an underwater swarm sensor network (USSN) and application to transmitter power control

The progress of Underwater Swarm Sensor Networks (USSNs) has required the development of new approaches and understanding to short-range mobile acoustic underwater communication. This communication is essential in USSN to coordinate the manoeuvring of the closely operating vehicles as well as to transmit data within the swarm to gain benefits of operating as a team. Implementation of swarms of vehicles will greatly improve on the current ability of single vehicles to survey and explore the oceans. We propose that with the application of an underwater swarming network, which has many vehicles in a dense topology, there will be an impact on the reverberation channel geometry due to the vehicles themselves being `sound reflective' objects and therefore on the overall reverberation levels that will be experienced in these networks. Thus a new type of reverberation, swarm scattering will be discussed. It is shown here that the relationship between range (propagation time) and packet length (transmission time) plays an important role in swarm scattering reverberation levels for an USSN. In addition this paper also investigates the impact that reverberation levels (in particular swarm and sea-surface scattering) will have on the SNIR (Signal to Noise + Interference Ratio) and the influence that transmitter power will have on this ratio for autonomous vehicles operating at short-range in a swarm like fashion. It is shown that knowing the relationship between transmitter power, reverberation levels and SNIR can be beneficial in a vehicle for predicting optimal transmitter power levels in a similar way to the feedback obtained in terrestrial networks. Optimising the energy levels used to send packets will be beneficial for both reducing energy consumption as well as increasing success of packets being delivered without error. OpNet Modeler has been used to model the operations of a MAC protocol specifically designed for an USSN and to analyse the impact of these reverberation levels on SNIR.