Significant advances have been made over the past decade to establish high performance acoustic communication links for many ocean environments. However, there has been limited development on underwater acoustic networks, the fact that is in stark contrast with the terrestrial wireless networks. In an underwater environment, network nodes are neither small nor inexpensive, and the harsh environment renders network deployment difficult. Network design is challenged by the fundamental nature of underwater sound propagation: channel attenuation depends on the distance and signal frequency, resulting in a distance-dependent bandwidth; extensive time-varying multipath causes delay spreads of tens or hundreds of milliseconds, and low speed of sound (1500 m/s) results in severe motion-induced Doppler distortion and extreme channel latency. These facts necessitate dedicated design of communication algorithms and protocols on all network layers, their cross-coupling, as well as careful consideration of the overall system topology and architecture.
In the design of underwater wireless networks, the challenge is to exploit, rather than avoid the peculiar effects of acoustic propagation. Towards this goal, emphasis is placed on three areas: architecture design (determining the degree of hierarchy and multi-hopping, and associated algorithms and protocols), system optimization, and resource allocation (power and bandwidth).
Currently, no analytical results exist on optimized network deployment; furthermore, system capacity is unknown. Anaytical Results that are based on physical laws of acoustic propagation, and not on radio-like models, are expected to provide useful tools in the design of future networks challenged by high latency and limited resources.
