Medium Access Control mechanism for Multi-hop Underwater Acoustic Networks utilizing time reversal

In Multi-hop Underwater Acoustic Networks (MUANs), Medium Access Control (MAC) protocol has attracted strong attentions due to its potentially large impact to the overall network performance. The main task of a MAC protocol is to prevent simultaneous transmissions or resolve transmission collisions of data packets while providing energy efficiency, low channel access delays and fairness among the nodes in a network. Unlike terrestrial networks, which mainly rely on radio waves for communications, MUANs utilize acoustic waves, which pose a new research challenge in the design of MAC protocols. In this paper, we propose a new MAC strategy for MUANs utilizing time reversal (TR), to overcome the medium access control problems encountered under the environment of underwater acoustic networks. Utilizing the complex spatial varied features of underwater acoustic channel, time-reversal (TR) process could concentrate signal energy in both the spatial and temporal domains, a useful property for networks in an environment with significant multipath. Utilizing time reversal (TR), the proposed MAC strategy results in a significant improved spatial multiplexing ratio of the shared wireless channel, and resolves collision of simultaneous transmissions in multi-hop underwater acoustic networks.