Distributed Medium Access Control Strategies for MIMO Underwater Acoustic Networking

The requirements of multimedia underwater monitoring applications with heterogeneous traffic demands in terms of bandwidth and end-to-end reliability are considered in this article. To address these requirements, a new medium access control protocol named UMIMO-MAC is proposed. UMIMO-MAC is designed to i) adaptively leverage the tradeoff between multiplexing and diversity gain according to channel conditions and application requirements, ii) select suitable transmit power to reduce energy consumption, and iii) efficiently exploit the UW channel, minimizing the impact of the long propagation delay on the channel utilization efficiency. To achieve the objectives above, UMIMO-MAC is based on a two-way handshake protocol. Multiple access by simultaneous and co-located transmissions is achieved by using different pseudo-orthogonal spreading codes. An algorithm is proposed that, in a cross-layer fashion, jointly selects optimal transmit power and transmission mode through the cooperation of transmitter and receiver to achieve the desired level of reliability and data rate according to application needs and channel condition. Extensive simulation results show that UMIMO-MAC increases network throughput, decreases channel access delay, and decrease energy consumption compared with existing MAC protocols for UW-ASNs.