A multi-channel MAC protocol for underwater acoustic networks

In underwater acoustic networks (UANs), the “hidden terminal” and “exposed terminal” problems greatly restrict their capacity due to the characteristics of the underwater acoustic channel, such as very limited bandwidth, time-varying multipath propagation, and large propagation delay. However, it is still possible to achieve reasonably good performance if we smartly leverage large propagation delay. In this paper, we propose a multi-channel MAC protocol for UANs (called UA-MCMA). UA-MCMA divides the available channel into a control channel and several traffic channels, each of which will be uniquely used by one node within its single-hop scope. Unlike conventional handshaking-based schemes that tend to suffer from low throughput and high transmission delay in UANs due to the long propagation delay, the UA-MCMA combats this problem by allowing a sender to start transmitting data packets on its traffic channel periodically after it has sent a request-to-send frame on the control channel, without waiting for the clear-to-send frame from the receiver. By doing so, some data can be transmitted during the channel reservation period, which notably improves the performance of UANs. Simulation results confirm its good performance in terms of throughput and average packet delay.