An Adaptive MAC Protocol for Underwater Acoustic Sensor Networks With Dynamic-High Load

The channel reservation mechanism is devised to reduce end-to-end delay and improve throughput for underwater acoustic sensor networks (UASNs) with dynamic load. Unfortunately, in dynamic-high-load UASNs, frequent channel reservation will lead to an increase in end-to-end delay and a decrease in throughput due to long propagation delay and collisions. To reduce end-to-end delay and improve throughput, we proposed an adaptive media access control (MAC) protocol for UASNs with dynamic-high load (DHL-MAC). DHL-MAC performs channel reservation before the data packets are actually generated and avoids collisions to reduce the impact of channel reservation on end-to-end delay and throughput. First, the adaptively allocated time slot for the next time frame is obtained based on the estimation factor and secondary transmission data packets, which could reduce idle waiting time. Then, by merging the channel reservation information (CRI) for next time frame into the current data frame, channel reservation is performed before data packet generation to reduce waiting delay. Finally, a dynamic time slot schedule scheme (DTSSS) is proposed to reduce time frame length and achieve collision avoidance. The performance analysis and simulation results show that our proposed DHL-MAC could efficiently reduce end-to-end delay and improve throughput in dynamic-high-load UASNs. Simulation results show that DHL-MAC can achieve a maximum 95.2% reduction in average end-to-end delay and a maximum 56.2% improvement in throughput upper bound compared with reservation-based MAC protocol (R-MAC).