Adaptive Multimode Medium Access Control for Underwater Acoustic Networks

Standards such as 802.11 have played a key role in the success of terrestrial radio wireless communications. Similar standardization will be needed in underwater acoustic networks (UANs) of the future. One of the important aspects of standardization is UAN medium access control (MAC). Since no single protocol can satisfy the diverse requirements of a general UAN MAC, we explore the possibility of combining multiple MAC protocols into a suite. We also consider physical-layer adaptation techniques as they are closely related to the MAC adaptation. The suite's key protocol mode called MACA-EA is a novel, enhanced adaptation of multiple access with collision avoidance (MACA) as used in 802.11. The suite uses two other modes-a centrally polled mode called MACA-C and a simple DATA-ACK protocol. Using both simulations and mathematical analysis, we compare saturated throughput performance and waiting time performance (in case of Poisson arrivals) of the different MAC protocol modes. We also benchmark the performance against ideal time-division multiple access (TDMA) performance. We present suitable adaptation techniques to switch between the protocol modes based on network requirements, traffic intensity, and quality-of-service QoS) requirements such as maximum allowed waiting time for reliable transfer. We propose an adaptation algorithm for automatically varying the batch size in MACA-C and MACA-EA for optimum performance. A key observation is that for ad hoc UANs, the adaptation of the multiple modes can lead to near-optimal performance across a wider range of traffic intensity, as compared to what any single protocol can achieve.