An Energy-Conserving Collision-Free MAC Protocol for Underwater Sensor Networks

An underwater sensor network (UWSN) has recently attracted considerable attention due to its ability to discover and monitor the aquatic environment. However, its acoustic communication has posed several inherent characteristics, such as high latency, low available bandwidth, and high bit error rate. These unique characteristics have made contention-based medium access control (MAC) protocols inefficient for UWSNs. They are most expensive and are not as effective as they are in terrestrial networks. Through this principle, a contention-free MAC protocol is, therefore, considered to be more reliable and flexible to overcome the consequences of applying acoustic signals and also to achieve a high performance (improving the energy efficiency and throughput across the network) by eliminating the chance of collision. In this paper, we propose a novel energy-conserving and collision-free depth-based layering MAC (DL-MAC) protocol for UWSNs. DL-MAC is able to deal with the underwater MAC challenges, such as the near-far effect, spatial-temporal uncertainty, and hidden/exposed terminal problems. It is able to efficiently schedule the transmission and reception operations in each side by using the concept of layering and a distributed clustering algorithm. By using a TDMA-based principle, DL-MAC can assign separate time slots to every sensor node individually to access the medium without any possibility of collision. Our extensive simulation study shows that DL-MAC outperforms other protocols in terms of throughput, packet delivery ratio, energy consumption, and packets lost under varying traffic rates and the numbers of nodes.