Energy-Efficient Distributed MAC Protocols for Underwater Sensor Networks
In this thesis, we propose three contention-free MAC protocols which can achieve a better performance by avoiding any possibility of collisions in order to improve the energy efficiency, throughput, and fairness for all nodes in an UWSN. The proposed MAC protocols are summarised as follows: 1. ED-MAC is a new reservation-based MAC protocol which employs a duty cycle mechanism by assigning time slots to every individual node in the network in a distributed manner. This is achieved by using a depth-based timer at each node to prioritise slot reservation depending on the node depth; the greater the depth, the higher priority to reserve a slot. It also addresses the spatial-temporal uncertainty and the hidden node problem. After scheduling the medium access, each node is occasionally awake to either transmit or receive data and sleep when there is no packet to transmit or receive, to conserve energy. 2. DL-MAC is a novel energy-conserving and reservation-based MAC protocol for UWSNs. It addresses the near-far effect, spatial-temporal uncertainty, and hidden/exposed node problems. The depth information of each node is used to divide the network area into a number of horizontal layers, which is classified into three layer-type, and to assign separate frame to each layer-type. Every layer-type is also divided into some clustering groups by using a distributed clustering approach. Every cluster is assigned a sub-frame. All members of a cluster are also assigned a unique slot from the associated sub-frame. 3. Inspired by graph colouring technique, GC-MAC is another reservation-based MAC protocol proposed for UWSNs. It uses a distributed clustering approach for up to two-hop neighbouring sensors after dividing the underwater network area into a number of adjacent cubes, to set a reference point at the centre of each. In this way, GC-MAC is then able to address the near-far effect, spatial-temporal uncertainty, and hidden/exposed node problems. The performance of all proposed MAC protocols are extensively studied through simulation using a widely-used software tool called Aqua-Sim, which is an NS-2 based simulator for UWSNs. Our results show that the proposed MAC protocols outperform other well-known contention-based MAC protocols reported in the literature and achieve a significant improvement under different operational conditions. Finally, a comparison study among our proposed protocols is then conducted under various operational conditions and different assumptions.