An energy-efficient relay node selection scheme for underwater acoustic sensor networks

Underwater acoustic sensor networks (UWSNs) have many important applications, such as natural resource development, geological oceanography and environmental monitoring. Information collected by sensor nodes must be transmitted to sink node(s) directly or through intermediate nodes. Energy efficiency is a challenging issue for UWSNs because their batteries cannot be removed and are difficult to recharge. Thus, selecting energy-efficient paths from source nodes to sink node(s) is crucial in routing for UWSNs. In this paper, we propose a scheme of relay node selection in UWSNs with a square grid topology for long-term marine monitoring applications. First, we formulate the relay node selection problem as a linear programming problem, where the objective is to maximise the network lifetime. Then, we propose a routing metric that reflects both the transmitting power level and the residual energy of the two-end nodes of each acoustic link. Finally, we evaluate the performance of the proposed relay node selection scheme for different network sizes and different initial battery energy assignments. The simulation results show that the proposed relay node selection scheme can prolong the network lifetime of different network sizes. Compared to a routing algorithm solely based on minimum hop, the performance of the proposed scheme is closer to the optimal value obtained by solving the linear programming problem. Moreover, the network lifetime is further increased if we allow nodes to have different initial energy values based on their work loads.