Research On Energy-Efficient Strategies Of Underwater Wireless Sensor Networks

As humans'demands for marine resources increasing, many countries in the world have developed new underwater devices for information acquisition. Underwater wireless sensor networks (UWSN) appears with the excellent information perception, acquisition, processing and transmission, which have largely been applied in many fields, such as underwater targets detection and localization, oceanographic data collection, disaster prevention and resources exploitation. So it opens up a fire-new field in information industry. With the development of UWSN, many kinds of important technologies, for example, the node localization technology, the energy-efficient technology and the network communication technology, are also improved. Not only is the energy-efficient technology the basis of many other technologies, but also as an important reference can demonstrate the performance of other technologies. Therefore, our work will mostly focus on how to save node's energy and balance energy consumption of the networks.This paper firstly reviews the research status of energy-efficient strategies in UWSN, and also introduces the characteristics of underwater acoustic channel. Moreover, two main reasons which affect the network lifetime are analyzed. One is that each sensor node carries very limited energy. The other is that underwater acoustic channel has slower transmission speed, longer transmission delay and higher transmission loss than the radio channel, which restricts acoustic signals. Then, compared with the existing energy-efficient strategies in networks, we get down to discussing them from two aspects.On the one hand, a few researches have shown that a good network topology can reduce communication interference among nodes. Therefore, we can use the topology control to efficiently utilize nodes'energy, and thereby prolong the lifetime of the networks. At first, this paper introduces graph theory in the network topology control, and we can find a few drawbacks of several typical topology control algorithms based on minimum spanning trees. Afterward, with the contradiction between network communication interference and data transmission path explained, the notion that reducing network communication interference is equal to saving network energy consumption is concluded. So we propose a topology control algorithm, the Average Interference Confining topology control algorithm (AIC). The algorithm takes interference strength as the weight of the links between any nodes in networks. So when a node constructs its local topology, it preferentially considers the links'interference strength, thus the whole networks' interference strength will be lowered, and the network lifetime will eventually be prolonged. At the same time, the local topology of each node is built according to angular sectors that are formed by dividing the communication range of the node. Due to each local topology including several minimum spanning trees, the data transmission paths between nodes are increased. Furthermore, the average interference of the local topology confines the links with higher interference strength. In this sense, the algorithm AIC actually creates a good trade-off between reducing network communication interference and increasing data transmission path.On the other hand, compared with traditional networks, the routing protocols of UWSN take energy as the first choice. Moreover, the most important goal of routing protocols design is prolonging network lifetime. That is, a good routing protocol can save nodes' energy and balance energy consumption of networks. Therefore we can design efficient routing protocols to accomplish the goal. Firstly, we introduce main characteristics of the routing protocols of UWSN and the existing routing protocols based on different classification standards. Then, by describing the construction of traditional energy routing protocols, we find these protocols have one-sidedness to deal with the problem about energy consumption of networks. So considering all factors which influence the construction of the routing protocols, we propose an Excellent-Choosing Energy Routing Protocol. The protocol transforms the route selection into the non-linear programming problem. In this protocol, the objective function is established involving nodes' residual energy, communication energy consumption between any nodes and hop numbers. By the solution of the objective function with restricting conditions, the best data transmission path will be found. The protocol achieves balancing energy consumption of networks.At last, we simulate and evaluate these two proposing energy-efficient strategies on ideal underwater acoustic channel. First of all, the network topologies under the algorithm AIC is proved theoretically, and then the algorithm is compared with other algorithms based on minimum spanning trees from network communication interference, average node degree and links'energy consumption. The results of simulation show that the network topologies under the algorithm AIC have lower communication interference, improve network performances, and prolong the network lifetime. Secondly, we use the network simulation software OPNET to design the excellent-choosing energy routing protocol. We process the simulation from the lifetime of the single node and the whole network. Compared with traditional energy routing protocols, the simulation results show our protocol can efficiently save nodes'energy, and prolong network lifetime.