Research Into Prolonging The Lifetime Of Underwater Acoustic Networks

With the advances of ocean exploitation and ocean military technology all over the world, the field of underwater acoustic (UWA) networks has become a new kingdom of computer science with great foreground. Underwater communication applications mostly involve long-term monitoring of targets, which will find applications in disaster prevention, object localization and tracking, oceanographic data collection and tactical surveillance applications. More and more researchers from academe and military world are engaged in the development of UWA networks due to the great promise and potential in many application areas.The shallow-water acoustic channel differs from radio channel in many aspects. The available bandwidth of the UWA channel is limited and depends on both distance and frequency, and the propagation speed is five orders of magnitude lower than that in radio channel. Besides, the battery-powered nodes limit the lifetime of UWA networks.This paper pays special attention to how to save energy and extend network lifetime. First of all, it introduces wireless sensor networks and UWA networks, including their characteristics, applications and the related research areas. Then the network communication structure and energy consumption model are analyzed. In view of the existing energy-saving strategies, we make the study from the following two aspects:Because data transmission consumes much energy, designing energy-efficient routing protocol enormously faces challenges to make sure the sensors could work as long as possible. Some protocols only consider energy consumption of the entire network and ignore that of the single node, which lead to the failure of the UWA network. The routing selection algorithm we introduced is an effective way to solve the load-balanced problem. The energy balance property guarantees that average per sensor energy dissipation is the same for all sensors in the network, and it prolongs the network's lifetime by avoiding early energy depletion of sensors. For example, in direct transmission, the node farthest away from the base station will first die, and in the multi-hop transmission, the node closest to the base station will first die. According to a hybrid of algorithm-type and the probability of direct transmission, nodes alternately choose the direct transmission and multi-hop transmission to achieve the purpose of energy balance.Nodes in the practical UWA networks are distributed densely and their sensing ranges overlap each other, which produce much redundant data. Therefore, how to conserve energy by decreasing redundancy is an essential problem. Based on the concept of sensing radius, we presents active nodes routing selection (ANRS) algorithm to prolong the lifetime further, which combines the active nodes selection (ANS) algorithm and the optimized RSA algorithm. ANS algorithm increases the number of nodes in the sleep state, and at the same time the entire target is detected during a period of time.Then theoretical analysis and experimental implements of the above algorithms are reported. According to the characteristics of UWA networks, the comparative performance evaluation on the network lifetime and node energy consumption of direct transmission, multi-hop transmission and the RSA algorithm is presented in terms of the effect of distance between the adjacent nodes, frequency and the number of nodes. The simulation results show that the proposed routing algorithm can save and balance node energy greatly, which improves the network performance and prolongs the lifetime of networks. Then, we make the simulation of ANS algorithm, which eliminate redundancy by decreasing the number of actives nodes in provided that the total target is detected during a period of time. In addition, the ANRS algorithm-based strategy of UWA networks improves network lifetime more effectively than the RSA algorithm-based strategy.