Abstract — The mobility of underwater sensor nodes makes the network topology inconveniently controlled and slowly changed. Thus, in order to enable underwater sensor networks to work more effectively, it is necessary for us to periodically detect the coverage rate and redeploy nodes to non-coverage areas. In this paper, we take the lead in introducing the redeployment issue in underwater sensor networks. In our opinion, the key point of the redeployment issue is coverage. For this special coverage topic, we first propose a coverage rate definition scheme. Then along with the definitions, two redeployment algorithms are introduced, of which one is based on adding new nodes while the other one is by the means of moving redundant ones. By modeling the mobility behavior of underwater nodes with three-dimensional random walks, we employ simulation experiments to verify our ideas, the results of which show the importance of redeployment in the underwater environment. I. INTRODUCTION Although some special applications call for a limit amount of mobile nodes, most sensor nodes in ground-based sensor networks are typically static. In contrast, the majority of underwater sensor nodes, except some fixed nodes equipped on surface-level buoys, are moving continuously due to water current, water temperature and other underwater activities [1]. Therefore, the topology of underwater sensor networks (UWSNs) is inconveniently controlled and slowly changed because of the node mobility. And it is necessary for us to periodically detect the coverage rate and redeploy nodes to non-coverage area to enable UWSNs to work more effectively. Actually, sensor nodes are often spread in a random manner no matter in terrestrial or underwater sensor networks, which may lead to the unfair coverage of event detection for some key areas [7]. And this unfair will be more serious in underwater world due to the nodes’ slowly moving. Some nodes may even move out of a key area, which badly deteriorates the coverage rate. In this paper, we consider a general UWSNs redeployment issue. Aiming at this issue, we first propose a dividing cube method to calculate the coverage rate of an area. Then according to the obtained coverage rate, two redeployment algorithms can be implemented to improve the coverage rate if the coverage rate becomes rather low due to the mobility of sensor nodes. Algorithm I is based on adding new nodes to the largest blind positions while Algorithm II is by the means of moving some redundant nodes from the over-covered positions to other necessary ones. Furthermore, although our algorithms are designed for redeployment, Algorithm I can also be used to guide the initial deployment of sensor nodes, which is still valuable for the stationary environment. The remainder of this paper is organized as follows: In Section II, related works are summarized in brief. Then some definitions of conceptions and redeployment algorithms are proposed in Section III. Section IV gives simulation experiments and evaluation results. Finally, we make some concluding remarks and discuss some future work in Section V. II. RELATED WORKS As the key point of UWSNs redeployment, coverage issue has been widely discussed both in terrestrial and underwater sensor networks. Turn first to the literatures in terrestrial sensor networks. With the assumption that each sensor node has equal distance to its neighbor nodes, Slijepcevic et al. present a heuristic coverage scheme [2]. In [3], a virtual force algorithms (VFA) is proposed to enhance coverage after an initial random placement of sensors in two-dimensional environment. In [4], each node is able to dynamically decide a schedule for itself to guarantee a certain degree of coverage to accomplish differentiated surveillance service for different target areas with low energy consumption. [5] considers coverage and connectivity problem at the same time. It provides a geometric analysis of the fundamental relationship between coverage and connectivity based on a simple circular communication/sensing model at first. Then, a Coverage Configuration Protocol (CCP) that can dynamically configure the network to provide different degrees of coverage as requested by applications is presented. The Redeployment Issue in Underwater Sensor Networks Liu Bin 1 , Ren Fengyuan 1 , Lin Chuang 1 , Yang Yaqin 2 , Zeng Rongfei 1 , Wen Hao 1 1 Tsinghua National Laboratory for Information Science and Technology Department of Computer Science and Technology, Beijing, China {liubin, renfy, clin, zengrf, wenhao}@csnet1.cs.tsinghua.ed.cn 2 Beijing University of Posts and Telecommunications School of Computer Science and Technology, Beijing, China yaqin@bupt.cn This full text paper was peer reviewed at the direction of IEEE Communications Society subject matter experts for publication in the IEEE "GLOBECOM" 2008 proceedings. 978-1-4244-2324-8/08/$25.00 © 2008 IEEE.