Nodes in underwater wireless sensor networks (UWSNs) keep moving and dispersing due to force of water flow and aquatic creatures touching, and thus some isolated unknown nodes emerge. This type of isolated unknown nodes cannot directly communicate with enough beacons in their neighborhoods, which makes localizations for them disabled or the localization error unbearable. To this end, a multihops fitting localization approach is proposed in this paper. Firstly, some intermediate nodes between beacons and unknown nodes are set as routers to construct paths via a greedy method; then, the multihop paths are approximately fitted into straight lines; finally, the positions of unknown nodes can be estimated by trilateration. The proposed algorithm is analyzed and simulated in terms of localization error and error variance, and the results are proven preferable.

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Abstract-Underwater wireless sensor network (UWSN) is a special kind of wireless sensor networkwhich is composed of a large quantity number of wireless sensor nodes deployed in the water. While there are extensive studies on deploy-issue of terrestrial wireless sensor networks (WSN), UWSN has not been paid enough attention due to the challenges of UWSN, such as low available bandwidth, highly varying multipath, and large propagation delays. In this paper, we propose a depth-adjustment scheme to maximize the coverage in 3D space. After deploying nodes in the water surface, we use Voronoi diagram to compute redundant nodes whose disappearance will not decrease the coverage in 2D space, and then we determine the depth that redundant nodes should be moved towards. After all the redundant nodes have moved to the lower layer, the algorithm continues to schedule redundant nodes of the lower layer until 3D space coverage is fulfilled.

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