Research On The Discovery And Restoration Of Blind Spots In Wireless Sensor Networks

Wireless sensor networks (WSNs) consist of low-cost, low-power tiny sensor nodes that can communicate with each other to perform sensing and data processing cooperatively. Coverage control is the key problem of research and application of WSNs. In recent years, the development of MEMS has made the mobile sensors possible. In this thesis, the coverage problem for hybrid networks which comprise both static and mobile sensors is investigated.Since the random initial deployment cannot fully cover the monitoring region, or node failure, energy depletion, and other reasons for the failure of nodes result in coverage blind spots in a network, a discovery strategy of coverage blind spots based on Voronoi diagram is presented in this thesis to solve these issues. Considering the sensor nodes in the monitoring region as the point set in a space, the location information of all the working nodes in the region is collected and the Voronoi diagram is computed to judge whether coverage blind spots exist in the region based on the location information. In order to avoid the redundant coverage when repairing blind spots, the situation that several blind spots exist in the same Voronoi region is considered and a method is proposed to establish a blind spots vertex list in the nodes. By identifying the location of coverage blind spots in the Voronoi region, the forwarding of redundancy information caused by repairing blind spots is reduced.A dynamic repair mechanism based on the ant colony algorithm is proposed for coverage blind spots found in the lifetime of WSNs. With the blind spots and the mobile sensor nodes treated as food and ants respectively, mobile nodes mimic the ants foraging mode to repair the network coverage blind spots. Food odor is diffused in a flooding way and their forward hops are set according to the energy and mobile capacity of the mobile nodes. With the increase of the hops, the odor intensity is reduced. And a random avoidance strategy is designed according to the random waiting time. The repair opportunity is left to the node with sufficient energy and short mobile distance to the blind spot, which makes the repair mechanism more efficiently.Finally, extensive simulations are done to analyze the utilization of the mobile node and node average move distance. Compared with the scheme of using of all static nodes, our method not only can make the nodes deployment more evenly, but also improve the network quality of service, which verifies the effectiveness and feasibility of the restoration mechanism based on ant colony algorithm.