Coverage is one of the important criteria of quality of service in wireless sensor networks. It shows how well an area is monitored by sensors. In many applications, the area should be covered well, and then the network starts working. So, coverage is assumed one of the important research issues in wireless sensor networks. For complete coverage both static and mobile sensors can be used. In the latter case, fewer sensors are needed. The cost of mobile sensor is much more than static one and it is not economic to use all mobile sensor networks. Therefore, in most applications hybrid wireless sensor network is preferred. In These networks great percent of sensors are static and a small number of mobile sensors are used to reach better performance in network. As the energy resource of sensors is limited, it is important to consider mobile sensors movement in network. The other point in wireless sensor network is to reduce the amount of data transmitted in network. When the number of active sensors is more than needed, it causes an increase in the overlap of sensed area and as a result a huge amount of data is produced. To transmit such amount of data along the network, much of sensors resource is wasted. So, methods using minimum active nodes to cover an area are important. Considering what is discussed, in this thesis a new coverage algorithm in hybrid wireless sensor network is proposed. The objective of this algorithm is to maximize the coverage of the region while using minimum number of active sensors. To reduce network constitution cost, the best ratio of the number of mobile to static sensors is found. The other quality of the proposed algorithm is to limit movement of mobile sensors to heal coverage holes. At last, efficiency of proposed algorithm is measured by doing various simulations. Results of simulations show good performance of algorithm in coverage and network cost constitution viewpoint. After reaching complete coverage, it is important to maintain network in this situation for a required time. Since some sensors may die during network lifetime, due to various reasons, performance of network is affected and the quality of coverage decreases. In continuous, an effective algorithm to remove coverage holes is proposed. The average movement of sensors in this algorithm is reduced relative to other existing methods. Keywords: Wireless sensor networks, hybrid wireless sensor networks, coverage, energy, Genetic algorithm.
