| dc.description.abstract | Wireless Sensor Network (WSN) is an emerging research filed and its technology can be widely utilized in many applications especially in environmental surveillance. However, there are exist some holes within the WSNs caused by some factors such as non-uniform deployment of sensor nodes or the existence of physical obstacle such as mountains and lakes or some sensor nodes deplete their energy or be destroyed by outside forces. These holes will degrade the performance of several routing protocols. Hence, how to discover the boundary nodes surrounding the holes and then utilize the information of boundary nodes for routing protocols to avoid holes in advance and to improve the performance of various applications is a significant research issue. In order to solve this problem, firstly, we propose the Boundary Node Selection and Target Detection protocol where each node has location information. This protocol, in short time, prior to discover some extreme nodes having extreme value of coordinates as the initial boundary nodes surrounding the holes and monitoring region in distributed manner. Then the protocol finds out other remaining boundary nodes based on these extreme nodes. The simulation results show that this protocol can cost few control packets overhead to find out boundary nodes soon and the number of selected boundary nodes comparing the optimal value is approximate. However, in some situations, the sensor nodes cannot obtain location information. Therefore, we propose the Hole Detection and Boundary Recognition protocol. This protocol can discover the boundary nodes by only utilizing the connectivity information among nodes when nodes have no location information. The protocol creates the Virtual Hexagonal Landmarks and then selects the landmarks surrounding the holes and sensing field. Based on this selected landmarks, the protocol further finds out correct boundary nodes. The simulation results show that the protocol has better performance of the accuracy ratio of selecting correct boundary nodes even in low node degrees. Eventually, the information of these boundary nodes should be transmitted to the Sink or some specific data centric nodes and the data packets can avoid the holes when transmitting. Therefore, we propose Routing with Hexagonal Virtual Coordinations protocol. Based on the Virtual Hexagonal Landmarks of previous protocol, the virtual coordination is created. Before transmitting data packets, the protocol uses this virtual coordination to create an Auxiliary Routing Path to indicate the direction of the journey from the source to the destination. When transmitting the data packets, the routing paths assisted by the Auxiliary Routing Path are not always fixed even from same source to destination. The simulation results show that the protocol can find a load balancing routing path to the destination and then prolong the network lifetime.
| en_US |