The Research On Topology Control For Wireless Sensor Networks

The wireless sensor networks is a distributed sensing detection system, which is constituted by many wide spread nodes in a region. In this system sensor nodes gather and deal with data in the region. Then results data is transmitted to a sink node through multi-hop and finally to the console. So it implemented the data collection and the monitoring mission. Compared with traditional wireless networks, this wireless sensor network with low cost node, no infrastructure, well adapted to high dynamic topology, and other good characteristics, have received increasing attention.As a foundation of networking and communication in wireless sensor networks, topology control has a direct impact on wireless sensor networks in all its aspects. By controlling the active state of nodes or links, topology control not only can reduce network energy consumption, extend the network lifetime, but also can reduce communication conflicts occurred in the data link layer and reduce the complexity of network routing. In this paper, the formation of the physical topology and controlling of the logical topology in wireless sensor networks are studied based on the characteristics of wireless sensor networks. Main research are presented in the followings.The formation of physical topology in wireless sensor network which is also known as node deployment, is the problem that must be faced up firstly in the study of wireless sensor networks. Fixed deployment can be deployed and adjusted on the application required, and can substantially reduce costs and better adapt to the application. Based on the analysis of the distribution of energy consumption in wireless sensor networks, two distribution density function of nodes deployment achieved according to relationship between the radius of node sensing and radius of node communication: node distribution density function with coverage priority and node distribution density function with connectivity priority. According to these distribution density functions, more nodes should be deployed at the location near the sink nodes to make the total energy of each location in entire network and its total load to maintain a certain proportion. The node deployment can guarantee effectively the coverage and connectivity, under the premise of extending the network lifetime. Because of the broad deployment region and weak ability in communications of wireless sensor networks, it is often clustered. This article discusses two types of clustered network topology: homogeny cluster head hierarchical topology and heterogeneous cluster head hierarchical topology. In heterogeneous cluster head hierarchical topology, appropriate communication modes, single-hop or multi-hop, should be selected first according to the communications environment within the cluster. Then the number of cluster head and the communication radius of ordinary nodes within the cluster are calculated according to different modes of communication. With these two parameters, each sensor node can add to the cluster nearest to complete the process of clustering. In homogeny cluster head hierarchical topology, the article first discusses the selection of cluster head. With a given formula on weights, a suitable cluster head node is selected. And according to the relationship of location with cluster head node, the gateway nodes and the distributed gateway nodes are selected. Because of intensive deployment, node failure often occurred in wireless sensor networks. In order to overcome the effects of node failure, it should add a certain degree of redundancy to topology obtained in the previous to construct a fault tolerance topology.At the time driven wireless sensor network, sensor node collect data and report it to sink node at a fixed time interval. When there is no data to report, node can enter sleeping to save energy consumption. This paper presents a intra-cluster sleeping scheduling mechanism, which does not require strict time synchronization mechanism. Each sensor node synchronizes its time by the information exchange between the cluster head node and itself. The mechanism has also taken a different sleeping scheduling mechanism for the different types of nodes determined by clustering algorithm.A mobile sink node can avoid the excessive energy consumption of node which is close to sink node. In this paper, sink node move tightly in each location to make sure that each moving of sink node has not very big impact on the entire network topology and can balance energy load with an accumulated, thus prolonging the network lifetime. In the process of the research, we should only take the backbone of network into account. When the main traffic flow from direct neighbor node changes, we consider that the abnormal load may occur and sink node need to be moved. The direction of movement is to where sink node can alleviate excessive energy consumption and traffic flow. Direction of movement can be achieved by calculating the weighted centroid of the neighbor node with mainly traffic of those vulnerable nodes. The weight is achieved by the normalized mainly traffic flow divided by normalized energy of the node. The moving distance should be limited with the largest change rate of sink node coverage or the mathematical expectation of moving distance.