Clustering-based Efficient Routing Protocol For Wireless Sensor Networks

Wireless sensor networks consist of a large number of multi-functional,low-power and inexpensive sensor nodes.Nodes transmit information by self-organized wireless communication and cooperate to accomplish specific tasks.Wireless sensor networks have advantages of flexible deployment,easy extension,low cost,and fast information collection from the surrounding environment.WSNs have been widely applied in many fields such as industry,agriculture,military applications,environmental monitoring,traffic management,and medical and health.Due to resource-limited sensor nodes and restrictions of external environment conditions,extending operating cycle of WSNs is a very important issue.When designing hierarchical routing protocols for WSNs,appropriate distributions of cluster heads can shorten spatial distance to the next hop node so as to effectively reduce energy consumed by data forwarding.Thus operating cycle of the WSNs can be extended.It is feasible to abstract nodes as points distributed over geographic space,and use data clustering techniques such as the K-Means algorithm to generate cluster heads for WSNs.However,the traditional K-Means algorithm need to be iterated several rounds to finally generate accepted distribution of cluster heads,which means that such kind of clustering process has a long delay and increased nodes' energy consumption.Additionally,it is not discussed how to choose the value of K.This dissertation studies efficient routing protocols for wireless sensor networks based on clustering techniques.The work of this dissertation is summarized as follows:1.When designing cluster-based routing protocols for WSNs,carefully selected cluster heads help reduce nodes' energy consumption and extend network life cycle.However,randomized clustering algorithms such as the LEACH protocol(Low Energy Adaptive Clustering.Hierarchy)are difficult to effectively control distance between nodes.Clustering structure yielded by data clustering algorithms ensure that distance between cluster member nodes and the corresponding cluster head nodes are optimized.This dissertation generates cluster heads based on an approximate solution to the K-center clustering problem with approximate ratio 2.Advantage of this solution is that cluster structure close to optimal solution can be generated in one pass without having to be iterated repeatedly.The value of parameter K is generated by an variation to the LEACH threshold formula.Next,the presented scheme forms a chain structure within each cluster,and connects K cluster head nodes via a tree structure to forward packets to the base station.Simulation results show that compared with the existing schemes,the proposed scheme can effectively extend network life cycle.2.Based on the K-center clustering problem,a three-layer WSN clustering protocol is proposed,which can further shorten distance between one node to the next hop.The key point is how to choose the value of the number of primary cluster heads K and the number of secondary cluster heads J.By analyzing and optimizing the overall energy consumption of node when forwarding packets under the three-layer structure,the values of parameters K and J are determined.On this basis,a three-layer cluster structure of WSN was generated based on the K-center clustering problem.Simulation results show that the three-layer structure effectively prolongs life cycle of WSNs.3.Due to interference of external environment conditions and limitation of nodes'resources,it is very important to design a fault-tolerant and reliable WSN cluster routing protocol in condition that nodes may mal-function.Existing WSN fault-tolerant clustering routing protocols require that cluster heads periodically send packets to a base station.The base station can perform global clustering after detecting failed cluster heads.The proposed solution requires cluster members to select the cluster head within one-hop communication range.Then cluster member nodes can monitor status of the adjacent cluster head.When cluster member nodes detect a failed cluster head,they re-select cluster heads within one-hop range and re-join.If necessary,re-generate new cluster heads to complete local re-clustering.Simulation results show that local detection and local re-clustering not only provide fault tolerance to mal-functioned cluster heads,but also effectively extend life cycle of WSNs.