Self-organized And Reconfigurable Clustering Algorithms For Wireless Sensor Networks

In recent years,advances in Wireless Sensor Networks(WSNs)have attracted world-wide attention.Compared with conventional network architectures,WSN technologies have a number of advantages and thus are used in a vast range of application domains.However,there are two severe challenges in WSNs including resource constraints and dynamic environment conditions.Resource constraints of sensor nodes are comprised of limited energy supplies,limited memory,and limited computational capacities.The limited energy supplies of sensor nodes impose constraints on the network lifetime,which necessitates the effective utilization of energy resources.On the other hand,as the network topology may change due to node failure,node mobility,and large-scale deployments,the sensor nodes should possess self-organization capability,which can manage and control themselves efficiently.In addition,sensor nodes may join or leave the current network,which necessitates WSN reconfigurability,in order not to affect the overall goal of the system.To address the above two challenges,the primary method is to implement energy-efficient and adaptive routing protocols on network layer.The network routing protocols include flat routing protocols and hierarchical(clustering)routing algorithms.Compared to the flat routing protocols,the clustering routing algorithms can prolong the network lifetime,improve the network scalability and stability,and many of these algorithms have the characteristics of self-organization and reconfigurability.Therefore,self-organized and reconfigurable clustering algorithms have important significance and research value.To address the issue of unbalanced energy dissipation in homogeneous WSNs,the multi-hop transmission and the technique of multi-objective optimization based on the analytic hierarchy process(AHP)are investigated in this dissertation.For the energy dissipation that the network topology changes incur in heterogeneous WSNs,our solution is to combine static energy heterogeneity with dynamic energy heterogeneity.To solve the problem of energy dissipation and data loss in mobile WSNs,the cluster optimization of mobile WSNs in diverse scenarios is studied in this thesis.For the energy dissipation that occurs in agricultural WSNs,our idea is to combine agricultural WSNs with clustering algorithms.In summary,there are four aspects in this research work:(1)The multi-hop clustering algorithms based on the aggregator and AHP are proposed.A timer that is dependent of the node residual energy is used to compete for the optimal number of cluster heads in the multi-hop energy balancing algorithm based on the aggregator(MEB).Furthermore,data transmission is integrated with intra-cluster routing and inter-cluster routing.On the other hand,the optimized cluster head is selected based on the hierarchical AHP model of multiple factors in the multi-objective distributed clustering algorithm using the AHP(LEACH-AHP).The weight vector of normalized factors is obtained by solving the eigenvector associated with the largest eigenvalue of the constructed compatible AHP matrix.Data transmission is based on the multi-hop transmission among cluster heads and a super cluster head.Simulation results show that MEB is superior to LEACH and TB-LEACH in terms of the node energy balancing and the network lifetime.On the other hand,LEACH-AHP outperforms LEACH,CHEF,and EERC in terms of the cluster structure,the node remaining energy,and the network lifetime.(2)The adaptive clustering algorithm for dynamic heterogeneous WSNs(ACDHs)is investigated.First,the network model for dynamic heterogeneous WSNs is built,and a mathematical estimation and analysis of this dynamic model is given in terms of the network lifetime and data packets of the network.In addition,the number of clusters is optimized for dynamic heterogeneous WSNs.Then,based on this dynamic model,an adaptive clustering algorithm(ACDHs)for adapting to the changes of topology is proposed.In this algorithm,the cluster head is selected according to the node initial energy,the node residual energy,and the network average energy.Finally,the operation mechanism of ACDHs is provided.Simulation results show that the heterogeneity parameters and the dynamic parameter can affect the network lifetime and data packets of the network.Compared with LEACH,SEP,DEEC,TSEP,and ZSEP,the optimal number of dynamic clusters can be obtained in ACDHs.Furthermore,by adjusting the heterogeneity parameters and the dynamic parameter,ACDHs outperforms its comparatives in terms of the network lifetime and data packets of the network.(3)The centralized energy-efficient clustering routing protocol for mobile nodes(CEECR)is developed.In the cluster set-up phase of each round,a centralized cluster formation algorithm is presented to produce an optimal set of cluster heads.Firstly,a set of cluster head candidates is constructed based on node mobility and the node energy property.Based on this set,a simulated annealing optimization algorithm is used to find an optimized set of cluster heads through repeated iteration.In the steady-state phase of each round,as the detached node moves out of its cluster,the combined weights of all cluster heads are calculated by the base station,and then the detached node attaches itself to its optimal cluster head and joins the new cluster.Simulation results show that CEECR outperforms LEACH,LEACH-C,LEACH-Mobile,CBR,MBC,and LEACH-MF in terms of average energy dissipation and packet delivery ratio in three different scenarios.Furthermore,CEECR expends less energy than the distributed protocols in cluster formation,and its performance of reconfiguring clusters is better than that of LEACH.(4)The energy-efficient greenhouse clustering algorithm is investigated.Firstly,the experimental system of WSN in an agricultural greenhouse is introduced,which includes a low power hardware structure and a software structure.Then,the measurement results of greenhouse environmental parameters are analyzed,and the radio energy model of the experimental system is given.Finally,an energy-efficient clustering algorithm for the greenhouse system is proposed.This clustering algorithm uses the core ideas of the multi-hop clustering algorithms based on the aggregator and AHP,namely cluster head rotation and data fusion.The experimental results show that the clustering structure of the greenhouse clustering algorithm has a characteristic of the periodic change.The reconfiguration of cluster heads can improve the fault tolerance and load balance of the system.Fixed clusters can employ the data aggregation method of average value,and can avoid communication interference between greenhouses.Moreover,the clustering algorithm of data aggregation is superior to the clustering algorithm of data forwarding and direct transmission in terms of the network energy dissipation in each round and the cumulative energy dissipation of the network.