Research On Time Synchronization Algorithms Of Different Topological Structures In WSN

Wireless Sensor Network (WSN) which integrates sensors, embedded computing, networking and wireless communication technologies is the current research hotspot of concern. As a key supporting technology of wireless sensor networks, Time synchronization is not only necessary for normal operation of the applications of wireless sensor networks, and the synchronization accuracy directly determines the quality of other services. However, the characteristics of WSN itself challenge to the design of time synchronization algorithms. Therefore, the study of developing time synchronization algorithms suitable for WSN has attracted wide attention. This thesis does in-depth study aiming at the existing time synchronization algorithm for WSN. The main works are as follows:Firstly, this thesis briefly introduces wireless sensor networks, describes the basic principle of time synchronization, and then some of the existing time synchronization algorithms for sensor networks are classified,deeply analysed and compared.Secondly, different applications in sensor networks use different topological models. On the basis of considering the requirements on the energy consumption and synchronization precision and the shortcomings of existing algorithms, in view of tree topology in sensor networks, a spanning tree-based energy efficient time synchronization algorithm for WSN (TETS) is proposed. The algorithm combines the advantages of TPSN, RBS and tiny-sync / mini-sync algorithm and makes full use of broadcasting features of the radio channel based on CSMA and the discipline of clock linear drift. It combines the sender-receiver and receiver-receiver mechanism to achieve the network synchronization on the basis of tree topology. While clock drift of nodes are estimated and compensated, the logical clocks are constructed to avoid the sudden change of the node clocks. The simulation results show that the TETS algorithm has the advantages of low communication overhead, high precision synchronization and quick synchronization convergence rate.In addition, for the characteristics of cluster topology of the sensor networks, this thesis proposes a cluster-based energy-efficient time synchronization algorithm for WSN(CETS). The CETS algorithm is based on the clustering topology which is formed by using LEACH algorithm. It completes synchronization of the entire network by the cluster-inter and cluster-intra synchronization phases. In the cluster-inter phase, it adopts the pair-wise packet exchange mechanism to finish the time synchronization between the sink node and cluster heads through dynamically establishing a hierarchical structure. In the cluster-intra phase, it finishes the synchronization between cluster heads and cluster members by the combination of the sender-receiver and receiver-receiver mechanism. At the same time it constructs logical clocks of cluster members to estimated and compensate the clock drift to improve the synchronization accuracy and maintain the continuity of the clock. The simulation results show that the CETS algorithm has advantages in saving energy and improving time synchronization precision.Finally, the thesis gives the summary of the entire contents and points out the direction of future work.