On Cluster-Based Hierarchical Time Synchronization Of Wireless Sensor Networks

The availability of cheap micro sensors and low power wireless communication enabled Wireless Sensor Networks (WSN)'s extensive applications in the real world. WSN can detect, monitor and eventually control many real-world problems. Accurate time is needed both in WSN applications and many networking protocols. WSN have clear different requirements of time synchronization in the aspects of time correctness, time precision and energy consumption meeting different technologies and applications. Therefore, it's necessary to research new time synchronization protocols adapting to different WSN.The thesis researches cluster-based time synchronization protocol. Cluster-based topology is widely used in the organization of WSN, which is easy for managing and extending networks and consumes low power.Firstly, time synchronization development and its necessity are studied. Time synchronization techniques are described respectively corresponding to one-hop and multi-hop time synchronization categories. The weaknesses of these techniques are also demonstrated comparing to cluster-based networks. Then a new cluster-based time synchronization protocol-Delayed-Hierarchical Time Synchronization (DHTS) is proposed. The paper deduces synchronization errors of this protocol and testifies the protocol's good performance. By simulation, This paper compares plane and cluster-based topology DHTS protocols, the result shows the superiority of cluster-based topology; One-hop nodes'ratio range is estimated to guarantee the protocol's good performance; The paper compares the DHTS protocol with DMTS protocol and HRTS protocol in the aspects of energy consumption and synchronization errors, the results testifies the superiority of DHTS protocol, and cluster headers'ratio is estimated; This paper also compares energy consumption of cluster headers in different node density networks. The result proves that the cluster headers'energy consumption is increased geometrically with the node density's increase.In the static cluster-based DHTS protocol, Cluster headers consume too much power, and nodes'power load is not balanced. To solve this problem, this paper proposes one dynamic cluster-based DHTS protocol. A new cluster header election algorithm is proposed in the base of LEACH protocol. Then synchronization errors of the dynamic cluster-based DHTS are deduced. Computer simulation compares synchronization errors and energy consumption between dynamic and static cluster-based DHTS protocol. The result shows that dynamic cluster-based DHTS protocol outperforms the static one and the performance improvement is much more visible with more circles of cluster header election.In addition to meeting network requirement of synchronization precision, dynamic cluster-based DHTS protocol can also save energy of the whole network and balance nodes load. It can be easily applied to the real world.