Study Of Time Synchronization Method In Wireless Sensor Network

Wireless sensor network (WSN) is a self-organizing network that combines sensor technology, information processing technology and network communications technology, which is widely used in data acquisition, data processing and communication. The application of WSN involves national defense, environmental monitoring, industrial control, smart home, etc. It widely attracted the focus of the people in the industry and academia circles since its appearance. As a key technology, time synchronization is essential in a WSN when facilitating groups of applications, such as sensor localization, data aggregation, distributed sampling, source localization, etc. Usually, data which lack of time in the practical application is meaningless. Therefore, the study of time synchronization technology is of great significance to the application and development of WSN.To solve the problem of high overhead and unbalanced energy consumption that caused by exchanging majority of messages for a higher accuracy in typical algorithms, as well as the drawback of high frequency of synchronization operation in typical algorithms, two algorithms are proposed on the basis of classical synchronization algorithms. They are energy-balanced and low-overhead time synchronization algorithm, and energy-effective and adaptive time synchronization algorithm. Because wireless sensors are typically designed with very stringent constraints for size, cost, and especially power consumption, both algorithms focus on the efficient energy usage in the network.The energy-balanced and low-overhead time synchronization algorithm for wireless sensor networks is designed as follows:Based on a hierarchical topology, cluster heads accomplish the synchronization process by pair-wise message exchange mechanism with the Sink node, and adopt maximum likelihood estimation for the clock offset and skew correction, thus get a high accuracy as well as decrease the times of the synchronization process. Linked with broadcasting properties and remaining energy, cluster members synchronized to their cluster head by adopting pair-wise packet exchange and reference broadcast mechanism, thus reduce numbers of transmission packets and balance the energy in the network. The experimental results show that the proposed algorithm relatively has a less packet cost and balances the energy consumption while guarantees the node's precision, and extends the network's life.The energy-effective and adaptive time synchronization algorithm for wireless sensor network is designed as follows:Based on the clustering topology, the algorithm is divided into time synchronization phase and re-synchronization period adjustment phase. In the first phase, the cluster head synchronizes the reference node with a SR mechanism, while the cluster members synchronize the reference node with a RO mechanism by listening to the packets that transmitted by the cluster head. The packets coming from the cluster head contain the time information generated in the last round of synchronization. As a result, the phase reduces the communication overhead greatly. Moreover, the algorithm adopts the maximum likelihood estimation for the clock offset and skew correction, which gets a good precision. In the second phase, the cluster head estimates the cluster synchronization error and regulates the re-synchronization period dynamically according to the accuracy requirement as well as estimates the optimal number of synchronous message in every synchronization period, thus reduces numbers of unnecessary synchronization. The experimental results show that the proposed algorithm reduces the synchronous frequency, and guarantees the energy efficiency with meeting the request accuracy.