| Wireless sensor network is the network system which is made of a number of sensor nodes with the capabilities of perception, calculation and wireless communication. It has the characteristics of high practicality, a wide range of applications and flexibility. Furthermore, it is a forefront research topic with the highly multidisciplinary cross. So its key technology research and development is the hotspot in the current field of study, and time synchronization technology is one of them.At present, the single hop time synchronization algorithm research has already become mature. However, the research about multi-hop time synchronization algorithm is relatively weak. The existing algorithm can’t meet the requirement in practical application of wireless sensor networks because of its own features and the unpredictable environment of application. So this article, based on the analysis of the error, applies the thought of clumps to application environment of the high density and large scale sensor networks, and then puts forward a new time synchronization protocol.We firstly analyze the research dynamic of time synchronization technology at home and abroad, and then compare some existing algorithms of time synchronization. On top of that, we give the reason why time synchronization protocols for traditional network do not apply to wireless sensor network and demonstrate the deficiency of existing algorithm. Then, this paper analyzes the synchronization error of TPSN, which is one of typical protocols for wireless sensor networks. We point out the influential factors of synchronization errors and establish the mathematical model of synchronization errors. Then we show that one-hop synchronization errors also meet normal distribution under the condition of considering all the time delays, and also give the random process model of the multi-hop for the maximum errors of wireless sensor networks and its expectation, variance and the upper and lower limit. The simulation experiment verifies the validity of the results. Finally, based on the analyze of time synchronization error, this paper proposes a time synchronization protocol based on exponential delay for clustery wireless sensor networks, which utilizes the improved algorithm of LEACH protocol to select the first node, and topology of breadth-first spanning tree to choose the members of cluster. The protocol combines pair-wise synchronization mechanism and the synchronization mechanism which uses probability theory to compensate the clock drift and the clock offset. Synchronization is divided into two stages of the synchronization between the base and the cluster heads and the synchronization within clusters. In the previous stage, it adopts two-way synchronization technology. However, in the latter stage, this paper considers the exponential delay to compensate the clock offset and the clock drift. It is proved in theory and by evaluation experiment that the estimation of clock offset is synodical. The performance analysis and experimental results of the protocol show that the overhead is little and the synchronous precision is high.Time synchronization problem of wireless sensor network also involves routing technology, positioning technology, and other key technology. In the future, comprehensive experiment is needed to conduct. In addition, we can use the protocol to the practical monitoring environment after verifying the availability in hardware experimental platform. |
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