Time Synchronization Technology Research For Coal Mine Gas Concentration Monitoring System Based On WSN

As a special self-organizing distributed network, Wireless Sensor Network(WSN) can not only solve the problem of complex structure cabling, high cost and poor flexibility of the wired network but also can combine with the wireless gateway devices, bringing about an extensive application prospect in the networked disaster monitoring system based on the Internet of Things(Io T). Early warning mechanism should be adopted to predict the gas disaster which is one of the most serious mining disasters. The methane accumulations always happen in the face tunnel. There is instant correlation among the gas density, spatial position and time. In view of the time synchronization in the underground gas density monitoring system based on WSN, on the basis of analyzing the research background, the existing study of time synchronization at home and abroad and the existing time synchronization techniques, this thesis conducts main study as follows:(1) By analyzing the rule of gas diffusion and migration in the underground roadway and mining workface, a linear banded network communication model is adopted in the mine laneway and a topological structure based on the grid is adopted in the special gas emission location in the workface respectively in the thesis.(2) In view of the linear banded model in the roadway, the thesis puts forward a new algorithm—ILHTS which is appropriate for the time synchronization algorithm of the gas density monitoring in the mine laneway. The ILHTS algorithm can be divided into two steps, adjacent cluster synchronization and inner cluster synchronization. In the adjacent cluster synchronization, the hierarchical structures between the clusters’ head nodes are constructed whose synchronization with the Sink nodes is realized by bidirectional information exchange. In the later step, the synchronization between the inner cluster nodes and the head nodes is realized by one-way synchronization mechanism based on the Bayes estimation algorithm to satisfy the time precision and reduce the whole power consumption of the network. The simulation results show that the range of time precision is hundred microsecond level theoretically as well as the power consumption is reduced by order of magnitude.(3) In view of the grid structure adopted by the mining workface in the limited heterogeneous space, an improved I-HRTS algorithm is designed in the thesis by adopting the Maximum Likelihood Estimation(MLE) of the clock frequency offset and phase offset on the basis of the original algorithm. The simulation results show that accumulative error of time precision is improved theoretically. It does not increase the power consumption of the algorithm but improves the synchronization precision to satisfy the requirements of gas density monitoring better.The research results in the thesis can not only satisfy the requirements of time synchronization in the mining underground gas monitoring system but also reduce the energy consumption in the synchronization process and expand the application of WSN in gas monitoring on the premise of meeting time synchronization precision.