Research On The Clock Accuracy For Train Communication Network Based On Ethernet

At present, train communication network based on Ethernet has become the trend of future TCN. While the weakness of the traditional Ethernet in real-time and certainty, has affect the Ethernet Application in control field. To achieve high precision clock synchronization between different nodes is the premise and basis of guaranteeing Ethernet in real-time. After studying about the factors of Ethernet communication in real-time and certainty, this paper puts forward the clock synchronization solution with least square method, on the experiment platform, analyses the factors of influencing clock precision, and then put forward the solution. The main contents and innovative points include the following aspects:1、 Through the analysis and comparison the topology structure, communication mechanism, real-time performance of the train communication network based on Ethernet, this paper obtained feasible switched Ethernet based on star topology structure, and analyses the necessity of clock synchronization.2、 According to the Ethernet Real-time Communication requirements, this paper introduced IEEE1588precision clock synchronization protocol. Through analyzing the principle of the topology structure, protocol realization and message types of precision clock synchronization protocol, PTP, this paper put forward progressive compensation algorithm with least-squares of the clock synchronization, and analyses two possible way of least-squares clock compensate, which solved "sudden change"、offset enlarge and the difficulty of selecting time compensation value etc. in the clock synchronization processing, and then on the use of MATLAB modeling analysis, this paper proved the rationality and the feasibility of the algorithm, at last obtained the satisfactory simulation results.3、The research designed and built an experimental platform with the two kind of data acquisition node, which was based on AVR and ARM, and then transplanted real-time operation system, TCP/IP protocol stack and PTP synchronization protocol stack on base of the hardware design. Through theoretical analysis, mathematical calculation, the actual experiment, this paper realized clock synchronization method on improving Ethernet real-time communication, which is least square compensation method. And the precision is limited in200ns, which meet the requirements of train communication network. 4、Combining with the experimental data and theoretical analysis and calculation, this paper intensively analyzed the factors of influencing Ethernet clock synchronization precision, with the prominent problem of crystals drift, mathematical model and algorithm, this paper puts forward some practical solutions like the clock crystals drift compensate with FPGA, synchronous optimization algorithm, frequency compensation algorithm and so on, greatly improve the accuracy of the clock synchronization.