Research On Channel Multiplexing Of The Train Communication System

ABSTRACT:With the rapid modernized development of rail vehicles and increasing requirements of reliability, safety and real-time for the control network of rail vehicles, the Multifunction Vehicle Bus (MVB) has become a communication bus standard for modern vehicles and forms a two-level bus of Train Control Network (TCN) together with the Wire Train Bus (WTB). Meanwhile, rapid development of on-vehicle information network (audio broadcasting, video monitoring, etc.) has proposed a much higher requirement for the bandwidth of the train communication system. Therefore, an object of this dissertation is to design and develop a more effective communication system without adding new communication lines while ensuring reliability of the existing control network with consideration of vehicle's spatial limitation and requirements for cost. Thus, there is proposed an idea of TC-PIS (Train Control Passenger Information System) in which additional multimedia information using OFDM technology is incorporated into the existing train control network to implement channel multiplexing of train communication system. Through the research of this task, it is helpful to solve technical problems faced with the combination of train control network and information network currently. The finished main work and the obtained novel results are as follows:1. Research of the MVB baseband transmission system. Analysis and research on a typical digital baseband power spectrum and bit error rate, On the basis of modeling and simulation of typical baseband signal power spectrum and research on Ethernet physical layer coding, a mathematical model of MVB code is established and a MVB frame head frequency spectrum function is deduced. Moreover, on the basis of further analysis and research on MVB telegrams, a MVB baseband signal power spectrum is calculated and simulated. Using a design of band-limited filter which can ensure normal safe operation of the baseband transmission system, at the same time which can reduces interference of the baseband signal on the high frequency carrier signal, thus optimizing the bandwidth of the MVB baseband transmission system.2. Research of channel characteristics of MVB transmission medium. This dissertation focuses on the MVB's physical layer media, analyzes its equivalent circuit and establishes its numerical model based on the traditional transmission line theory. The numerical model parameters of the MVB cable are deduced by using a least squares numerical fitting method, a RLCG numerical model is established, and frequency characteristics of R, L, C and G are simulated and analyzed, thus to obtain the cable's attenuation characteristics, characteristic impedance, available bandwidth, channel capacity and so on. Meanwhile, interference condition in the channel when the train is running is analyzed. Finally, the correctness of the model is verified by a large number of experiments on the MVB cable.3. Establishment of the TC-PIS simulation model. On the basis of MVB baseband transmission system and its channel characteristics, an OFDM-based TC-PIS system model is established, and an optimized synchronization algorithm for ML estimation method of G consecutive symbols based on adaptive correlation window is proposed with respect to the TC-PIS system.Signal simulation and analysis of each key point is performed in accordance with the designed parameters. As can be seen from the signal constellation and curve of BER, in case of keeping a certain SNR, the system can properly achieve modulation and demodulation of data and ensure rapid and reliable transmission of data. Furthermore, the anti-interference performance when the baseband and the carrier are transmitted simultaneously is researched and simulated based on this model, and through the optimized design of the parameters, no interference between transmission of baseband and carrier is ensured.4. A test platform satisfying the TC-PIS network experiment and test requirements is established, including a train control network and a train multi-media information system. On this basis, the TC-PIS prototype system is implemented, which includes three MVB devices and two OFDM nodes. The OFDM transceiver is implemented using FPGA, and a circuit enabling driving amplification and coupling is designed. After a front end EDA simulation verification is performed on the whole system, a board-level debugging is performed. Performance indexes of MVB control network and the TC-PIS system proposed in this dissertation are tested and analyzed through numerous simulation and test, to verify the correctness and feasibility of this research.At last, based on the summary of the research contents in this paper, thoughts and conclusions obtained during the research are presented, and some problems required to be further researched deeply are provided.