Research On Wireless Channel Modeling And Link Simulation Of Train-ground Communication In CBTC System

Communication based train control (CBTC) is an advanced system in the world subwaysignal control systems, and it uses the wireless local area network technology which bases onthe IEEE802.11protocol to achieve the train-ground communication. Wireless channel andlink performance directly affect the train-ground secure data communication performance. Itnot only requires big consumption of manpower and resources to test wireless channelcharacteristic by using the field measurement method, but also is difficult to measure. So thethesis sets up a corresponding wireless channel model by using actual wave transmissioncharacteristics, and designs link simulation process on the basis of IEEE802.11g standard offraming, then train-ground communication channel is simulated under the different operatingenvironments and different transmission mediums. The simulation results show that leakagewaveguide transmission performance is superior. The main research contents are as follows:Firstly, the model is considered from large-scale fading and small-scale fading, and thethesis adopts the method of tunnel environment factor correction to model the free wave pathloss in the tunnel environment, and establishes the tunnel small-scale model by using themulti-path effect, finally the free wave tunnel environment model is received. It uses a singlegap on leakage waveguide which is equivalent to magnetic dipole, and the electromagneticwave propagation loss in the leakage waveguide is introduced. Then the model of subwaytrain-ground communication leakage waveguide model is established.Secondly, in view of the IEEE802.11g protocol which the train-ground communicationwireless local area network adopts, according to the agreement in the framing process andusing MATLAB simulink communication toolbox, it designs CBTC train-groundcommunication link process. The channel includes the established tunnel environmentfreedom wave model and leakage waveguide model.Finally, the accuracy of the tunnel environment free wave model and leakage waveguidemodel are tested, at the same time the simulation process of link validity is tested. Thecorrectness of the models simulation results is compared with measured values and theoreticalcalculation values. Link simulation design correctness is tested by the results of the simulationerror rate and the theoretical value of test method is given in the related literature. Correcttunnel environment free wave model and leakage waveguide model are introduced into theCBTC link simulation process which have been completely designed, then freeelectromagnetic wave block error rate in different operating environments and linktransmission performance in different transmission medium are obtained.Simulation data indicate that leakage waveguide transmission block error rate of thesubway train-ground wireless communication system is lower than the electromagnetic wave transmission both in the open spaces and tunnels. If train-ground wireless communicationemploys free electromagnetic wave, the block error rate in electromagnetic wave transmissionin tunnel is higher than that in the open environment.