Analysis And Simulation Of Wireless Interference In CBTC System

With the development of train operation control technology, CBTC (CommunicationBased Train Control) has been widely used in urban rail transit. Train-ground Bi-directionalCommunication System is an important part of the system, it transmits data using WirelessLAN technology that takes IEEE802.11as a standard. The Wireless Standard works in the openISM band, so the train-ground communication processes are disturbed by other air waves. Inorder to guarantee the system reliability and train operation safety, it is significant to analyze theinterference problem of the system.Firstly, the paper described the system structure and data communication subsystem ofCBTC combing with the802.11standard, including wireless network structure, data flowdirection and wireless devices, etc. On this basis, the paper analyzed the influence of overlappedsignal to the system, viewing on the outside interference, as well as the affect of the insideinterference from the basic access angle.Secondly, the thesis analyses the model of transmission of wireless, the Large-scale fadingprocess during wireless transmitting in the air, as well as two distribution patterns of thesmall-scale fading signal, Rayleigh distribution and Rice distribution. According to the mode offree space loss and the special circumstance of CBTC, construct wireless propagation Modelapplying to wireless environment of urban rail transit was constructed, and interference factorsfrom different channels were analyzed with the help of MATLAB to ensure the accuracy ofsimulation results.Finally, according to circuit diagram of Xi’ an Metro Line1, the different train operationsenses are built by OPNET. Firstly, network module was built with working parameters,such asmovement path,data flow, communication protocol, etc. Then different train operation séanceswere built to analyze and simulate CBTC system suffering interference from both outside andinside. The results show that transmission between train and ground was interfered by otherradio wave, especially when the train began roaming switch, the phonograph becomes muchobvious, interference decreases as channel spacing increases, but never disappear, meanwhile,the influence of the interference eliminated by increasing the transmit power of CBTC.