Analysis On Communication Parameters Effect On Cbtc Systems Using Opnet

To a large extent, wireless communication affects the performance of the train control system of CBTC. Up to now, there are more studies on GSM-R of railway than those on WLAN (Wireless Local Area Network) of mass transit. In addition, there is no such study about the relationship between train control accuracy and train ground communication performance. For this reason, this thesis analyses the major performance of train ground communication, which influence the train control system. Firstly, the requirements of CBTC on wireless communication are analysed. Secondly, some parameters of the wireless communication system of CBTC are analysed. Furthermore, the major communication parameters in CBTC is designed based on the CBTC requirement. To some extent, these studies may be used for practice.Based on the characteristics of the wireless channel in CBTC, Qos of communication is analyzed. The performance metrics includes:transmission error, continuous packet loss, and interruption time of handoff. The interruption time requirement of CBTC on the interruption time is also analysed. A rational threshold of the interruption time is given.The major parameters of train ground communication system in CBTC is designed in this thesis. The wireless propagation loss model in tunnels is refined based on the simulation results and field measurements. Combined with other many other factors, a suitable interval between AP is suggested. Through GE model, the statistic of continuous packet loss is analyzed, and point out that the main reason that influence the number of continuous packet loss is level passing rate and average duration of fading. The whole process of handoff and the major factors influencing the handoff time is analyzed in the thesis. The handoff time in different circumstances is obtained from field measurements.Using the OPNET simulation tools, the thesis construct a whole train ground communication system simulation model in CBTC based on 802.11g. Based on this model, the thesis simulates the performance of the train-ground communication system under the train control trafic. It also analyze the train ground communication's effect on train tracing operation with the simulation model and the relative parameters derived before.