The Design And Simulation Study Of A Safetv-critical Communication Protocol Applied In CBTC

Safety and reliability are the permanent theme of the train control system. In CBTC system, the punctual and reliable data communication is the precondition and foundation of the safe train operation. It’s the safety-critical communication protocol that has the most direct relationship with the safe data transmission. This paper designs a safety-critical communication protocol with relatively perfect functions for the safety-critical data transmission in CBTC and studies the elementary characteristics of the protocol using OPNET Modeler.In the protocol design process, the demands on the safety-critical data transmission given by CBTC system is analyzed first. Then, with a full understanding of the requirements to safety measures that are addressed in EN50159and supposed to be applied in the safety-critical data communication, the safety-measures and the data transmission process of the protocol are specified.In order to carry out the protocol simulation in OPNET Modeler, the switch between different wireless access points for mobile stations is realized through adding codes to the wireless module of OPNET Modeler and the protocol logic is translated to the finite state machine model. For the network modeling, the network topology of Shenyang subway1is taken into account and the connection features of the dual-duplex safe computer are simulated in the application layer.Finally, the effects on the average delay that the packet sending interval and the packet size have are studied through the analysis of the simulation results. The average delay has little relationship with the packet sending interval, which indicates the safety measures of the protocol won’t result in overloaded system consumption. Though the average delay would increase with the growth of packet size, the growth range is still within the CBTC application requirements. While in the past researches, the fault-injection function of OPNET Modeler has been seldom focused on. To verify the fail-safe function and the robustness of the protocol, a link failure is introduced and a packet loss scenario as well as a delay scenario are created. The simulation results show that the protocol well satisfies the real-time response requirements and has a certain fault-defense capability. So it can be applied in CBTC system.