Research On Common Cable Communication Transceiver For Monitoring Track Circuit Based On Spread Spectrum Technology

The safe and reliable operation of railway signal equipment and system affects the safety of passengers and running efficiency.As we all know,the railway along the complex and diverse environment,such as wet,dry,strong electromagnetic conditions.In this environment,various signal devices are distributed.In order to monitor and manage these devices,signal monitoring system is introduced on the spot.The existing signal monitoring system and monitoring equipment are basically confined to the station,in the process of signal transmission needs separate cable or uses other equipment of the standby cable core.In recent years,relevant departments found that after the failure of interval signal equipment,because it was not included in the monitoring system,most of the time was wasted in the process of fault diagnosis.Thus,a lot of time and cost are wasted on the maintenance of interval signal equipment.Therefore,this thesis adopts track circuit digital cable to transmit monitoring signal,which can effectively bring the equipment within 4 km along the line into centralized management.Through studying spread spectrum communication technology and digital communication technology,it is applied in the signal transmission of railway signal monitoring system,The digital communication and spread spectrum communication technology are used to effectively improve the anti-interference ability of the transmission system.Firstly,SPT digital track circuit cable is used to transmit the monitoring information of outdoor equipment.In this process,the digital communication and spread spectrum communication technologies are studied,and the advantages of the digital technology over analog technology are analyzed.Considering the difficulty of implementation,the Direct-sequence spread spectrum communication method is chosen to realize the transceiver research.In order to realize the long-distance transmission of signals and improve the channel utilization,the QPSK carrier modulation technology is chosen,and its channel utilization is doubled compared with BPSK.Secondly,the synchronization mechanism of spread spectrum communication system is analyzed basing on the previous research.By changing the structure of acquisition and tracking loop,the time of acquisition and tracking process is shortened,and the probability of false alarm is reduced by the cooperation of six correlators,so that the acquisition process is efficient and reliable,and the algorithm is simple.The loose tail ring structure is further Improved to be suitable for spread spectrum and carrier synchronization.Compared with Costas Ring,the hardware resource of the Improved loop is reduced by 20%.Then analysis the symbol synchronization technology system,and explain the implementation process.After that the characteristics of track circuit cable and spread spectrum communication system are analyzed.Finally,the communication system is designed by programming on FPGA,and the common-cable system is tested with 4km track circuit cable.When the signal is transmitted in4 km cable,it can reliably receive the status information from the outdoor equipment.Then analysis the voltage values of some nodes in the track circuit with or without superposition monitoring,and the parameter values in the shunt state.The test results show that the transceiver can transmit the monitoring signal well and can’t affect the normal pick-up and drop of GJ.