Research On Multi-band Frequency Direct Communication Technology Between Trains

Ensuring the reliability and security of train operation is the top priority in the railway system.In recent years,with the rapid development of high-speed railway and the increase of train speed,the demand of emergency communication and redundant communication in railway system is becoming greater.Ultrashort wave direct communication system has been designed by our research group so as to implement the direct communication between trains in plain environment by using vehicle-carried communication devices.Based on the previous study,it is extended to multiband direct communication system which can adapt to plain environment and tunnel by working in different frequency bands,and its communication performance in tunnel environment is studied.The main contents are as follows.Firstly,for the application of direct communication technology in tunnel,the appropriate working frequency is determined.Then a kind of multiband transmitter and receiver applied in direct communication among trains are designed.The proposed transmitter and receiver can work in ultrashort wave frequency band in plain environment and millimeter wave frequency band in tunnel.The sensitivity of the proposed receiver under the millimeter wave frequency is calculated.The direct communication between trains in tunnel is achieved.Secondly,combining with the tent law,the propagation mode and multipath effect of electromagnetic waves in tunnel,the deterministic models of direct communication channel in single and double line railway tunnel are established.The simulation results show that the reflection rules of electromagnetic waves in tunnel can be realistically described by the deterministic models.Based on these rules,the multipath effects which are generated by reflection of electromagnetic waves in tunnel can be analyzed accurately.Consequently,the propagation delay and the signal attenuation caused by the difference of phases and amplitudes among different paths during the propagation can be calculated.Then considering the random problem of the envelope of received signal in tunnel,the statistical model of direct communication channel between trains is established.The corresponding channel characteristics of built model are obtained as follows: when there are direct paths between trains,the communication channel is the Rice fading channel with certain range of visibility.Otherwise,it is the Rayleigh fading channel.Finally,on the basis of the established deterministic model and statistical model,the wireless channel is estimated by assisted pilot based channel estimation method.Then GMSK modulation method is selected for the designed communication system.The corresponding simulation models in both Rayleigh and Rice fading channel are established in Communication System Toolbox of MATLAB Simulink.The changing situation of bit error rate with various SNR is simulated in different fading channels.At the same time,in order to observably reduce the bit error rate of communication system,the LDPC is selected to code the channel.Then the corresponding bit error rate is simulated in MATLAB.The simulation results show that the bit error rate is reduced observably after coding the communication channels.