Research On Railway Time Synchronization Technology Based On LTE-R

With the rapid development of high-speed railways and the rapid improvement of train speed,ensuring the real-time and accurate transmission of train control information on the railway wireless communication system is crucial to the safety of train operation.The existing GSM-R wireless communication system for railways uses the NTP protocol to achieve time synchronization.However,due to its own bandwidth and transmission rate limitations,the GSM-R system cannot adapt to future railway development needs and needs to evolve to LTE-R.At the same time,as the speed of trains continues to increase,the system’s requirements for synchronization accuracy are also gradually increasing,and the problem that NTP protocol is difficult to meet the accuracy requirements is becoming increasingly prominent.Therefore,in order to achieve high-precision LTE-R time synchronization,this article starts with the characteristics of LTE-R train-to-ground wireless channel and communication link,as well as the technical characteristics of LTE-R train-to-train communication,and studies the time synchronization process between LTE-R train-to-ground and train-to-train equipment based on the PTP protocol.The main research work of the paper is as follows:(1)Aiming at the problem of LTE-R multipath fading,Doppler frequency shift,and other channel characteristics,PTP packets in the existing methods will have uncertain delay jitter in the transmission process,resulting in large master slave clock skew error and poor stability in the compensation process,an LTE-R time synchronization method based on the Kalman filter algorithm is proposed.Firstly,this method introduces Bernoulli random variables to establish a state space model of master-slave clock offset,uses the Kalman filtering algorithm to obtain the optimal estimate of clock offset error under LTE-R,and then uses the frequency compensation method to achieve clock phase offset compensation,thus achieving the time synchronization process between master and slave clocks under LTE-R.Finally,simulation experiments show that the proposed method has higher synchronization accuracy and better stability.(2)Aiming at the impact of link congestion and resource scheduling on the time synchronization process,the synchronization information transmission rate and transmission delay are prone to jump,resulting in poor synchronization accuracy,an LTE-R time synchronization method based on differential autoregressive moving average ARIMA model is proposed.Firstly,the asymmetry ratio of transmission rate is introduced to establish a clock model for high-speed railways,and the theoretical and actual time series of railways are obtained.Afterward,the actual time series is used as model input and the ARIMA model is used to complete the prediction compensation of the sequence.Finally,through the corresponding simulation experiment,it is verified that the proposed method has higher synchronization accuracy.(3)Aiming at the problems of current train-to-train time synchronization methods that are susceptible to packet loss,resulting in low synchronization accuracy and slow convergence speed,a train-to-train time synchronization algorithm based on model predictive control(MPC)is proposed.Firstly,an observer equation is introduced to construct an MPC-oriented state space model for front and rear train clocks.Secondly,the optimal clock offset control amount is obtained through the MPC controller.Then,time synchronization of different train-to-train communication scenarios is achieved through continuous iteration.Finally,simulation experiments under different train-to-train communication scenarios demonstrate that the proposed method has a faster convergence speed.