Study On Doppler Shift Estimation And Compensation Of High Speed Railway In GSM-R System

With the rapid development of C hinese high speed railway in recent years,wire communication system puts out high requirements for the quality of service.Doppler shift and the time-variation of wireless channels caused by high-speed train increases bit error rate(BER)of the wireless communication system,the BER affects efficiency of data transmission and voice quality on mobile station of t he Chinese Train Control System(CTCS).According to Doppler shift and the time-variation of wireless channels,a combined estimation model of Doppler shift based on the in-vehicle information is proposed,and the improved Fitz algorithm is applied to this model.Simulation model of error rate for wireless channel transmission is constructed,by using the simulink toolbox of Matlab to simulate the error rate,and the simulation for improved Fitz is completed in high speed railway scenario.The results show that the proposed estimation algorithm can accurately estimate Doppler shift,there is a less error between estimates and true value.After correcting the Doppler shift,that can meet the allowed range of frequency shift in receiver,improve the demodulatio n performance of the receiver.The main contributions of this dissertation are as follows :(1)To derive calculation formulas of Doppler shift,as the train run under the conditions during straight and curve driving.In either case,by analyzing the horizo ntal distance between train and base station influences on the BER of GSM-R system,the randomness of BER is bigger during the curve driving,most of present algorithms don't effectively track carrier now,a combined estimation model of Doppler shift based on the in-vehicle information can solve this problem.(2)The model of BER of GSM-R system is given,analyzing Rician K-factor influences on systematic BER.When the Rician K-factor is different,by simulations and comparisons the performance of Kay algorithm,improved LCR algorithm and improved Fitz algorithm,compared with other two algorithms,improved Fitz algorithm is characterized by higher precision and bigger estimation range.It then analyzes the error of Doppler shift estimation algorithm in actual high-speed scenarios.The results show that improved Fitz algorithm estimation error is minimum compared with Kay algorithm and improved LCR algorithm,GSM-R system is a comprehensive wireless communication platform of high-speed railway,applied to Doppler shift estimation of GSM-R system of high-speed railway.(3)Doppler shift compensate structure based on station is derived.The BER of GSM-R system is analyzed through the simulation under different speed,after frequency compensation,the BER of GSM-R system is significantly reduced,that can satisfy the high-speed railway communication requirement,the overall throughput of system is improved.