Doppler Frequency Shift Estimation For High Frequency Spectrum In High-speed Railway Scenario

Nowadays,the global system for mobile communications for railway(GSM-R)is a digital wireless communication system which has been widely used in China.However,with the development of Internet,the requirements of passengers for mobile communication are extended from the original voice communication to high broadband service,including video telephone and online multimedia.GSM-R can not meet the demand of data service from train passengers due to its narrow-band characteristic.Therefore,a new generation of high-speed railway wireless communication system is necessary.The International Union of Railways(UIC)has proposed that 3G technology is not suitable for the railway system,while the Long-Term Evolution(LTE)proposed by 3 GPP has a strong performance advantage over the 3G system in data rate,latency,coverage and downward compatibility.Therefore,LTE is introduced to be the next communication systems for railways,which is often referred to as LTE-R(LTE-Railway).In the high-speed railway scenario,the relative speed between trains and base stations can be as high as 360 km/hour,much larger than the regular train speed 120 km/hour,which gives rise to the severe doppler frequency shift phenomenon.And the orthogonal frequency division multiplexing(OFDM)system is exploited in the downlink of LTE which is sensitive to the doppler frequency shift.The doppler frequency shift can damage the orthogonality of the subcarriers,which will result in serious inter-carrier interference(ICI),and hence affect the performance of OFDM.In addition,the millimeter-wave is a research hotspot in recent years,which can support higher order of bandwidth and capacity.If the millimeter-wave is applied into the high-speed railway,which inevitably will lead to more serious doppler frequency shift.Therefore,how to solve the estimation and correction of doppler frequency shift is of great significance to the development of LTE-R and the promotion of millimeter wave.The doppler frequency offset model is similar to the carrier frequency offset model under the assumption of coherent demodulation operated between the receiver and transmitter.And there have been many methods for carrier frequency offset estimation,which can be applied into the doppler frequency offset eatimation model.Therefore,we firstly conclude four classical carrier frequency offset estimation algorithms:the maximum likelihood estimation algorithm,the estimation algorithm based on cyclic prefix,Moose algorithm and SC algorithm.In the paper,according to the different introduction of doppler frequency shift,two types of channel modeling for high-speed railway are carried out based on the rician channel model.Then we compare and analysis the four estimation algorithms from operation time,estimation range and estimation performance in LTE system.The performance difference is also explored under the viaduct,cutting and tunnel scenario.As a conclusion,the Moose algorithm performs best and has a stable estimation performance in three scenarios.Finally,to further improve the performance of the Moose algorithm for strong LOS scenario,we utilize the correlation between the parameters at different time intervals in the same position on the railway.Due to the doppler frequency offset only has impact on the main path of the channel model in strong LOS scenario,firstly we extracted LOS path information of the signal through the channel estimation.Then the improved algorithm based on Moose is proposed by using the historical measurement information as a prior information.Based on the theoretical derivation,the simulation result shows that the improved Moose algorithm performs better than the original Moose algorithm.