Research And Performance Analysis On OFDM System In The High-speed Railway Scenario

With the fast development and deployment of High-Speed Railway(HSR)in China,the demand for wireless broadband access under HSR scenario has increased.Orthogonal Frequency Division Multiplexing(OFDM)is one of the key technologies in fourth generation mobile communication(4G),Orthogonal Frequency Division Multiplexing is an attractive multi-carrier modulation technique which has some advantages with anti-multipath fading,make full use of spectrum resources and so on.The research aiming to apply OFDM to HSR scenario has received more and more attention in recent years.Doppler shift caused by high speed and complex electromagnetic environment pose serious challenges to channel estimation and channel modeling.Therefore,in view of the above problems,this thesis mainly includes:(1)This thesis researches the characteristics of the radio channel under the HSR scenario and detailed analyses Inter-Carrier Interference(ICI)of OFDM system.This thesis also studies the the insertion mode of pilot and the pilot-assisted channel estimation algorithms.In order to solve the problem that the DFT-based interpolation algorithm cannot suppress the nosie in the channel impulse response within the length of cyclic prefix,this thesis presents an improved DFT interpolation algorithm,this improved DFT interpolation algorithm can depress the nosie of CIR within the length of the cyclic prefix by using Threshold value,then through iterations,inter-carrier ICI and noise are further suppressed.Simulation results are provided to corroborate our proposed studies.(2)In view of the fast time-varying wireless channel in the HSR scenarios,this thesis researches the Basis Expansion Model(BEM)channel estimation algorithm,In order to reduce the influence of ICI on pilot position and improve the accuracy of the basis function coefficients,the clustered pilot structure is applied to this thesis.Considering the spectrum efficiency,we optimize the structure of pilot cluster according to the analysis of ICI.In order to further improve the accuracy of channel estimation,this thesis presents a Basis Expansion Model combined Discrete Fourier Transform(DFT)channel estimation algorithm,ICI coefficient term is obtained by BEM channel estimation,and then by improved DFT interpolation algorithm to eliminate noise and recover the channel state information.Simulation results are provided to corroborate our proposed studies.(3)This thesis researches the OFDM system performance under different HSR scenarios.Firstly,we model the wireless channel by using the Tapped Delay Line theory and the channel data obtained from different HSR scenarios.Then combined with the channel estimation algorithm and channel model studied in this thesis,we use MATLAB to build OFDM simulation system.In the simulation,this thesis studies the relationship between OFDM system throughput and Signal-Noise-Ratio(SNR),it also researches the impact of different channel estimation methods and different areas on the OFDM performance.