Research Of Channel Estimation For The High-speed Railway Environment In LTE

With the rapid development of China's high-speed railway,the speed of high-speed railway is getting faster and faster,and a larger Doppler frequency offset will bring a huge challenge to channel estimation.The OFDM(Orthogonal Frequency Division Multiplexing)technology adopted in LTE(Long Term Evolution)is very sensitive to carrier frequency offset.Therefore in LTE,the research on channel estimation under high-speed rail transmission environment is particularly important.Aiming at the high-speed rail transmission environment,this thesis adopts the channel estimation method based on frequency offset estimation to reduce the impact of Doppler frequency offset.This thesis first introduces the technology of LTE downlink OFDM and uplink SC-FDMA(Single-carrier Frequency-Division Multiple Access),and introduces the frame structure of LTE.Then it introduces the high speed railway transmission environment,mainly including the multipath effect and the Doppler effect.The channel model of high speed railway environment adopts the multipath Rice channel model.This thesis introduces three common channel estimation algorithms,LS(Least Square)algorithm,DFT(Discrete Fourier Transform)algorithm and LMMSE(Linear Minimum Mean Square Error)algorithm,and two frequency offset estimation algorithms,CP-based frequency offset estimation algorithm and Moose frequency offset estimation algorithm,and analyses them via simulation.Then the thesis studies and analyzes the factors affecting the range of frequency offset estimation.On the basis of Moose algorithm,the pilot is adopted to estimate frequency offset and the pilot block is optimized.The frequency offset estimation is improved and verified by simulation under double pilot blocks and four pilot blocks.The results show that the improved method under double pilot blocks has better performance in low SNR(Signal Noise Ratio),and the improved method under four pilot blocks has the more precise estimation results.For downlink,this thesis analyzes the time domain and frequency domain interval of pilot structure,and the linear interpolation algorithm under different pilot interval is simulated and analyzed.For uplink,this thesis first introduces the uplink sub-carrier mapping,and adopts localized sub-carrier mapping method which has strong anti-frequency offset ability.In the study of uplink frequency offset estimation,this thesis adopts a method of changing the multi-user frequency offset estimation into single user frequency offsetestimation,and verifies its feasibility by simulation.Then this thesis introduces the uplink pilot structure,and analyzes the maximum mobile station speed that it supports,and the channel estimation results of each user are simulated and analyzed.The relevant parameters of the 5M transmission bandwidth in LTE are used to simulate the downlink and uplink respectively.The results show that the bit error rate of downlink and uplink is greatly reduced after adding frequency offset estimation.