Research On TD-LTE Uplink Transmission Technology In High Speed Mobile Environment

In order to meet the high-speed data transmission services and needs,a new generation of long-term evolution of mobile communication system(LTE)came into being.The orthogonal frequency division multiple access(OFDMA)technology is applied for its downlink.The single carrier frequency division multiplexing(SC-FDMA)technology is applied for its uplink.The increase of Doppler frequency shift at high speed causes the channel to produce fast time-varying fading and destroy the orthogonality between subcarriers,which makes the performance of the system especially the uplink be seriously affected.Therefore,for the high-speed mobile environment uplink transmission system,the more in-depth study is carried out from two aspects of the Doppler frequency offset estimation technology and time-varying channel estimation technology in this paper.The main research work is as follows:Firstly,the research on the uplink channel is carried out.The high speed mobile transmission channel and the main factors influencing the performance of the uplink transmission system are analyzed.The high-speed rail channel model at home and abroad is given.The research on the channel transmission model of domestic high-speed rail in different scenarios is carried out.Then the time-varying channel model of the uplink transmission system is obtained.In addition,several major factors affecting TD-LTE uplink system performance are analyzed from two aspects of the same channel scene and different channel scene.Secondly,the algorithm of Doppler frequency offset estimation in uplink is studied.The algorithm of traditional frequency offset estimation is studied.An improved frequency offset estimation algorithm is proposed.In the high-speed scenario,the improved algorithm uses the method of combination of rough estimation and refinement.The auto regressive model is used to track the frequency offset estimates between subframes.Thus improving the accuracy of estimation,reducing the interference of noise and the complicated calculation degree.The improved algorithm is compared with the performance of the existing algorithm in simulation.The results shows that the improved algorithm have a better performance gain.Finally,the research on the time-varying channel estimation technique in the uplink is carried out.The existing channel estimation algorithm is analyzed.According to the shortcomings of the existing channel estimation algorithm,an improved algorithm is proposed,which was processed in the redefined domain.The parameter estimation of all symbols on the channel is obtained by the polynomial fitting method in the length of a subframe.The AR model with change tracking factor is used in the subframe to carry on the tracking processing.Thus the accuracy of the data symbol parameter estimates at both ends of the pilot symbol onthe channel is improved.Then the estimated data is changed from the transform domain to the frequency domain according to the transition relation between the channels.The obtained channel estimation response can be frequency-domain equalized.Simulation analysis and comparison of the improved algorithm and the existing algorithm system performance the advantages and disadvantages.The improved algorithm reduces the computational complexity of the system.So it is more advantageous.