Research On Channel Estimation Of LTE-Advanced System In High Mobility Wireless Environment

In recent years,with the rapid development of high-speed railway and highway,the communication demand in high mobility wireless scenarios is also increasing.In addition,it requires more on some indicators,for example,demanding higher quality on communication and system capacity.Meanwhile,under the rapid development of mobile communication system,Long Term Evolution-Advanced(LTE-A)system has been widely deployed.LTE-A adopts orthogonal frequency division multiplexing(OFDM)as a multi-carrier transmission scheme,in which the channel is divided into a plurality of orthogonal sub-channels.It can effectively eliminate the inter symbol interference,improve spectrum efficiency,simplify the design of channel equalization module.However,the wireless channel varies constantly under the high mobility wireless environment which leads to the decrease on the accuracy of channel estimation.Furthermore,the relative motion of the transmitter and receiver will introduce Doppler frequency offset(DFO),which will destroy the orthogonality among sub channels of the OFDM system,generate inter carrier interference(ICI)and damage the overall performance of the communication system.Therefore,in high mobility wireless environment,how to improve the accuracy of channel estimation and reduce the impact on ICI have become an important factor affecting the performance of LTE-A system.This thesis mainly studies how to improve the accuracy of channel estimation and receiver performance of the LTE-A system in the high mobility wireless environment.Firstly,we study the small scale fading characteristics of wireless channel,focusing on the statistical characteristics and time-varying characteristics of wireless channel,typical Doppler power spectrum and other key parameters.Then we analyze the system principle,transmission function,pilot structure of the OFDM system and the challenges it faces in high mobility wireless environment,and make the high-speed railway(HSR)scene as a typical high mobility wireless environment,introduce its characteristics and network architecture.Secondly,aiming at the deficiencies of the conventional frequency domain channel estimation algorithms in the high mobility wireless scenarios,we propose an extended U-type spectrum channel estimation algorithm and a channel estimation algorithm combined with DFO estimation.The former uses U-type to simulate the Doppler spectrum in the high mobility wireless scenarios and estimate the width of the Doppler spectrum,and the latter estimates DFO of each path.Both of them can generate the frequency and time channel correlation more accurately,thus improving the accuracy of channel interpolation and filtering,and reducing the channel estimation errors.In addition,simulation analysis of various frequency domain channel estimation algorithms is carried out to verify the performance gain of the proposed algorithm.Finally,in the high speed mobile environment,we study the time domain channel estimation of OFDM system based on the basis expansion model(BEM).We introduce the widely used BEM,analyze its modeling errors in HSR scenarios,then propose a joint ICI cancellation channel estimation algorithm,which can effectively reduce the influence of ICI on channel estimation and system performance by two iterations interference cancellation.Simulation results show that the proposed algorithm can effectively reduce the channel estimation errors and improve the system performance of the receiver.