Channel Estimation For Lte Downlink In High Mobility Scenarios

In LTE wireless communication system, the peak rate is required to be100Mbit/s for downlink and50Mbit/s for uplink. At the same time, due to the high mobility of user terminals. Doppler shift will have a significant increase, the channel state information will have a rapidly change in a short period. In a conclusion, it is very urgent to achieve the effective channel estimation with high mobility in time varying environment.First of all, the physical layer standard and related protocols of3GPP LTE downlink are introduced, OFDM and MIMO key techniques, wireless channel transmission characteristics including the modeling method of flat fading and frequency selective fading, influence of high mobility environments for OFDM and MIMO-OFDM systems are analyzed. Then the channel model of simulation is given.Secondly, a LTE downlink system simulation platform is constructed, the traditional channel estimation methods including LS, MMSE and SVD-MMSE, interpolation method in time and frequency domain and detection algorithm are introduced. The performance simulation of each algorithm is completed, it indicate that system bit error rate and mean square error of SVD-MMSE algorithm which based on MMSE algorithm is consistent, but it has a reduction in system complexity. Compared with the LS channel estimation method, both SVD-MMSE and MMSE algorithm performance better. It also shows that ML detection algorithm have the optimal signal detection performance but with a high complexity.Then, the basis expansion model for time-varying fading channels with high mobility are studied, some common BEMs are introduced including the complex exponential BEM. polynomial BEM, discrete cosine transform BEM, and KL-BEM based on the optimum criterion of mean square error. Based on the traditional complex exponential BEM, combing with the oversampling technology and modified CEBEM model, an improved model basis function is completed. The mean square error performance of all the base models are analyzed in this simulation.Finally, basis expansion models are applied to the LTE downlink system under the condition of time-varying fading channels with high mobility. The channel response in pilot OFDM symbols is estimated by LS, MMSE algorithm, Basis expansion models are used to track the time-varying channel response in a subframe and the bit error rate, mean square error performances are simulated. In the procedure of constructing the basis function of improved CEBEM, oversampling technology is applied which makes the frequency resolution increased. At the same time, modified CEBEM model is applied which makes the maximum fitting frequency equals to the maximum Doppler frequency shift, It is helpful to reduce the CEBEM fitting error. The simulation results indicate that improved CEBEM has a better performance than traditional CEBEM in bit error rate and mean square error.