Pilot Design And Channel Estimation In LTE Systems

In order to keep the durative competitive power of the mobile communication,3GPP has proposed its long term evolution (LTE) system to improve the performances, which apply the OFDM and MIMO etc.In combination with the key technologies of the LTE downlink physical layer and MATLAB modeling, this thesis is engaged in the research on the channel estimation technology for the LTE downlink and its performance in single cell or multi-cell environments.Firstly, based on the background and the current study situation of the LTE system and channel estimation, this thesis discusses the basic principles and the structure of MIMO-OFDM systems. The performances of block pilots and comb pilots in different channel conditions are simulated and analyzed, and the channel estimation algorithm, such as LS, MMSE and LMMSE, are also derivated and simulated. The simulation results indicate that the block-pilot scheme is less susceptible to the influence of the Doppler frequency shift and the comb-pilot scheme is less susceptible to the influence of the maximum multipath delay, and the simulation results also show that the LMMSE algorithm and the MMSE algorithm are better than the LS algorithm and the MMSE algorithm has a higher complexity.Secondly, based on the analysis of LTE TS36.211 protocol, we divide the channel model of the LTE downlink system, including scrambling module, modulation module, layer mapping module and precoding module. Through the introduction of the frame structures, the orthogonal design principle and selection of pilots in LTE system, a RS structures with 4 antennas MIIMO is determined. The thesis also discusses three interpolation algorithms, such as constant interpolation, linear interpolation and second-order interpolation, whose performance in the case of comb pilots are simulated and compared. Simulation results show that the Gaussian interpolation is better than the linear interpolation and the Constant interpolation. But the Gaussian interpolation has a higher complexity; the Gaussian interpolation is slightly better than the linear interpolation.Finally, the thesis respectively analyzes the performance of the channel estimation for the LTE downlink system in the environment of single cell and multi-cell. In the case of single cell environment, simulation resultes show that the diversity gain increase with the number raise of antennas, so as to improve the signal-to-noise ratio of the received signals, reduce the bit error ratio. Considering the case of cell interference, the process of generation and insertion of multi-cell pilots is analyzed. The FDM multiplex of the multi-cell pilots is realized by using cell specific movement. Simulation resultes demonstrate that the MMSE channel emulation is better than the LS channel emulation, either in single cell environment or multi-cell environment. Besides, the MSE performance of multi-cell is worse than single cell, for the reason of the interference of multi-cell environment.