| ABSTRACT:As the first proposed globally protocol, LTE has been widely applied in public communicaorithms under high-speed train scene, complying the TD-LTE standard series. In high-speed scene, the faster the moving station moves, the more the channel varies in time. Besides, the environments of transmitting waves is changing along with the movement of MS, and the channel becomes unstationary. Through simulation, it is advised that the current pilot patterns in LTE standards don’t sufficiently satisfy the demands of channel estimations, when the speed is high. What’s more, the Doppler shift causes the deviation of sub-carrier in frequency domain, decreasing the power of sub-carrier and increasing the inter-carrier interference. Above all, the importance of the estimation of Doppler shift is presented, and they are the cut-in points of the research of the Doppler shift estimation algorithm.The work and innovations of this thesis are listed as follows:Firstly, Doppler shift estimation algorithms in this thesis are categorized into calculation of the auto-correlation in time domain or the Doppler power spectral density in frequency domain. Three algorithms are supported with simulation in a LTE simulation platform.Secondly, the Doppler power spectral density plays an important role in Doppler shift estimation in frequency domain. I get familiar with the real scenes of railway, and analyze the channel characteristics and Doppler power spectral density of each scene.Thirdly, the downlink of LTE physical layer is based on OFDM technology, and many parameters like system bandwidth, frame structure, pilot patterns and so on are standardized in the LTE protocols. The LTE testing protocols offers two MIMO channels as reference:EPA model based on tap-delay-line model and ITU model which is an geometry-based stochastic model. The thesis analyzes the LTE simulation platform wrote in MATLAB language used in this thesis, and tests this platform according to the LTE testing protocols.Fourthly, we use an suitable channel model to simulate the real channel, in order to revise or verify the Doppler shift estimation algorithms in the high-speed railway scenes.To sum up, these three Doppler shift estimation algorithms are offered and verified under the condition of TD-LTE standards, high-speed railway scene and MIMO. The simulation offers markable reference to the network design and optimization for the specific railway communication network at high speed. |
