Channel Estimation On Time-Varing Channels For LTE Systems

In recent years, the rapid development of the High-speed Rail calls for a high-level quality for Rail Communications. Especially with the popularity of fourth-generation public communications network (4G), the Research on wireless broadband communication systems in High-speed Rail field has become the current hot spots. In fast Time-Varying channel environment, accurate channel estimation techniques will become more important, especially for LTE systems which use MIMO-OFDM as the core technique. The thesis will research the Pilot Aided Channel Estimation in the Time-Varing channel Environment.In this thesis, the channel characteristics of wireless mobile systems and channel time dispersion and frequency dispersion parameters are introduced firstly. The problems and challenges the mobile communication confronts under the environment of High-Speed Rail are analyzed and the basic principles of OFMD and MIMO technology are introduced.In Chapter3,the MIMO-OFDM system simulation based on the3GPP link layer protocol TS36.211is simulated, and proved that the2by2antenna STBC OFDM system has a3dB lower in BER than the SISO-OFDM system by simulation. Then the pilot sequence which is formed by gold sequences and Zadoff-Chou sequences are researched and simulated. Then several channel estimation algorithms, including LS, LMMSE and SVD-LMMSE algorithm are discused. The receiver SNR estimation error’s effect on LMMSE is simulated and analyzed. The data position interpolation algorithms are researched, including Linear interpolation, Second order Polynominal Interpolation and Spline interpolation algorithm. At last the BER performance of different interpolation algorithms on channels with different delays in a single downlink sub-frame of LTE is compared and analyzed.In Chapter4,several BEM algorithms are introduced firstly. The effect which Doppler frequency shift and the BEM order numbers brings to the channel fitting performance of different BEM algorithms is discussed later, which is also proved by simulation. Then the Inter Carrier Interfenerce caused by fast fading channel is analyzed and the cluster pilot is used to eliminate the ICI in simulation. Then the principles of channel estimation by using BEM are discussed.At last, the performance of channel estimation using CE-BEM and DPS-BEM with cluster pilot in fast-fading channel is compared and analyzed.