| The rapid development of mobile communications today, LTE systems have appeared in a variety of commercial systems. Orthogonal frequency-division multiplexing(OFDM) as a mainstream technology LTE systems. It has a strong anti-inter-symbol interference(ISI) and the ability to decline and many other advantages. OFDM access to data information at the receiving end by coherent detection techniques, therefore, in order to recover the transmitted signal, accurate channel state information is estimated become an essential part. High-speed rail technology matures,mobile users high-speed mobile communication systems under a higher requirement. Train moving at high speed, the signal severe fading, the channel becomes fast varying channels, LTE system as the current mainstream commercial system, how to give a precise estimate of the channel face more severe challenges. Therefore, this study focused on the LTE wireless communication system based on high-speed mobile environment channel estimation techniques.First, this paper introduces the wireless channel characteristics and simulation models,focusing on analysis of the current main channel estimation method based on pilot-assisted, in two steps: first, containing reference OFDM symbol estimates signal, there is the least squares(LS),least minimum mean square error(LMMSE) and improved SVD algorithm, given simulation comparison. Conclude that, in the low SNR, LS algorithm is simple, lack of precision, high SNR,due to the floor effect, LS performance but compared to good effect.Subsequently, the paper fast time-varying characteristics of the channel for high-speed travel.Focuses on basis expansion model(BEM), and improved base for several common complex exponential basis expansion model and the base(CE-BEM) over-sampled complex exponential base(OCE-BEM) normalized mean square error simulation comparison. Conclusion, OCE-BEM model fitting performance is always better than the CE-BEM, overall, the best performance for DKL-BEM and DPS-BEM two models.Finally, given the complex exponential basis expansion model(CE-BEM) has spectral leakage problem. Combined with windowing technique to suppress the influence of the Doppler shift, get windowed complex exponential base(ICE-BEM) model. Combined with the estimated coefficient mapping orthogonal transformation to obtain windowed oval base(IDPS-BEM) model, to further improve the estimation accuracy. Simulation and comparison, further proof windowed basis expansion model performs better estimation accuracy has been improved. Next, the group extendedmodel in the LTE system, the pilot OFDM symbols used at LS and select the channel response estimate LMMSE two algorithms, a sub-frame in the time domain OFDM time-varying channel response using the base extension model fitting, simulation the BER different mobile speeds.Conclusion, first of all depend on the estimated position of the pilot selection algorithm, therefore,LMMSE estimation method is always better than the estimation method based on LS-based, the same algorithm, oval base model performance is better than complex exponential base model. |
