HYBRID LS-LMMSE CHANNEL ESTIMATION Technique for LTE Downlink Systems

In this paper, we propose to improve the performance of the channel estimation for LTE Downlink systemsunder the effect of the channel length. As LTE Downlink system is a MIMO-OFDMA based system, a cyclicprefix (CP) is inserted at the beginning of each transmitted OFDM symbol in order to mitigate both intercarrierinterference (ICI) and inter-symbol interference (ISI). The inserted CP is usually equal to or longerthan the channel length. However, the cyclic prefix can be shorter because of some unforeseen channelbehaviour. Previous works have shown that in the case where the cyclic prefix is equal to or longer thanthe channel length, LMMSE performs better than LSE but at the cost of computational complexity .In theother case, LMMSE performs also better than LS only for low SNR values. However, LS shows betterperformance for LTE Downlink systems for high SNR values. Therefore, we propose a hybrid LS-LMMSEchannel estimation technique robust to the channel length effect. MATLAB Monte –Carlo simulations areused to evaluate the performance of the proposed estimator in terms of Mean Square Error (MSE) and BitError Rate (BER) for 2x2 LTE Downlink systems.