| 3GPP implements LTE project for new air interface and radio access network standardization in order to be competitive in the area of broad-band radio access in the next l 0 years.LTE improves the performance of cell edge users, increase cell capacity and lower latency.The scheme of multiple access using in LTE downlink is orthogonal frequency division multiple access (OFDMA). The biggest merit of OFDMA is the ability to resist frequency- selective fading, simultaneously can raise the frequency spectrum efficiency effectively. Accurate channel estimation is the key to the high transmission performance and ensures the superiority of the system. So this thesis is engaged in the research of channel estimation technology for LTE downlink OFDMA system.The channel estimation algorithms for LTE downlink OFDMA system are introduced in detail.Channel estimation technique for OFDM based systems can be grouped into two main categories:blind and non-blind.The non-blind channel estimation with pilot-symbol-aided is studied.Two kinds of basic channel estimation algorithms,the Least Squares(LS)channel estimation algorithm, and Linear Minimum Mean Square Error(LMMSE)channel estimation algorithm are described.Combined with the system features and some of the existing channel estimation algorithm, two kinds of effective channel estimation algorithm are analyzed compared in this thesis. The one is channel estimation algorithm based on dominant channel taps and the other is LMMSE iterative filtering channel estimation algorithm. Then this thesis gives a principle describes of both algorithms in detail and explains the steps of both algorithms. In LTE downlink OFDMA system, the performance curves of both algorithms with different channels, different modulation schemes, under various scenarios are analyzed in detail. Simulation results show that within the limited increase of conditions complexity, both algorithms are effective to improve the accuracy of channel estimation and improve BER performance. |
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