長期演進技術(LTE)是第四代移動通訊的重要技術其中之一。此技術於下行鏈路系統使用正交頻分多重存取(OFDMA)的技術,它是基於正交分頻多工(OFDM)技術改良而來。OFDM技術可以非常有效的改善頻譜使用率,但它對都卜勒效應和頻率偏移非常敏感。因此,OFDMA技術就像OFDM一樣,需要解決因為環境的影響從而導致子載波間正交性的破壞,以及載波間相互干擾(ICI)等問題。 本篇論文著重於LTE下行鏈路系統的通道估測研究。因為在LTE下行鏈路系統的參考信號的是網格型,所以使用幾種二維內插法來做為通道估測方法。這些方法包括:最近相鄰、雙線性和雙立方內插法。這些方法會在各種通道環境下進行模擬比較,包括延長行人模型(EPA),擴展車輛模型(EVA)和擴展典型城市模型(ETU)。這些通道模型分別代表為低、中、高延遲擴展環境。模擬結果與比較會在各種通道環境呈現。由這些模擬結果,我們可以發現在一般通道下雙線性內插法具有更好的性能,因此,我們可以採用此種相對簡單的內插法,用於LTE 的下行鏈路系統的通道估測。
Long term evolution (LTE) technology is one of the most important transmission schemes for fourth-generation mobile communications. This technique for downlink system uses orthogonal frequency division multiple access (OFDMA), which is based on orthogonal frequency division multiplexing (OFDM). OFDM technology can increase spectral efficiency, but it is quite sensitive to the Doppler spread and frequency offset. Therefore, OFDMA technology like OFDM scheme, has to address the influence of environment, thereby causing the failure of orthogonality among the sub-carriers and inter-carrier interference. This thesis focuses on channel estimation in LTE downlink systems. Because the kind of reference signal in LTE downlink system is grid type, several two-dimensional interpolation schemes are investigated for channel estimation. These schemes include nearest, bilinear and bicubic interpolation methods. These methods would be compared in various channel environments, including extended pedestrian A model, extended vehicular A model and extended typical urban model. These channel models are selected to be the representatives of low, medium and high delay spread environments. As a result, some comparative simulations are presented under various channel environments. By these simulation results, we find out that the bilinear interpolation has better performance in general, so we can apply this relatively simple method for channel estimation in LTE downlink system.
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