臺灣博碩士論文加值系統

正交分頻多工(Orthogonal frequency-division multiplexing, OFDM)結合多根傳送多根接收天線是應用在高速無線傳輸大有可為的技術。然而，當使用者設備在高速時，嚴重的載波間干擾(intercarrier interference, ICI)將會破壞OFDM信號的正交性，致使系統性能下降。由載波間干擾通道矩陣的分析得知，ICI效應的有效界限在以中心子載波往外兩邊有限子載波。本論文中，我們提出雙邊決策回授等化器(BD-DFE)來消除行動多入多出正交分頻多工(MIMO-OFDM)系統之載波間干擾效應。BD-DFE由上下兩部份等化器所組成，上半部份使用決策回授等化器得到暫時之訊號預估值，下半部份則利用雙邊決策回授等化器來消除雙邊的載波間干擾而得到最後訊號偵收。在這樣作法下，雙邊的載波間干擾會消除更徹底。模擬結果顯示，我們提出之接收機於移動 OFDM系統在性能和複雜度間提供了良好的平衡。

Orthogonal frequency division multiplexing (OFDM) combined with multiple transmitter and receiver antennas (MIMO) is a promising technique for high-speed wireless transmissions. However, severe intercarrier interference (ICI) coming from high mobility of user equipment corrupts the orthogonality of the OFDM and pulls down the system performance. From the analysis of the ICI channel matrix, it is revealed that the interference can be effectively bounded in finite double-side subcarriers centering the desired subcarrier. In this paper, we propose bi-directional decision feedback equalizer (BD-DFE) to tackle ICI problem for the mobile MIMO-OFDM system. The equalizer consists of two-part equalizers. The upper part uses DFE to output tentative decisions. The lower part employs BD-DFE aiming to cancel both pre- and post-cursor ICI to give a finial symbol estimates.
In so doing, double-sided ICI can be removed more completely. Simulation results show that our proposed receiver for the mobile OFDM system provides good tradeoffs between receiver performance and computational load.

目錄

摘要 I
ABSTRACT II
誌謝 III
目錄 IV
圖目錄 V
表目錄 VI
縮寫字 VII
數學式符號 VIII
第一章　緒論 1
1.1　 研究動機 1
1.2　 論文架構 2
第二章　快速通道對MIMO-OFDM系統之影響 3
2.1 多重路徑效應和都普勒效應 3
2.2 時變通道模型 5
2.3 功率延遲輪廓 6
2.4　MIMO-OFDM系統架構 7
2.5　 載波間干擾通道矩陣 8
第三章　雙邊決策回授等化器 15
3.1　接收機設計準則及DFE架構 15
3.2　利用ICI通道矩陣稀疏性特性降低運算複雜度 22
3.3　 MIMO-BD-DFE演算法 25
3.4 訊號與干擾雜訊比(SINR) 29
第四章　模擬結果 30
4.1　 MIMO-OFDM(A)於多路徑快速衰減環境下之系統效能 30
4.2 運算複雜度分析 35
第五章　結論 36
參考文獻 37

圖目錄

圖2.1　黑色線為可視線，虛點線為反射效應，虛線為散射效應，點線為繞射效應多重路徑示意圖 3
圖2.2 多重路徑的影響 4
圖2.3 指數衰減脈衝通道 7
圖2.4 MIMO-OFDM 系統架構 8
圖2.5 循環前置示意圖 9
圖2.6 載波間干擾矩陣 H 13
圖2.7 頻率錯誤導致訊號振幅減少 14
圖3.1 分數間距等化器架構圖 16
圖3.2 DFE架構圖 19
圖3.3 (a) FFF架構圖 20
圖3.3 (b) FBF架構圖 20
圖3.4 2 2 MIMO-OFDM在fd =0.05下通道矩陣3D能量圖 23
圖3.5 H 通道矩陣示意圖 23
圖3.6 MIMO-BD-DFE 接收器架構圖 26
圖4.1 載波分配方法(a)subband CAS,(b) interleaved CAS,(c)generalized CAS 31
圖4.2 BD-DFE與FIR-MMSE-FEQ、MMSE-DFE比較，在fd=0.05下錯誤率效能32
圖4.3 BD-DFE與FIR-MMSE-FEQ、MMSE-DFE比較，在fd=0.1下錯誤率效能32
圖 4.4 BD-DFE比較D={1、2、3}，在fd=0.05下錯誤率效能 33
圖 4.5 BD-DFE比較D={1、2、3}，在fd=0.1下錯誤率效能 33
圖 4.6 BD-DFE比較D={1、2、3}，在OFDMA系統有fd=0.05下錯誤率效能 34
圖4.7 BD-DFE比較D={1、2、3}，在OFDMA系統有fd=0.1下錯誤率效能 34


表目錄
表4.1 模擬實驗之參數設定 30
表4.2 複雜度比較在MIMO-BD-DFE, FIR-MMSE-FEQ[1]和MMSE-DFE[4] 消除技術, 在 N = 64 , NT =NR= 2, D=1, 和 Q=NT(2D+1) = 6 35

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