Quasi-Decorrelating Detector (QDD) - A Study on New Algorithm for CMDA Multiuser Detection

本文主要是介紹一種應用於CDMA多用戶檢測的技術(multi-user detection scheme)：Quasi-Decorrelating Detector (QDD)，這種多用戶檢測技術的系統性能可以非常接近Decorrelating Detector (DD)但是他的系統架構卻較為簡單，QDD主要是利用多項式來取代反矩陣，而此多項式是由相關矩陣R所衍生而來的，經由串聯多級的matrix filter來達到反矩陣的目的。 在本論文中主要探討QDD在實際的通道環境中的系統性能之表現，由於通道環境是隨著時間而有變化的，因此在QDD系統中可藉由改變matrix filter串聯的階數來應付通道環境的變化。我們考慮到了基本的上傳 (uplink)與下傳 (downlink)，所謂的上傳是指行動台(mobile station)把信號傳送給基地台(base station)，而下傳則剛好相反是基地台傳送訊號給行動台，並且我們考慮到了實際通道中存在的多重路徑效應，我們假設可分辨的多重路徑數目為一定值，並且有一個衰減增益 (path gain)存在於每一個路徑上，在本文中也討論了使用RAKE接收機來分別為相等增益合成器 (equal gain combining)與最大比率合成器 (maximal ratio combining)來克服多重路徑效應的影響，由實驗曲線證明了RAKE接收機可以有效的改善系統在遭遇了多重路徑效應的性能。We propose a multi-user detection scheme for downlink channel and uplink link channel, including multi-path effect. The Quasi-Decorrelating detector (QDD) is a linear detector but the decorrelating algorithm is performed without inverse matrix transform, as an effort to overcome the problem associated with the DD. The QDD can be implemented by multi-stage feed-forward filters, the number os which can be made scalable to trade MAI suppression for noise enhancement reduction according to varying channel conditions. On the contrary, the DD has a rigid structure and is unable to adapt to changing operation environment. For downlink channel, we considering the multi-path and fading effect, and we assume that there are 12 kinds of channels to simulation. To improve the system performance, two different types of RAKE receiver structures, equal gain combining RAKE and maximum ratio combining RAKE, are also considered for CDMA systems to mitigate multi-path fading effects of mobile channels. For uplink channel, the assumption are the same with downlink channel, the different is just the users are asynchronous each other.中文摘要......................................................i 英文摘要.....................................................ii 誌謝........................................................iii 目錄.........................................................iv 圖目錄.......................................................vi 表目錄.....................................................xxii 第一章 導論...................................................1 1-1 研究動機................................................1 1-2 論文架構................................................3 第二章 多用戶檢測系統.........................................4 2-1 概要....................................................4 2-2 Decorrelating Detector..................................4 2-2-1 DD之系統架構........................................5 2-2-2 DD之性能分析........................................6 2-3 Decorrelating Decision-Feedback Detector................7 2-3-1 DDFD之系統架構......................................8 2-3-2 DDFD之性能分析.....................................10 2-4 Improved Decorrelating Decision-Feedback Detector......11 2-5 Orthogonal Decision-Feedback Detector..................13 2-6 Improved Orthogonal Decision-Feedback Detector.........16 2-7 系統性能比較...........................................18 第三章 使用QDD演算法之同步CDMA多用戶偵測系統.................23 3-1 概要...................................................23 3-2 多重路徑通道下同步CDMA系統使用QDD演算法之架構分析......26 3-3 QDD的硬體實現架構......................................44 3-4 同步CDMA系統使用QDD演算法之性能分析....................44 3-5 當訊號延遲非整數倍Tc時的QDD系統........................49 3-6 DD與QDD之複雜度分析與比較..............................55 3-7 結果與討論.............................................58 3-8 效能曲線與分析.........................................59 第四章 使用QDD演算法之非同步CDMA多用戶偵測系統...............92 4-1 概要...................................................92 4-2使用於非同步CDMA系統之QDD演算法.........................93 4-2-1 非同步CDMA系統使用QDD演算法之架構分析..............93 4-2-2 QDD演算法之效能分析...............................101 4-3 在多路徑通道下使用QDD演算法之非同步CDMA系統...........104 4-3-1在多路徑通道下非同步CDMA系統使用QDD演算法之架構分析105 4-3-2在多重路徑通道下QDD演算法之效能分析................111 4-4 當訊號延遲非整數倍Tc時的非同步QDD系統.................114 4-5 結果與討論............................................120 4-6 效能曲線與分析........................................121 第五章 結論與建議...........................................136 5-1結論...................................................136 5-2 QDD與PE的異同.........................................138 5-3建議...................................................139 參考資料....................................................14