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標題: 正交迴授判決檢測器
Orthogonal Decision-Feedback Detector (ODFD) for CDMA Multi-user Detection
作者: 吳昇銓
Wu, sheng-quan
關鍵字: Orthogonal Decision-Feedback Detector (ODFD);耙形接收器;多路徑效應;正交迴授判決檢測器;RAKE receiver;multipath effect
出版社: 電機工程學系
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):Orthogonal Decision-Feedback Detector (ODFD),這種多用戶檢測技術的系統性能可以非常接近Decorrelating Decision-Feed-back Detector (DDFD)但是他的系統架構卻較為簡單,ODFD主要是利用了一組matched filter bank來接收訊號,而這一組matched filter bank的sequence是利用對展頻碼做Gram-Schmidt orthogonalisation procedure 所產生的,ODFD演算方法只有做Gram-Schmidt orthogonalisation procedure的步驟需要處理,ODFD的好處也包括了舊的用戶離開或新的用戶進入系統時系統的matched filter bank係數不需要重新計算仍可使用,如此一來可以減少很多的計算次數,而在matched filter bank的輸出端則使用了successive decision-feedback detection來檢測訊號,這個部分則和DDFD相同。在本論文中主要探討ODFD在實際的通道環境中的系統性能之表現,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,模擬結果與理論推導均證明了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 orthogonal decision-feedback detector (ODFD) employs a match filter bank matching to a set of orthogonal sequences, which are generating by Gram-Schmidt orthogonalisation procedure based on spreading codes. The ODFD algorithm involves only the orthonormal coefficient matrix, which require no frequent recalculations even when system parameters change. Successive decision-feedback detection is performed immediately at the output of the ODFD match filter bank without the transform matrix, which requires in the DDFD. 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. And in this thesis we comparison structure and algorithm complexity between ADDFD and AODFD.
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