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標題: QDD - 一種新型的分碼多工多用戶訊號偵測演算法之研究
Quasi-Decorrelating Detector (QDD) - A Study on New Algorithm for CMDA Multiuser Detection
作者: 周代偉
Chou, Tai-Wei
關鍵字: Multiuser Detection;多用戶偵測;Decorrelating Detector;去相關偵測器
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):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.
Appears in Collections:電機工程學系所

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