首先回顧DS-CDMA系統中適應性去相關偵測器(adaptive decorrelating detector)的方法.此方法的目的是為了提升CDMA系統的表現,並藉由減少用戶間之干擾以增加系統用戶容量.在給定的背景資訊下,為達到此目的本篇論文考慮的方法為多用戶接收器.適應性演算法增加了此接收器的可行性.因此CDMA系統中,適應性多用戶接收器的方法已被提出以增加系統容量.適應性去相關器的使用可以減少來自於未知用戶間之干擾,雖然它將會增加雜訊的影響.然而,這個接收器基本上是被設計在CDMA系統於加成性白高斯雜訊(AWGN)同步傳輸之通道環境.為了證實其於非同步傳輸情形之穩健性,我們呈現了在微細胞架構下,當用戶間之傳輸時間延遲小於一個符號時段及當通道特性為多路逕瑞雷(Rayleigh)衰減下之實驗模擬結果.去相關偵測器除了在[1]中有效率的被實現外,它還可以結合決定迴授(decision feedback).連續干擾消除(SIC, Successive Interference Cancellation)的方法是藉由從接收到之信號減去巳偵測之較可靠訊號來延展.我們在頻率選擇(frequency-selective)多路逕瑞雷衰減環境中,提出一個去相關耙式接收器(decorrelating RAKE receiver)和決定迴授結合的方法.為了證實其即時運行之潛力,我們以電腦模擬結果來評估此接收器之表現.

A review of adaptive decorrelating detector techniques for direct-sequence code division multiple access (CDMA) signals is given. The goal is to improve CDMA system performance and capacity by reducing interference between users. The techniques considered are implementations of multiuser receivers, for which background material is given. Adaptive algorithms improve the feasibility of such receivers. An adaptive multiuser receiver for CDMA system has been proposed to increase system capacity. The adaptive decorrelator can be used to eliminate interference from known interferers, though it is prone to noise enhancement. However the receiver is basically designed for synchronous CDMA over AWGN channels. In order to confirm the robustness of the receiver for the asynchronous cases, experimental evaluations are displayed when the relative user delays are small compared to the symbol duration and when the channel is Rayleigh multipath fading as in micro-cellular scenarios. In addition to the efficient implementation of the decorrelating detector of [1], the receiver also can be adapted to incorporate decision feedback. Successive interference cancellation techniques reduce interference by cancellation of one detected signal from another. And an efficient incorporation of decorrelator with RAKE and (DF) decision feedback receiver for frequency-selective Rayleigh fading multipath channels is also proposed. Performance evaluation of the detector via computer simulation scenarios is conducted to substantiate it's potential for real-time operation.

Abstract………………………………………………………………………………………...I
Contents……………………………………………………………………………………….II
List of figures and Tables...………………………………………………………………….IV
Chapter 1 Introduction.………………………………………………………………………1
Chapter 2 Concept and Techniques of Multiuser Detection………………………………..4
2.1 Introduction……………………………………………………………………...……4
2.2 The CDMA System Model and Detection Method…………………………………...5
2.3 Liner Receiver………………………………………………………………………..10
Chapter 3 Adaptive Decorrelating Multiuser Detector for CDMA Systems
3.1 Introduction………………………………………………………………………….14
3.2 Adaptive Multiuser Receiver in AWGN Channel…………………………………...15
3.2.1 Adaptive Decorrelating Detector …………………………………………...16
3.2.2 Incorporation of Decision-Feedback and Adaptive Decorrelating Detector…22
3.3 Adaptive Multiuser Receiver in Multipath Fading Channel………………………....26
3.3.1 Adaptive Decorrelator with RAKE Receiver……………………………….31
3.3.2 Incorporation of Decision Feedback and RAKE Receiver…………………...31
Chapter 4 Computer Simulation Result…………………..………………………….35
Chapter 5 Conclusions………………………………………………………………………50
References……………………………………………………………………………………51

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