在以直接序列展頻(Direct Sequence Spread Spectrum, DSSS)技術為基礎的直接序列-分碼多重接取(Direct Sequence-Code Division Multiple Access, DS-CDMA)系統中，限制系統效能的主要因素便是系統的干擾阻絕能力(Capability of Interference Rejection)。再此系統中，多用戶接收機(Multiuser Receiver)一般分為兩大類，第一類稱為集權式接收機(Centralized Receiver)，因為它必須知曉所有使用者的資訊，包括每位使用者的展頻碼、訊號所受到的通道效應等等，由於運算複雜，所以這類的接收機比較適合應用在基地台端。第二種多用戶接收機則稱為分權式接收機(Decentralized Receiver)，因為它僅需知曉目標使用者的某些資訊即可，故適合應用在行動端。分權式接收機亦可進一步區分為兩類：外加資料式(Data-Aided)及非外加資料式(Non-Data-Aided)接收機。一般非外加資料式接收機又稱為盲蔽式接收機，吾人所提出的干擾消除器便是屬於此類。
本論文主要是探討吾人所提出的盲蔽式干擾消除器在各種狀況下的效能表現。在此干擾消除器中，具有一新穎的干擾偵測器(Interference Detector)，可有效偵測強干擾。當強干擾存在時，接收信號便會通過干擾阻絕轉換器(Interference-Blocking Transformer)，利用子空間的方式來濾除強干擾。經過干擾阻絕轉換之後的訊號，只需利用傳統的解展頻技術便可獲得目標資料。在本論文中，除了對此干擾消除器有完整的數學分析外，吾人並利用電腦模擬來觀察其在不同狀況下的效能表現。經由電腦模擬的結果顯示，此干擾消除器在各種狀況下均有不錯的效能，並且具有低複雜度的特性，非常適合應用在行動端。在本論文的最後，吾人為此盲蔽式干擾消除器做一個結論，並期許未來能以此技術發展更完善的多用戶接收機。

In the direct sequence-code division multiple access (DS-CDMA) system, which uses direct sequence spread spectrum (DSSS) technique to perform multiple-access, the major limitation of the system capacity is the capability of interference rejection. In this system, multiuser receivers usually divided into two groups, the first group is called the “centralized receiver,” because it must know the information of total users, including the spreading sequence of each user, channel response, etc. Due to the complexity of computation, this kind of receivers is suitable for the base station. The second group is called the “decentralized receiver,” because it only needs to know the information of desired user, therefore, it is very suitable for mobile station. The decentralized receiver can be further separate into two kinds: data-aided and non-data-aided receivers. Usually, the non-data-aided receiver is also called the blind receiver; our proposed interference cancellator belongs to this blind one.
This thesis mainly discusses the performance of our proposed interference cancellator in different conditions. There is a novel interference detector which can efficiently detect strong interferers in our proposed interference cancellator. When strong interferers exist, the received signal will be passed through the interference-blocking transformer, which exploits the subspace approach to block strong interference. After interference cancelled, conventional de-spreading technique is used to obtain the desired data. In this thesis, besides the complete mathematical analysis of our proposed interference cancellator, computer simulations are also used to observe its performance behavior in different conditions. The simulation results exhibit that this interference cancellator has good performance in different conditions, and due to have the property of low complexity, our proposed interference cancellator is very suitable for the mobile station. Finally, we make a conclusion for this blind interference cancellator, and expect to realize a mature multiuser receiver based on this technique in the future.

Blind Subspace-Based Interference Cancellator for the Downlink Receiver in DS-CDMA System

Chapter 1 Introduction

Chapter 2 CDMA System Overview
2.1 Model of Spread Spectrum Digital Communication System
2.2 Pseudo-Noise Sequence
2.3 Direct Sequence Spread Spectrum Signals
2.4 Multiple Access Technique
2.5 Wireless Communications: Cellular Radio System
2.6 Multipath and Doppler Effects
2.7 Classification of Small-Scale Fading Channel
2.8 CDMA Wireless Communication System
2.9 Summary

Chapter 3 Interference Cancellation for the Downlink Receiver in DS-CDMA System
3.1 Signal Model of the DS-CDMA System
3.2 Some Important Techniques for Blind Interference Cancellation
3.3 Proposed Blind IC System
3.4 Define the Decision Factor
3.5 IB Transformation and Detecting Desired Data
3.6 Improve the Subspace approach
3.7 Drive the MSE of the Subspace Approach
3.8 Future Work: Application for SIC-Based Power Control

Chapter 4 Computer Simulations
4.1 Simulation Parameters
4.2 Single-path Environment
4.3 Multipath Environment
4.4 The Influence of Velocity

Chapter 5 Conclusion

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