寬頻分碼多工存取系統之適應性線性最小均方差耙狀接收器

Abstract

本論文主要針對第三代行動通訊（寬頻分碼多工存取）系統中耙狀接收機之架構及原理做整體的研究，並探討數種演算法在快速衰減之通道中的效能及其對扺抗通道估側不準確時所造成的影響。傳統的耙狀接受器(Rake Receiver)在傳送高速資料速率時碼錯誤率並不會隨著訊雜比的增加而有顯著的改進，其效能會飽和而限制了系統的容量，在此，我們利用適應性訊號處理演算法來解決這個問題，並提出一改良式最小均方差耙狀接收器，以降低複雜度及提昇效能。

This thesis proposes a modified adaptive LMMSE algorithm to significantly improve the performance of the rake receiver in the case of high data rate situation, while reducing computational complexity, compared with conventional approach. The modified LMMSE algorithms also lead to a more stable convergence performance. The thesis also extensively studies the rake receiver, which is an important component in the third Generation Mobile Communication (Wideband Code Division Multiple Access) systems. Chinese Abstract i English Abstract ii Acknowledgment iii Contents iv List of Tables vii List of Figures viii Chapter 1 Introduction 1 1.1 Concept of CDMA 1 1.2 Rake Demodulator 2 1.3 Organization of this thesis 3 Chapter 2 System Description 5 2.1 W-CDMA System Overview 5 2.1.1 Physical Channels 6 2.1.1.1 Uplink Frame Structure 6 2.1.1.2 Downlink Frame Structure 7 2.1.1.3 Common Pilot Channel 8 2.1.2 Uplink Spreading and Modulation 9 2.1.2.1 Spreading 10 2.1.2.2 Channelization codes 12 2.1.2.3 Long Scrambling codes 13 2.1.2.4 Short Scrambling codes 15 2.1.3 Downlink Spreading and Modulation 17 2.1.3.1 Spreading 17 2.1.3.2 Channelization codes 18 2.1.3.3 Scrambling codes 18 2.2 W-CDMA Design Concept 20 2.3 System Model 23 2.3.1 3GPP Test Environment 24 2.3.2 Channel Fading Model 25 2.3.3 Transceiver Model 27 Chapter 3 Adaptive Rake Combining Algorithm 31 3.1 Rake Receiver 31 3.1.1 Diversity Combining 32 3.1.2 Maximal Ratio Combining 35 3.2 Limitation of the Conventional Rake Receiver 36 3.3 Multiuser Detection 37 3.4 Precombining LMMSE 40 3.4.1 Optimization Criterion 41 3.5 Postcombining LMMSE 46 3.6 Modified LMMSE Algorithm 50 Chapter 4 Computer Simulation 53 4.1 Simulation Parameters 53 4.2 Simulation of Postcombining LMMSE Receiver 54 4.3 Simulation of Modified LMMSE Receiver 56 4.3.1 Simulation in the Single User Environment 56 4.3.2 Simulation in the Multiuser Environment 58 4.4 Comparison Between the Conventional, Postcombining LMMSE, and Modified LMMSE receiver 61 4.5 Simulation of the System Imperfection on Modified LMMSE Receiver 63 4.5.1 Simulation of MSE = 0.01 63 4.5.2 Simulation of MSE = 0.2 66 4.6 Simulation of the Vehicle Speed on Modified LMMSE Receiver 68 Chapter 5 Conclusion 75 Bibliography 77