Linear Multiuser Detection for Asynchronous DS-CDMA UWB in the Indoor Environments

針對超寬頻脈波直序展頻多工存取系統，我們說明了可適性最小均方誤差多用戶接收器可以有效地收集由多路徑而來的能量而消減多重存取及符際間和位元間的干擾如同參考文獻[10]所言。因為超寬頻系統的路徑解析度相當細微，而使通道分解成相當高程度的多路徑是此系統的最主要的問題所在，也是我們在此論文中探討的重點。在可控制的複雜度之下，可適性地實現最小均方誤差多用戶接收器被我們證實出有能力在表現上提供可預期增益。再者，我們提出非同調最小均方誤差接收器如果通道的相位是隨時間而變化。我們證實用來調整濾波器係數的非同調可適性演算法在相位變化的環境下仍可以收斂到所欲求的結果，反之，傳統的可適性演算法卻發散掉。最後，我們提出可適性濾波器組當作M維二相正交鍵直序展頻分碼多工系統的多用戶接收器。我們也算出理想上最小均方誤差接收器的表現，其中也包括了二維二相正交鍵，也就是一開始我們提到的架構。我們證實此可適性接收器相對於理想情況下付出幾dB的損失。而理想上的最小均方誤差接收器也大概比AWGN通道下的情況少6dB。所以，在此考慮的接收器架構是可以抗近-遠效應的We demonstrate that the adaptive MMSE multiuser receiver can effectively gather multipath energy and eliminate the multiple-access, intersymbol and interchip interference for an ultra-wideband (UWB) pulse based direct sequence spread spectrum system using code division multiple access following on the early work [10]. A high level of multipath fragmentation caused by the fine path resolution of wideband (3.1-5.15 GHz) channel is the dominant problem, which we treat in this thesis. We prove that the adaptive implementation of MMSE receiver has the potential of providing the anticipated performance gains with a complexity that would be manageable. Also, we propose a noncoherent MMSE receiver if the channel phase is time-variant. We show that the noncoherent adaptive algorithms for filter adjustment can converge in the presence of phase variations, whereas their conventional counterparts diverge. Finally, we propose adaptive filter banks as the multiuser receiver for MBOK DS-CDMA UWB systems. We also compute the analytic performance of ideal MMSE for MBOK system from the idea of its special case, 2-BOK. The adaptive MMSE receiver shows only an additional decibel of loss over the ideal version. And the ideal MMSE receiver also showed only a 6-dB penalty versus the AWGN channel case. Hence, the regarded linear MBOK adaptive multiuser receiver is near-far resistant.Contents i List of Figures vi Chapter 1 Introduction 1 1.1 Ultra-wideband (UWB) Technology 1 1.2 Introduction of Multiuser Detection 2 1.3 Overview of this Thesis 3 Chapter 2 Background 5 2.1 System Model for Synchronous DS-CDMA System 5 2.2 Optimal Multiuser Receiver 10 2.3 Linear Multiuser Detector 11 2.3.1 Conventional Matched Filter Bank 13 2.3.2 Decorrelating Detector 13 2.3.3 Minimum Mean-Square-Error Detector 14 2.4 M-ary Bi-orthogonal Keying (MBOK) 15 2.4.1 Transmitter Structure 15 2.4.2 Conventional Receiver 16 2.5 Channel Model for Ultra-Wideband (UWB) in the Indoor Environment 17 Chapter 3 Linear Multiuser Detector for Asynchronous DS-CDMA UWB System 20 3.1 General System Model for Asynchronous DS-CDMA UWB System 20 3.2 RAKE Receiver 22 3.2.1 One-finger (Matched Filter) 25 3.2.2 Infinite-finger RAKE Receiver (Ideal RAKE Receiver) 25 3.2.3 Main-finger RAKE Receiver 25 3.3 Linear Adaptive Multiuser Detector 26 3.3.1 Receiver Structure 26 3.3.2 Adaptive Algorithms 30 3.4 Noncoherent Linear Adaptive Multiuser Detector 31 3.4.1 System Model 31 3.4.2 Receiver Structure 33 3.4.3 Adaptive Algorithms 35 3.5 Performance Analysis 36 3.5.1 Performance of MMSE Receiver 36 3.5.2 Signal-to-Interference Ratio (SIR) Convergence Comparison 42 Chapter 4 MBOK Linear Multiuser Detector 44 4.1 System Model 44 4.2 Receiver Structure 46 4.3 Adaptive Algorithm 48 4.4 Performance Analysis 51 4.4.1 Performance of MMSE Receiver 51 4.4.2 Signal-to-Interference Ratio (SIR) Convergence Comparison 55 Chapter 5 Simulation Results 57 5.1 System Description 57 5.1.1 System Parameters 58 5.2 Simulation Results 62 5.2.1 UWB Channel Model 62 5.2.2 Performance of the Linear Adaptive MMSE Multiuser Detector 64 5.2.3 Performance of the Noncoherent Linear Adaptive MMSE Multiuser Detector 70 5.2.4 Performance of the 4BOK System 74 Chapter 6 Conclusions 79 References 8