李學智臺灣大學：電信工程學研究所胡文峰Hu, Wen-FengWen-FengHu2007-11-272018-07-052007-11-272018-07-052005http://ntur.lib.ntu.edu.tw//handle/246246/58585在本篇論文中，對於一個多用戶分碼多工 (CDMA)超寬頻(UWB)系統，我們採用多用戶偵測器與多天線技術去改善系統的效能。然後，藉由程式的模擬來比較多用戶偵測器與多天線技術的效能改善。在無線通訊中，通道的延遲擴散會產生符號間的互相干擾(ISI)，因此，在本篇論文中我們藉由等化器與通道偵測器去補償ISI。除此之外，我們把時間分集的概念應用到接收器架構上，結合多路徑抵達接收器的能量，可以有效地提高訊雜比值。使用耙式接收器是一可行的方法。 由於用戶間的展頻碼有低相關的特性，藉由這個特性可以推導出一組線性轉換去分離各用戶的訊號。若用戶的展頻碼為未知，這時候就必須使用盲蔽(blind) 和適應性(adaptive)的多用戶偵測技術。這種多用戶偵測技術可以降低複雜度以及追蹤快速變化的環境。 本文另一個討論的主題是多天線的系統，這個系統依在傳送端與接收端的天線數目可分為：一對多(SIMO)、多對一(MISO)、與多對多(MIMO)三大類別。在一對多和多對一的系統上，空間和時間上分集效應的結合(diversity combing)可以提升系統效能。 另一方面，在實際通訊系統中，天線扮演了非常重要的角色，它對於系統的表現有一定的影響。本文的最後對於天線做了一些的討論，比較天線效應對於分碼多工超寬頻系統與正交分頻多工(OFDM)超寬頻系統的效能影響。In this thesis, we adopt Multi-User Detection (MUD) and multi-antenna technique in a DS-CDMA UWB system. Then, based on the simulation results, we compare the improvement in system performance between MUD and multi-antenna technique. During wireless communication, the channel delay spread will cause considerable Inter Symbol Interference (ISI) and hence equalizer or channel estimator has to be employed. Besides, we can utilize multipath energy to increase Signal to Noise Ratio (SNR). The use of a RAKE receiver is one possible method. Due to the lower correlation of users’ spreading code, we apply them to obtain the weightings of the typical MUD receiver. If the receiver doesn’t know all users’ spreading code, blind adaptive MUD receiver is applied, which has the lower complexity and can track the fast-varying channel. The multi-antenna technique can be classified into SIMO、MISO and MIMO systems. The spatial and time diversity combining techniques are employed to improve the system performance in SIMO and MISO systems. On the other hand, the antenna effect is crucial in the UWB system. Therefore, we compare the antenna effect between the DS-CDMA UWB system and MB-OFDM UWB system.Ⅲ Contents Abstract Ⅰ Contents Ⅲ List of Figures Ⅶ List of Tables XI Chapter 1 Introduction............................................................................................ 1 1.1 Development of UWB ................................................................................... 1 1.2 Concepts of Multi-user Detection ................................................................ 2 1.3 Concepts of Multi-Antenna.......................................................................... 3 1.4 Motivation and Organization of this Thesis ............................................... 3 Chapter 2 Background ............................................................................................ 7 2.1 What is UWB................................................................................................. 7 2.1.1 Pulse Shaping.......................................................................................7 2.1.2 Reference Spectral Mask ................................................................... 10 2.2 Characteristics of UWB...............................................................................11 2.3 Spread Spectrum Techniques..................................................................... 12 2.3.1 Spreading Sequences .........................................................................13 2.3.2 Concepts of Direct Sequence Spread Spectrum................................. 13 Chapter 3 System Architecture............................................................................. 17 3.1 Transmitter Structure................................................................................. 17 Contents IV 3.2 Modified Saleh-Valenzuela Model............................................................. 19 3.2.1 Channel Model 1................................................................................ 23 3.2.2 Channel Model 2................................................................................ 24 3.2.3 Channel Model 3................................................................................ 24 3.2.4 Channel Model 4................................................................................ 25 3.3 Receiver Structure....................................................................................... 26 3.3.1 RAKE Receiver .................................................................................27 3.3.2 Linear Equalizer.................................................................................28 3.3.3 Linear Square Error Channel Estimator............................................. 32 Chapter 4 Multi-user Detection and Multi-Antenna Technique ....................... 37 4.1 MUD Techniques in a UWB System.......................................................... 37 4.1.1 Typical MUD .....................................................................................38 4.1.1.1 Decorrelating Detector............................................................ 39 4.1.1.2 Linear Minimum Mean Square Error Detector....................... 40 4.1.2 Blind Adaptive MUD......................................................................... 42 4.1.2.1 Minimum Output Energy-LMS Detector................................ 44 4.1.2.2 Minimum Output Energy-RLS Detector................................. 45 4.2 Multi-Antenna Technique in a UWB System ........................................... 46 4.2.1 SIMO System..................................................................................... 46 4.2.2 MISO System..................................................................................... 48 4.3 Simulation Results ...................................................................................... 50 4.3.1 Performance of the AWGN channel................................................... 52 4.3.2 Performance of the Statistical channel............................................... 53 4.3.2.1 Performance of CM 1..............................................................53 4.3.2.2 Performance of CM 2..............................................................55 Contents V 4.3.2.3 Performance of CM 3..............................................................56 4.3.2.4 Performance of CM 4..............................................................58 4.3.2.5 Comparison between MUD and Multi-Antenna Technique ... 59 Chapter 5 UWB Antenna Effect of DS-CDMA and MB-OFDM....................... 63 5.1 Antenna Effect of Pulsed UWB.................................................................. 63 5.2 Antenna Effect on MB-OFDM UWB ........................................................ 65 5.2.1 MB-OFDM System Architecture..................................................... 65 5.2.2 Antenna Effect.................................................................................. 66 5.3 Antenna Effect between DS-CDMA UWB and MB-OFDM UWB ....... 68 Chapter 6 Conclusion ............................................................................................ 73 References.................................................................................................................. 77 Contents VI5663622 bytesapplication/pdfen-US超寬頻直接序列分碼多工耙式接收器線性等化器線性通道偵測器時間分集路徑分集最小平均誤差平方法多用戶偵測可適性猜測技術子空間追蹤最小輸出能量法多天線系統多輸入多輸出最大比例結合空時編碼正交分頻多工Ultra-Wideband (UWB)Direct-Sequence Code-Division Multiple Access (DS-CDMA)RAKE receiverLinear Equalizer (LE)Linear channel estimatortime diversitypath diversityMinimum Mean-Square Error (MMSE)Multi-use Detection (MUD)blind adaptive techniquesubspace trackingMinimum Output Energy (MOE)multi-antennaMIMOMaximum Ratio Combining (MRC)Space Time Block Code (STBC)Orthogonal Frequency Division Multiplexing (OFDM)thesishttp://ntur.lib.ntu.edu.tw/bitstream/246246/58585/1/ntu-94-R92942073-1.pdf