近年來，基於各種新發展之無線通訊服務以及設備，人們對於無線通訊的需求日漸增加。同時，我們期望未來之無線通訊系統能提供高品質與高速率之服務。為了達到以上的需求，具有多輸入多輸出 (Multiple-input multiple-output; MIMO) 天線的時間－空間區塊編碼 (Space-time block code; ST-BC) 之分碼多工 (Code division multiple access; CDMA) 系統，是目前為大家所採用的一種可行方案。在此系統中，使用多個傳送或接收天線所產生的空間多樣性 (Spatial diversity) 以及時間－空間區塊編碼，是我們可以有效改善系統傳輸品質的主要關鍵。許多針對時間－空間區塊編碼之分碼多工系統設計的多用戶接收技術已經陸續被提出。其中，在參考文獻 [8]，作者提出了所謂的盲蔽式卡彭接收機 (Blind Capon receiver)，其架構為一個兩分支的濾波器組 (Filterbank) 及盲蔽式的卡彭通道估測器。盲蔽式卡彭接收機之設計，基本上是採用線性限制條件最小變異數 (Linearly constrained minimum variance; LCMV) 法則。然而，此法則對於不匹配 (Mismatch) 效應相當敏感。這裡所謂的不匹配效應指的是針對主要用戶 (Desired user) 做同步時所產生之時間誤差 (Timing error)。換句話說，根據線性限制條件最小變異數法則所設計的接收機在不匹配效應的影響之下將無法有效運作，且系統品質將嚴重下降。

在本論文中，我們提出一個新的盲蔽式適應性多輸入多輸出分碼多工接收機。其中，我們採用線性限制條件常模 (Linearly constrained constant modulus; LCCM) 法則設計此接收機的濾波器組，主要的動機是考慮到常模法則對於不匹配效應較不敏感。另外，為了減少接收機的複雜度，我們採用廣義旁波帶消除器 (Generalized sidelobe canceller; GSC) 之架構配合遞迴式最小平方值 (Recursive least squares; RLS) 演算法，來實現我們所提出的適應性線性限制條件常模多輸入多輸出分碼多工濾波器組。在GSC之架構下，我們擬推導出所謂的MIMO CM-GSC-RLS演算法。為了與我們的所設計之方法做比較，我們也推導了一個以文獻 [8] 為主之適應性盲蔽式卡彭接收機，稱之為適應性MIMO MV-GSC-RLS演算法。另一方面，文獻 [8] 之中所採用的信號模型假設通道特性為頻率平坦 (Frequency-flat)。為了得到一個更實際的信號模型，我們將會將該信號模型做延伸，也就是把多重路徑 (Multipath) 通道納入考慮。在此延伸之中，我們將針對時間－空間區塊編碼的特殊架構所造成之符碼間干擾 (Inter-symbol interference; ISI) 做特別的探討。最後，我們將會完整的討論存在於多重路徑信號模型中的一些問題，包含截短 (Truncate) 接收信號之必要性以及如何在時變通道的情況下修正我們的模型。

In recent years, demands on all kinds of wireless communications become heavier due to the developments of new services and devices. At the same time, future wireless networks are expected to provide services with high quality and data rate. A possible solution which can attain these objectives is wireless communication systems that use multiple-input multiple-output (MIMO) antennas along with Alamouti’s space-time block code and direct-sequence code division multiple access (DS-CDMA) modulation technique. In such systems, spatial diversity rendered by multiple antennas as well as coding in spatial and time domains are the keys to improve quality of transmission. Many multiuser detection techniques for the space-time block coded CDMA systems have been investigated. In [8], the blind Capon receiver was proposed, which consists of a two-branch filterbank followed by the blind Capon channel estimator. The design of blind Capon receiver is based on linearly constrained minimum variance (LCMV) criterion, which is known to be sensitive to inaccuracies in the acquisition or tracking of the desired user's timing, referred to as mismatch effect. In other words, the LCMV-based receiver may perform undesirably under mismatch effect.

In this thesis, we propose a new blind adaptive MIMO-CDMA receiver based on the linearly constrained constant modulus (LCCM) criterion. This work is motivated by the robustness of LCCM approach to the mismatch effect. To reduce the complexity of receiver design, framework of the generalized sidelobe canceller (GSC) associated with the recursive least squares (RLS) algorithm is adopted for implementing the adaptive LCCM MIMO-CDMA filterbank. Based on the GSC-RLS structure, we derive the proposed MIMO CM-GSC-RLS algorithm. For the purpose of comparison, an adaptive implementation of the blind Capon receiver proposed in [8] is also derived, which is referred to as the MIMO MV-GSC-RLS algorithm. We note that the signal model in [8] was constructed under assumption of frequency-flat channels. To obtain a more practical and realistic signal model, in this thesis we extend the system and channel model by including multipath effects in the beginning of our work. In completing this extension, inter-symbol interference (ISI) caused by the special coding scheme of ST-BC will be specifically analyzed. Finally, a full discussion of the multipath signal model will be provided, including necessity of truncating the received signals as well as modifications in the signal model when considering time-varying channels.

Via computer simulations, advantages of the proposed scheme will be verified. Compared to the conventional blind Capon receiver, we will show that the performance of the proposed CM-GSC-RLS algorithm is better. This is especially true when mismatch problem is considered in the MIMO-CDMA systems of interest. The proposed scheme show more robustness against the mismatch effects than the conventional blind Capon receiver. Moreover, the benefit resulted by truncating the received signals is also demonstrated, especially for binary phase-shift-keying (BPSK) modulated source symbol. Finally, simulations considering time-varying channels are provided to reveal that our proposed scheme can adapt itself to the time-varying environments appropriately.

Acknowledgements i
Abstract ii
Contents iv
List of Figures vi
List of Tables viii
Chapter 1 Introduction 1
Chapter 2 Conventional Blind Capon Receiver for Space-Time Block Coded CDMA Systems in Frequency-Flat Channels 6
2.1 Introduction 6
2.2 Space-Time Block Code (ST-BC) 7
2.3 Downlink MIMO-CDMA Systems with ST-BC in Frequency-Flat Channels 11
2.4 MMSE Receiver and Blind Capon Receiver 15
Chapter 3 Blind Adaptive MIMO-CDMA Receiver with MIMO CM-GSC-RLS Algorithm in Multipath Channels 19
3.1 Introduction 19
3.2 Downlink MIMO-CDMA Systems with ST-BC in Multipath Channels 20
3.3 Blind Adaptive MIMO CM-GSC-RLS Algorithm 29
3.4 Truncation of Received Signals 37
3.5 Signal Model in Time-Varying Channels 42
Chapter 4 Simulation Results 47
4.1 Preliminaries 47
4.2 Simulation Results 49
Chapter 5 Conclusions and Future Work 64
5.1 Conclusions 64
5.2 Future Work 65
Appendix A Method of Selecting in MIMO CM-GSC-RLS Algorithm 67
Appendix B Adaptive Implementation of Blind Capon Receiver 69
Appendix C Iterative Subspace-Based Channel Estimation 73
References 77

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