直接序列分碼多工(DS-CDMA)技術為目前無線通訊系統中多重同時傳輸所採用的重要技術之一。而本論文目的是提出一個新的線性限制性常模之修正型共軛梯度(LCCM-MCG)適應性濾波器演算法，來抑制在直接序列分碼多工系統，以及多重路徑衰落通道環境下之多用戶接取干擾(MAI)，並處理因通道係數估測不準確所造成通道不匹配(channel mismatch)的問題。事實證明，以共模準則之適應性濾波器演算法的確能有效降低因不完美通道係數估測所造成的影響。在本論文中所推導出線性限制性常模之修正型共軛梯度演算法，係根據廣義旁波帶消除器(GSC)架構推得，而此種方法具有較好的穩定性，且比一般的最小平方和演算法(RLS)的計算複雜度低，除此之外，其可用於多用戶之耙式(RAKE)接收器中，達到不錯的效果。而這種修正型共軛梯度演算法(MCG)對於每個時間取樣的輸入資料，其權重更新只需要一次遞回疊代，且具有與最小平方和演算法差不多的效能表現。由電腦模擬的結果顯示，可以驗證我們提出的線性限制性常模之修正型共軛梯度演算法具有快速收斂特性，且能夠有效克服通道估測不匹配所造成的效應。當電腦模擬以位元錯誤率(BER)為效能表現指標時，我們可以發現線性限制性常模之修正型共軛梯度演算法的表現與線性限制性常模之最小平方和演算法(LCCM-RLS)[18]幾乎一樣，且其優於以最小輸出功率(MOE)準則導出之統計性梯度下降(SGD)演算法[7]。

The direct-sequence code division multiple access (DS-CDMA) is one of the significant techniques for wireless communication systems with multiple simultaneous transmissions. The main concern of this thesis is to propose a new linearly constrained constant modulus modified conjugate gradient (LCCM-MCG) adaptive filtering algorithm to deal with problem of channel mismatch associated with the multiple access interference (MAI) in DS-CDMA system over multipath fading channel. In fact, the adaptive filtering algorithm based on the CM criterion is known to be very attractive for the case when the channel parameters are not estimated perfectly. The proposed LCCM-MCG algorithm is derived based on the so-called generalized sidelobe canceller (GSC). It has the advantage of having better stability and less computational complexity compared with conventional recursive least-squares (RLS) algorithm, and can be used to achieve desired performance for multiuser RAKE receiver. Moreover, with the MCG algorithm it requires only one recursive iteration per incoming sample data for updating the weight vector, but still maintains performance comparable to the RLS algorithm. From computer simulation results, we show that the proposed LCCM-MCG algorithm has fast convergence rate and could be used to circumvent the effect due to channel mismatch. Also, the performance, in terms of bit error rate (BER), is quite close to the LCCM-RLS algorithm suggested in [18], and is superior to the stochastic gradient descent (SGD) algorithm proposed in [7].

Acknowledgement…………………………………………i
Abstract…………………………………………………ii
Contents…………………………………………………iii
List of Figures and Tables……………………………………………………v
Chapter 1 Introduction…………………………………………………………1
Chapter 2 Conventional Multiuser Detectors for DS-CDMA System over Multipath Fading Channel
2.1 Introduction………………………………………………………………5
2.2 Overview of DS-CDMA System and Problem Description……………7
2.3 System Model Description……………………………………………10
2.4 RAKE Diversity and Multiuser Detectors with Adaptive Algorithms Based on Minimum Output Energy (MOE) Criterion…………………14
2.4.1 RAKE Diversity………………………………………………15
2.4.2 Stochastic Gradient Descent Algorithm Based on Minimum Output Energy Criterion………………………………………16
2.4.3 Linear Constrained Recursive Least-Squares Algorithm……17
2.4.4 Linear Constrained Modified Conjugate Gradient Algorithm…19
Chapter 3 Adaptive Multiuser Detector with LC Constant Modulus Modified Conjugate Gradient Algorithm
3.1 Introduction……………………………………………………………23
3.2 Linear Constrained Constant Modulus Recursive Least-Squares Algorithm………………………………………………………………24
3.3 Linear Constrained Constant Modulus Modified Conjugate Gradient Algorithm………………………………………………………………26
3.4 Computer Simulation Results…………………………………………33
Chapter 4 Conclusions……………………………………………………………42
Appendix A……………………………………………………………44
Appendix B……………………………………………………………46
References………………………………………………47

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