在直接序列分碼多工(DS-CDMA)系統，因為展頻碼非完全正交(Orthogonal)，所產生的多用戶之間干擾(Multiple access interference ; MAI)導致系統容量受到限制。而在無線傳輸過程中，因多重路徑所產生的符號間干擾效應(Inter-symbol interference ; ISI)，會使得系統效能降低。為了解決上述問題，許多適應性多用戶偵測器被提出，較常見的有利用最小均方誤差(Minimum mean square error ; MMSE) 法則來設計接收機。但MMSE接收機必須需要訓練序列(Training sequence)，而使用訓練序列將會降低頻寬效益(Spectral efficiency)。為了提升頻寬效益我們可以採用不需要訓練序列之盲蔽式接收機 (Blind receiver)。傳統盲蔽式接收機之設計是採用限制性最小變異數(Linear constrained minimum variance ; LCMV)法則， 文獻上已經多種盲蔽式接收機被陸繼提出。 基本上 LCMV法則可以被視為是最小輸出能量(Minimum output energy; MOE)法則的限制性版本(Constrained version)。 此外，還有許多利用常模(Constant modulus; CM)法則所設計的線性限制性常模(Linear constrained constant modulus ; LCCM)接收機。 根據文獻報告採用線性限制性常模之接收機較使用限制性最小變異數接收機，對系統參數之改變具有強韌性(Robustness)。

傳統上我們可以使用上述方法來抑制符號間干擾及多用戶干擾，為了能適應不同系統環境， 利用傳統適應性多用戶接收機所得到之系統效能無法滿足我們的需求。 為了進一步提升系統效能，在本論文中我們擬提出具前置編碼 (Pre-code)之新適應性DS-CDMA系統接收機。 利用前置編碼的特性我們可以將消除符號間干擾，再利用適應性偵測器抑制多用戶干擾。 相對的我們必須損失一些頻寬效益以換取系統效能。 做法上， 前置編碼之處理與傳統正交分頻多工技術(OFDM)中所使用之循環前置碼(Cyclic prefix ; CP)或者補零冗餘符碼(Zero padded ; ZP)當作前置編碼(Pre-coding) 非常相似。 在本論文中我們利用循環前置碼或者補零冗餘符碼方式，將其應用在DS-CDMA系統可以有效消除符碼間干擾(ISI)。 之後也可以搭配傳統之適應性接收機， 使得所估測之通道參數更為精確，降低錯誤率，提升系統效能。

The system capacity of the direct-sequence code division multiple access (DS-CDMA) system is limited mainly due to the multiple access interference (MAI), this is basically due to the incomplete orthogonality of spreading codes between different users. In wireless communication environments, the use of DS-CDMA system over multipath channels will introduce the effect of inter-symbol interference (ISI), thus the system performance might degrade, dramatically. To circumvent the above-mentioned problems many adaptive multiuser detectors are proposed, such as the minimum mean square error (MMSE) criteria subject to certain constraints. Unfortunately, with the MMSE receiver it requires an extra training sequence, which decreases the spectral efficiency. To increase the spectral efficiency, the blind adaptive receivers are adopted. In the conventional approach the blind adaptive receiver is developed based on the linear constrained minimum variance (LCMV) criteria, which can be viewed as the constrained version of the minimum output energy (MOE) criteria. Other alternative of designing the blind adaptive receiver is to use the linear constrained constant modulus (LCCM) criteria. In general, the LCCM receiver could achieve better robustness due to the changing environment of channel.
With the above-mentioned adaptive linearly constrained multi-user receivers, we are able to reduce the effects of ISI and MAI and achieve desired system performance. However, for worse communication link, the conventional adaptive multi-user detector might not achieve desired performance and suppress interference effectively. In this thesis, we consider a new approach, in which the pre-coder similar to the Orthogonal Frequency Division Multiplexing (OFDM) systems is introduced in the transmitter of the DS-CDMA system. In the receiver, by using the characteristics of pre-coder we could remove the effect of ISI, effectively, and follows by the adaptive multi-user detector to suppress the MAI. Two most common use pre-coders of the OFDM systems are the Cyclic Prefix (CP) or Zero Padding (ZP). Thus the pre-coded DS-CDMA systems associated with the adaptive blind linearly constrained receiver could be employed to further improve the system performance with the cost of decreasing the spectral efficiency.

中文摘要 i
英文摘要 ii
目錄 iii
圖表目錄 vi

第一章
簡介 1

第二章
傳統直接序列分碼多工系統之適應性接收機介紹 4
2.1 概論 4
2.2 離散時間直接序列分碼多工系統模型 5
2.3 廣義旁波帶消除器之遞迴式最小平方值演算法 10
2.4 線性限制性常模法則之遞迴式最小平方值演算法 14
2.5 廣義旁波帶限制性常模法則之遞迴式最小平方值演算法 17

第三章
前置編碼單輸入多輸出分碼多工系統 21
3.1 概論 21
3.2 前置編碼分碼多工系統模型 22
3.2.1循環前置碼 22
3.2.2補零冗餘符碼 28

3.3 循環前置碼之單輸入多輸出分碼多工系統 31
3.3.1 耙式接收器 31

第四章
模擬結果 39
4.1 模擬結果 39
4.2 系統效能分析與比較 47

第五章
結論 50
5.1 結論 50

參考文獻 51

附錄A 53

附錄B 55

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