本論文主要在探討如何對分碼多工系統接收端之同步碼追蹤迴路(code tracking loop)之效能進行改善。對於CDMA的系統而言，展頻碼的使用及選取是非常重要的技術，將會影響展頻通訊之效能。在接收端，亦是利用了展頻碼的自相關特性來作解展頻。若接收端與傳送端之展頻碼間的時間差超過一個子碼時間，相關器所得之訊號功率將變小而不利於解調。但因為無線的通道相當的複雜且易變，所以如何找出精確的傳送延遲，對接收機便是相當重要的技術。
本論文以1980年提出的改進式碼追蹤迴路(MCTL)為基礎，並結合了解相關直接回授偵測器(decorrelator decision feedback detector, DDFD)以及簡化式多路徑干擾消除器(MPI cancellator)兩架構，來改進傳統碼追蹤迴路之效能。解相關直接回授偵測器為多用戶偵測器，用以降低多用戶之干擾。而多路徑干擾消除器是利用相關器及濾波器等，來有效降低多重路徑干擾之影響。
論文中對此偽雜訊展頻碼追蹤迴路作詳細介紹以及程式的分析比較。主要是對追蹤迴路之特徵鑑別器(S-curve)、均方追蹤誤差(mean-square tracking jitter)以及平均脫離鎖定時間(mean time to loss lock, MTLL)等分析，並與傳統的追蹤迴路作比較。由論文中分析可發現：在不考慮硬體複雜度的前提下，相較於傳統的展頻碼追蹤迴路，論文中整合之架構能有效降低多路徑干擾及多用戶干擾對追蹤迴路之影響，而獲得更佳的效能。

A non-coherent PN code tracking loop with multi-user detection and simplified multi-path interference cancellation (MPIC) is proposed for direct sequence spread spectrum communications system. A decorrelator decision-feedback detector (DDFD) is first applied on the incoming signal to mitigate the multi-user interference. Then, a simplified multi-path interference cancellation (MPIC) is further used to increase signal quality. Finally, a modified code tracking loop (MCTL) is adopted for non-coherent PN code tracking. Mathematical expressions of the S-curve and tracking jitter are derived. Mean time to lose lock is also compared with traditional tracking loops.
From the numerical results, we know the proposed PN code tracking loop can efficiently mitigate the interference from multi-user and multi-path and improve the performance of code tracking loop.

目錄 …………………………………………………………………………………I
圖表目錄 ………………………………………………………………………….III
第一章 緒言 ………………………………………………………………………1
1.1 研究動機 …………………………………………………………………1
1.2 論文架構 …………………………………………………………………3
第二章 傳統PN碼追蹤迴路之介紹與分析 ………………………….4
2.1 傳統之最佳追蹤迴路 …………………………………………………5
2.2 延遲鎖定追蹤迴路(DLL)之分析 ………………………………………7
2.2.1 同調之延遲鎖定追蹤迴路(coherent DLL)介紹 …………………7
2.2.2 非同調之延遲鎖定追蹤迴路(non-coherent DLL)介紹 …………17
2.3 Tau-dither追蹤迴路 ……………………………………………………20
2.4 改進式碼追蹤迴路(Modified Code Tracking Loop, MCTL) …………22
第三章 多用戶干擾與多路徑干擾對傳統DLL之影響 ………………35
3.1 受干擾下的DLL之系統分析 …………………………………………35
3.2 模擬分析圖 ……………………………………………………………41
第四章 具多路徑干擾消除及多用戶檢測之改進式PN碼追蹤迴路…46
4.1 多用戶檢測器之介紹 …………………………………………………46
4.1.1 解相關偵測器(Decorrelator detector) ……………………………47
4.1.2 解相關廻授判斷偵測器(Decorrelator Decision Feedback Detector, DDFD) ……………………………………………………………49
4.1.3 多用戶偵測器之效能分析 ………………………………………50
4.2 多路徑干擾消除器 ……………………………………………………51
4.3 具多路徑干擾消除及多用戶檢測之改進式PN碼追蹤迴路 ………57
4.3.1 追蹤迴路系統之介紹與分析 ……………………………………58
4.3.2 迴路分析模擬圖 …………………………………………………71
第五章 建議與結論 …………………………………………………………78
附錄A. 特徵鑑別器之分析……………………………………………79
附錄B. 干擾項之功率譜密度計算…………………………………81
參考文獻 …………………………………………………………………83

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