臺灣博碩士論文加值系統

在寬頻無線傳輸的環境中，正交分頻多工技術（Orthogonal Frequency Division Multiplexing, OFDM）被提出來用以應付無線傳輸通道中的多路徑衰減（multi-path fading）的問題，因為在OFDM系統裡能將頻率選擇性衰減（frequency selective fading）通道細分為數個子通道以使其變成平坦衰減（flat fading），這樣子只要在每個子通道輸出上加上一個簡單的頻域等化器（frequency domain equalizer）如此即可將衰減的信號補償回來。但是相對的OFDM系統對於頻率飄移（frequency offset）的抵抗能力則非常低落，產生頻率飄移的原因最常見的為傳送端與接收端的震盪器的頻率不相同，或是傳送端與接收端間的相對運動所造成的都卜勒效應。一旦每個子通道的正交特性不成立，則這些子通道將會彼此互相干擾，對於系統效能的影響十分巨大，因此如何將傳送端與接收端的載波頻率調整一致與如何調整系統時間的同步（synchronization），則是一個相當重要的課題。
在本文中，將提出一個簡單、迅速且準確性高的同步技術，並透過數學理論基礎與程式模擬來驗證此技術的特性與效能及可靠度，最後經由整個系統的特性響應來分析與討論這個同步技術的優缺點。

A high spectral efficient transmission scheme called Orthogonal Frequency Division Multiplexing (OFDM) has been presented for wireless communication recently which is useful to combat the errors caused by multi-path fading channel. In fact, OFDM provided a good protection against the effects of serve multi-path propagation, cochannel interference and impulsive parasitic noise. However this technique is very sensitive to the frequency offset between the transmitter and receiver oscillators. In the presence of a carrier frequency error, the subcarriers making up the OFDM signal loose their orthogonality and the system performance becomes degraded. The main work of this thesis is to propose a new carrier frequency synchronization and timing recovery algorithm in OFDM system.
In this paper, a simple, fast and extremely accurate carrier frequency synchronization method is proposed. Mathematics derivation of this method is introduced. Furthermore, the technique is simulated and analyzed by computer. Finally, we discuss the system performance and make some conclusions.

目 錄
中文摘要 i
英文摘要 ii
誌謝 iii
目錄 iv
圖目錄 vii
表目錄 xi
第一章 前言
第二章 寬頻正交分頻多工系統簡介
2-1 簡介
2-2 基本概念
2-3 OFDM調變原理
2-4 寬頻正交分頻多工系統的問題
2-5 MATLAB模擬模型
2-6 總結
第三章 Mobile Radio Propagation Channel Model
3-1 傳輸通道簡介
3-2 大範圍衰減模型
3-3 小範圍衰減模型
3-3.1 從時域上觀察訊號在時間上的散亂現象
3-3.2 從頻域上觀察訊號在時間上的散亂現象
3-3.3 從時域上觀察通道在時間上的變動行為
3-3.4 從頻域上觀察通道在時間上的變動行為
3-4 通道模型的系統函數
3-4.1輸入延遲擴散函數(Input delay spread function)
3-4.2輸出都卜勒擴散函數(Output Doppler spread function)
3-4.3時變轉移函數(Time variant transfer function)
3-4.4延遲都卜勒擴散函數(Delay Doppler-spread function)
3-5 WSS通道模型
3-6 US通道模型
3-7 WSSUS通道模型
3-8 Jakes 衰減通道模型
3-9 COST 207 通道模型
3-10 提出的通道模擬模型
第四章 WOFDM系統同步技術原理與特性分析
4-1 簡介
4-2 載波同步技術介紹
4-2.1整數倍的頻率偏移對系統的影響
4-2.2小數部分的頻率偏移對系統的影響
4-3 符元同步(框碼同步)
4-4 取樣頻率錯誤與通道預估
4-5 總結
第五章GPD(Guardband Power Detection)載波頻率同步技術的分析與模擬
5-1 GPD載波頻率同步技術簡介
5-2 GPD方法理論與模擬模型方法
5-2.1 GPD方法一介紹
5-2.2 GPD方法二介紹
5-2.3 GPD方法三介紹
5-2.4 GPD方法四介紹
5-3 Maximum Likelihood Estimate(MLE)方法介紹
5-4 各種方法模擬結果
5-4.1 GPD方法一的模擬結果
5-4.2 GPD方法二的模擬結果
5-4.3 GPD方法三的模擬結果
5-4.4 GPD方法四的模擬結果
5-4.5 MLE方法的模擬結果
5-5 模擬結果的比較與分析
5-6 總結
第六章 結論
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