在正交分頻多工系統中，當傳送信號區塊經過具多重路徑干擾的通道後，由於通道延遲擴散效應的影響，目前時刻的傳送信號區塊將遭受上一時刻傳送信號區塊的干擾，為了處理這個問題，傳統上我們會在傳送信號區塊與區塊之間加入一段保護區間，避免區塊間的干擾，保護區間的加入方式最常見的有補零冗餘符碼與循環前置碼兩種，其中，補零冗餘符碼的做法是在正交分頻多工系統的傳送信號區塊後端加入保護區間，保護區間中填入零，其長度必須大於或等於通道長度，由此便可以避免區塊間干擾的問題，但具多重路徑干擾通道也會使得子載波之間正交性喪失，造成載波間干擾的問題，而保護區間使用循環前置碼方式則可以處理這個問題，其作法為複製經過正交分頻調變後傳送信號區塊的尾端長度四分之一，置於傳送區塊前，一方面避免區塊間干擾的問題，同時達到保持子載波之間的正交性。
不論上述任一種方法，都將使得資料的傳送速率下降，造成通訊資源的浪費，因此在本論文中，我們將不同於傳統作法在正交分頻多工系統的傳送信號區塊加入保護區間，而是讓傳送信號區塊直接進入具多重路徑干擾的通道中，在接收端所收到的接收信號中存在著區塊間干擾與載波間干擾的問題，文中將提出一非正交投影器負責處理區塊間干擾的問題，並且結合廣義旁波帶消除等化器[1]，抑制載波間干擾並且解調接收信號。
利用電腦模擬非時變通道環境及時變通道環境下，使用非正交投影配合廣義旁波帶消除等化器架構，由結果中可知，本論文提出的非正交投影器確實可以達到消除未加入保護區間之正交分頻多工系統接收信號中的區塊間干擾，並且在延遲擴散效應較嚴重時，相對地達到較好的結果。

In orthogonal frequency division multiplexing (OFDM) systems, when transmitted blocks of signal through the multipath channel, the present transmitted blocks of signal will be interfered by the previous one due to the effect of channel delay spread. In order to solve this problem, conventionally we introduce a guard interval in transmitted blocks of signal to avoid inter-block interference (IBI). The most popular methods of the guard interval insertion are zero-padding (ZP) and cyclic prefixing (CP). ZP insert the guard interval at the end of the transmitted blocks of signal, in which all elements are zeros. The length of this interval must be equal to or greater then the channel order. In this way we can avoid IBI, at the expense of lossing the orthogonality between subcarrier due to the multipath channel. However, we can use CP to cope whit this problem. In CP we copy the 25% length at the end of the transmitted blocks of signal, and put it in front of the transmitted block to suppress the inter-block interference and inter-carrier interference.
In this thesis, we consider OFDM system without the guard interval, hence the received signal contains IBI and ICI. In our proposed scheme, we use an oblique projector (OB) to suppress IBI at first. Then we combine it with a generalized sidelobe canceller (GSC) based equalizer [1] for ICI supppression and demodulate the receiver signal.
In computer simulations, we use the GSC-based equalizer with oblique projector to suppress IBI/ICI in the time-invariant channel and time-varying channel. As we will see, in the CP-free OFDM system, the oblique projector can suppress IBI exactly. Moreover we can get better performance in channel with larger order.

中文摘要 . ii

英文摘要 .iii

目錄 iv

圖表目錄 vi

第一章 簡介 1
第二章 傳統正交分頻多工系統簡介 4

2.1 概述 4
2.2 正交分頻多工系統 4
2.2.1 正交分頻多工調變 5
2.2.2 循環前置碼 10
第三章 非正交投影結合廣義旁波帶消除等化器 13

3.1 概述 13
3.2 廣義旁波帶消除等化器 14
3.2.1 非時變通道模型 14
3.2.2 廣義旁波帶消除等化器 16
3.3 非正交投影技術 19
3.3.1 線性模型 19
3.3.2 非正交投影數學模型 20
3.4 非正交投影結合廣義旁波帶消除等化器用於非時變通道環境 24
3.4.1 非時變通道模型 25
3.4.2 非正交投影結合廣義旁波帶消除等化器 27
3.5 非正交投影結合廣義旁波帶消除等化器用於時變通道環境 30
3.5.1 時變通道模型 30
3.5.2 非正交投影結合廣義旁波帶消除等化器用於時變通到環境 33
第四章 電腦模擬 36

4.1 概述 36
4.2 非時變通道環境 36
4.3 時變通道環境 38
第五章 結論 41
參考文獻 42

附錄 44

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