正交分頻多工通訊中之盲目頻域等化器; The Blind Frequency-Domain Equalizer in OFDM Communications

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Title:	正交分頻多工通訊中之盲目頻域等化器;The Blind Frequency-Domain Equalizer in OFDM Communications
Authors:	龍緒祥;Syu-Siang Long
Contributors:	電機工程研究所
Keywords:	正交分頻多工;快速傅利葉轉換;頻域等化器;FEQ;OFDM;FFT
Date:	2005-07-08
Issue Date:	2009-09-22 11:57:45 (UTC+8)
Publisher:	國立中央大學圖書館
Abstract:	近幾年來，多載波調變技術在現代通訊系統中之應用，有越來越被重視的趨勢，許多新發展出來的有線或無線傳輸系統都偏向於採用此種調變技術，而正交分頻多工即是其中的一種多載波調變技術。利用多個互相正交的子載波通道，能夠有效抵抗通道之多重路徑延遲與頻率選擇性失真效應。在有限傳輸頻寬下，達到有效利用頻寬以及高速資料傳輸的目的。一般在採用正交分頻多工的系統中，為了使符碼通過通道時的失真能完全消除，於是在接收端會採用時域加上頻域等化器之設計。而在歐洲DVB-T系統標準中，由於沒有訓練樣本來訓練時域等化器係數，因此所採用的等化器僅有頻域等化器。為了將頻域等化器係數收斂至最小誤差，最基本的演算法是LMS演算法，然而LMS演算法的收斂條件需要針對每個子通道來求得適當的Step-size，當子通道數目增加的時候，Step-size之求得將會非常繁雜，且收歛速度將不一致。因此，我們提出了一套植基於自動增益控制與載波回覆概念之改進的盲目頻域等化器演算法，針對沒有訓練樣本的系統，如DVB-T系統，使頻域等化器的每個子通道係數能夠快速收歛並且具有良好的通道雜訊抵抗能力。同時具有只要單一的Step-size參數，即可使所有的子通道在相同的時間下收斂。因此，本論文將在歐洲DVB-T標準所訂定的系統環境與通道下，模擬LMS演算法以及所提出的AGC-CR　based演算法之間的收斂過程差異與收斂速度之比較。 Recently, MCM technique has played more important role in the applications of modern communications. OFDM is one of them which can perform better performance of resisting the effects of multi-path channel delay and frequency-selected distortion. With many orthogonal sub-carriers, it can achieve high data rate and has bandwidth efficiency. To remove the multi-path channel effects, time and frequency domain equalizers are applied in the receiver. Because there are no training patterns defined in the Europe DVB-T standard, there is only an FEQ applied in the DVB-T receiver. In the literature, LMS algorithm is the common algorithm to converge the coefficients of FEQ to the minimum error, but it needs computing the proper step-size for each sub-channel to satisfy convergent rule. Besides, convergent speeds of all sub-channels will not be all the same with LMS algorithm, especially when the sub-channel number is large. According to that reason, for OFDM systems without training patterns such as DVB-T system, we proposed an improved blind equalization algorithm based on AGC and Carrier-Recovery techniques to have high convergent speed and resistant ability to the channel effect. This algorithm needs only single step-size for all sub-channels to have high and equal convergent speed. In this thesis, we will observe the convergent speed and channel resistant ability of LMS and proposed algorithms under Europe DVB-T standard.
Appears in Collections:	[Graduate Institute of Electrical Engineering] Electronic Thesis & Dissertation

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