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研究生:葉柏佟
研究生(外文):Ye Bo-Tong
論文名稱:頻域通道等化器在OFDM系統接收端之研究探討及系統規劃
論文名稱(外文):The study and system configuration of frequency-domain channel equalization in OFDM receiver
指導教授:廖和恩
指導教授(外文):LIAO HO-EN
學位類別:碩士
校院名稱:逢甲大學
系所名稱:電機工程學系
學門:工程學門
學類:電資工程學類
論文種類:學術論文
論文出版年:2001
畢業學年度:89
語文別:中文
論文頁數:60
中文關鍵詞:正交分頻多工(OFDM)通道等化器多重路徑干擾符間干擾(ISI)保護頻帶
外文關鍵詞:Orthogonal Frequency Division Multiplexing(OFDM)Channel equalizerMulti-pathInter-symbol Interference(ISI)Guard interval
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多載波調變的技術如正交分頻多工(OFDM),目前已廣泛的被應用在高傳輸無線行動通訊上。隨著多媒體時代的來臨,大量的影像資料傳送將使得高位元率要求相對的提高,因此多路徑通道所引起的符間干擾將更加明顯。在早期,時域通道等化器已大量的被應用在衰減通道補償上,但是一般而言等化器均需有相當的階數,如果在高傳速要求下將使其設計更趨於複雜、困難;另一方面就OFDM系統而言,保護頻帶(guard interval)的設計雖然可以克服這方面的問題,卻降低整個系統的傳輸效益。相對的若以頻域來處理則不但收斂速度較為快且濾波器所需的階數也較為低;另外頻域的計算複雜度也較低。更者,由於OFDM的傳送基本上可以先做IFFT,再做載波調變來達成,因此我可將此多載波的調變結果視為多個頻率成份的信號,故若在接收端在解調變之後且在做FFT之後,若能以頻域的等化器做通道等化處理則可減少系統的複雜度且應有較佳的等化效果。因此本計劃我們在接收端將提出頻域通道等化器的方式將其建構在OFDM系統上,針對以上的缺失加以改善,使其達到高效率、高品質的需求。

The technology of multi-carrier modulation, such as Orthogonal Frequency Division Multiplexing (OFDM), has been adopted for high-speed data wireless mobile communication. As multimedia age is coming, the transmission of a large number image data will need higher data rate. At the same time, the problem of inter-symbol interference (ISI) becomes more and more serious and needs more care about it. In previous implementation of channel equalizer, time-domain adaptive filters are usually adopted to resolve ISI. Though the time-domain implementation is very straightforward and easy, the order required for the filter is generally high and the computation effort is heavy. Therefore, for high rate data transmission, time-domain implementation of channel equalization becomes more and more complex. In OFDM systems, guard bands are appended after data to mild the effect of ISI, but the system efficiency is lowered down. On the other hand, the frequency-domain implementation of channel equalizers has the advantages of fast converge rate and lower computation effort. It is thus considered in this research proposal for equalization in OFDM systems. Moreover, because the transmitting signal in an OFDM system is basically through IFFT and then multi-carrier modulated, the transmitted signal can be recognized as multi-components (frequency beams) one.
Hence it is intuitive to think of the use frequency-domain equalizer for channel equalization, which occurs between the carrier demodulation and FFT. This may be expected to lower the system complex and have better performance in channel equalization. Thus it is our purpose to design and configure an OFDM system using frequency-domain implementation for channel equalization.

中文摘要……………………………………………………………………i
Abstract……………………………………………………………………ii
致謝…………………………………………………………………………iv
目錄…………………………………………………………………….……v
第一章 緒論……………………………………………………………….1
1.1 研究背景………………………………………………………….....1
1.2 研究方法與進行步驟…………………………………………….....6
第二章 多重路徑傳輸通道分析…………………………………………. 10
2.1多路徑干擾(Time-spreading)分析、定義 .……………………11
2.1.1最大路徑延遲( )………………………………………….11
2.1.2同調頻寬( )……………………………………………….14
2.2多路徑干擾(Time-variant)分析、定義…………………………14
2.2.1都卜勒位移(Doppler shift )&同調時間( )…………..14
2.3衰減通道的分類……………………………………………….….15
2.3.1平坦衰減通道(Flat fading channel)………………… 15
2.3.2頻率選擇衰減通道(Frequency selective fading channel)..16
2.3.3快速衰減通道(Fast fading channel)……………………17
2.3.4緩慢衰減通道(Slow fading channel)……………………17
第三章 多載波調變及本文系統架構設計…………………………… 20
3.1傳統數學的模型描述OFDM訊號………………………………........20
3.1.1垂直正交…………………………………………………….....20
3.1.2 OFDM的實現……………………………………………........22
3.2典型的COFDM系統架構……………………………………….........24
3.2.1錯誤更正碼(Error-correction codes)……………………...24
3.2.2交錯(Interleave)……………………………………………...25
3.2.3保護區間(Guard interval)…………………………………...25
3.2.4系統參數探討……………………………………………….....27
3.3本文主要的架構規劃……………………………………………......28
3.3.1頻域通道等化器在OFDM系統的規劃………………….........28
3.3.2 Over-sampling…………………………………………….....31
3.3.3結合Over-sampling概念在OFDM系統分析……………........35
第四章 模擬與實驗分析……………………………………………….39
第五章結論………………………………………………………………47
參考文獻…………………………………………………………………...48

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