編碼正交分頻多工系統在頻率選擇性衰落通道下等化與資源分配效應

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研究生：	白忠民 Chung-Min Bai
論文名稱：	編碼正交分頻多工系統在頻率選擇性衰落通道下等化與資源分配效應 Effects of equalization and resource allocation in coded OFDM systems over frequency selective fading channels
指導教授：	賴坤財 Kuen-Tsair Lay
口試委員:	方文賢 Wen-Hsien Fang 李大嵩 Ta-Sung Lee
學位類別：	碩士 Master
系所名稱：	電資學院 - 電子工程系 Department of Electronic and Computer Engineering
論文出版年：	2007
畢業學年度：	95
語文別：	中文
論文頁數：	64
中文關鍵詞：	正交分頻多工、渦輪等化、能量分配、子載波選擇
外文關鍵詞：	orthogonal frequency division modulation (OFDM), turbo equalization, energy allocation, sub-carrier selection
相關次數：	點閱：177 下載：5
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無線通訊已成為現今行動通訊中的一大熱門議題。以正交分頻多工(OFDM)為核心的技術不斷的發展，它的各項優勢被廣泛的利用在新穎的標準無線通訊規格上。對於資料的傳輸而言，受到雜訊嚴重和多路徑衰減干擾的通道中傳輸，如何將信號估測並解調使錯誤率降低是研究的主題。等化技術與通道編碼是對抗多路徑干擾常見方式。在本論文中，我們以一種利用線性等化器與解碼器所組成的迭代系統為對照，並且與等接收能量分配與子載波選擇的機制比較在正交分頻多工系統上的表現。並經由電腦模擬驗證上述所有技術在多路徑衰減通道中的效能。

在線性最小均方根(LMMSE)渦輪等化器中，我們使用正交分頻多工的循環字首避免前後框架的干擾影響。而線性最小均方根等化器適用於此系統並比MAP方式擁有較低複雜度，可以進一步等化多路徑效應，與解碼器搭配討論渦輪迭代的效能。此外，本論文應用了等接收能量分配依據通道效應在傳送端對信號分配能量，以取長補短的方式改善系統效能。由於通道所造成信號十分嚴重的信號衰減，利用子載波選擇建立一接收端的回傳機制告知傳送端可用子載波，得到以較低傳輸速率換取穩定傳輸和較低的錯誤率。

Wireless communication has become a popular topic in recent mobile communication. Orthogonal frequency division modulation (OFDM) based approach is investigated continuously. It has many advantages and suits to novel wireless communication standards. In data transmission, how to estimate and decode the signal for reducing the bit error rate (BER) would be the subject for studying. Equalization and channel coding are familiar approaches to combat the multi-path effect. In this thesis, we compare the performance on OFDM systems between the iterative system, which consists of linear equalization and decoder, and the method with equal received energy allocation and sub-carrier selection. From the above mentioned approaches, we do some computer simulations and observe the performances.

We use the cyclic prefix in OFDM to avoid the ISI effect from preceding frames at the LMMSE (linear minimum mean square) turbo equalization scenario. LMMSE equalizer is applicable to OFDM system and has lower complexity than MAP equalizer. It can combine with the decoder on each iteration and equalize the ISI effect further. Besides, we use equal received energy allocation to overcome the weakness of some deep fading sub-channels. We select the strong sub-channels. Then, we allocate energies to them with the knowledge of the channel state information (CSI). Transmitted signal suffers from deep fading, which causes very serious attenuation. We can utilize the sub-carrier selection algorithm from receiver to transmitter to provide better BER performance, at the expense of lower data transmission rate.

第一章	緒論………………………………………………………………… 1
1	引言………………………………………………………1
2	研究動機…………………………………………………2
3	本文架構…………………………………………………3

第二章	相關理論介紹…………………………………………………………4
1	無線通道特性描述 ………………………………………4
2	通道編碼 …………………………………………………5
2.1	迴旋碼 ……………………………………… 6
2.2	交錯器 ……………………………………… 7
3	正交分頻多工系統簡介………………………………… 9
3.1	正交分頻多工系統優點………………………9
3.2	正交分頻多工系統架構………………………10
3.2.1	串列轉並列……………………… 11
3.2.2	反傅立葉轉換…………………… 12
3.2.3	循環字首………………………… 14
3.2.4	正交分頻多工接收端…………… 16
4	渦輪等化器…..………………………………………… 16
5	最小均方根等化器……………………………………… 20
5.1	信號估測基於最小均方差準則………………21
5.2	計算等化器軟輸出機率值……………………24
6	BCJR演算法……………………………………………… 26

第三章	正交分頻多工系統使用注水能量分配和子載波選擇………………30
1	傳送架構………………………………………………… 30
2	道道模型………………………………………………… 31
3	接收架構………………………………………………… 32
3.1	正交分頻多工與渦輪等化器…………………33
3.2	正交分頻多工與渦輪等化器和子載波選擇…36
3.2.1	子載波選擇……………………… 36
3.2.2	正交分頻多工與渦輪等化器和子載波選擇	38
3.3	正交分頻多工與子載波選擇…………………………	39
3.4	正交分頻多工與子載波選擇和注水能量分配………	39
3.4.1	正交分頻多工系統在頻率衰落通道分析…	39
3.4.2	注水能量分配………………………………	44
3.4.3	正交分頻多工與子載波選擇和注水能量分配……………………………………………	47
3.5	正交分頻多工與子載波選擇和注水能量分配搭配BCJR解碼器……………………………………………	48

第四章	實驗結果與討論 ……………………………………………………49
1	實驗環境及參數的設定…………………………………49
2	二位元傳輸正交分頻多工模擬結果……………………51
3	時域和頻域最小均方差渦輪等化器模擬結果…………52
4	正交分頻多工與渦輪等化器模擬結果…………………54
5	正交分頻多工與渦輪等化器和子載波選擇模擬結果…56
6	正交分頻多工與子載波選擇模擬結果…………………58
7	正交分頻多工與子載波選擇和注水能量分配模擬結果59
8	正交分頻多工與子載波選擇和注水能量分配搭配BCJR解碼器模擬結果……………………………………………	60

第五章	結論…………………………………………………………………	62

參考文獻…………………………………………………………………………64

                                

[1] R. Prasad, OFDM for Wireless Communications Systems. John Wiley, 2004.

[2] J. G. Proakis, Digital Communication. 4th ed., McGraw-Hill, 2001.

[3] M. Tuchler, R. Koetter, and A. Singer, “Turbo equalization: Principles and new results,” IEEE Trans. Comm., vol. 50,pp.754-767,May 2002.

[4] M. Tuchler, R. Koetter, and A. Singer, “Minimum Mean Squared Error Equalization Using A Priori Information,” IEEE Trans. on signal processing, vol. 50, no. 3, March 2002.

[5] M. Tüchler, and J. Hagenauer, “Turbo equalization using frequency domain equalizers,” Proc. of the Allerton Conference, Oct. 2000.

[6] Y. Li, S. McLaughlin, and D. G. M. Cruickshank, “OFDM System with Cyclic Prefix Reconstruction and MMSE Turbo Equalization,” IEEE, 2005.

[7] L. R. Bahl, J. Cocke, F. Jelinek, and J. Raviv, “Optimal decoding of linear codes for minimizing symbol error rate,” IEEE Trans. Inform. Theory, Vol. IT-20, pp. 284-287, Mar. 1974.

[8] Y. Rong, S. A. Vorobyov, and A. B. Gershman, “Adaptive OFDM Techniques With One-Bit-Per-Subcarrier Channel-State Feedback,” IEEE Trans. Comm., vol. 54, no. 11, May 2002.

[9] D. Z. Filho, L. Fety, and M. Terre, “Water-Filling for Cyclic Prefixed Single Carrier transmission and MMSE receiver,” European Wireless, April 2007.

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