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研究生：	蔡慶鴻 Tsai, Ching-Hung
論文名稱：	正交分頻多工系統之線性預先編碼研究 Study in Linear Precoded OFDM Systems
指導教授：	張名先 Chang, Ming-Xian
學位類別：	碩士 Master
系所名稱：	電機資訊學院 - 電腦與通信工程研究所 Institute of Computer & Communication Engineering
論文出版年：	2008
畢業學年度：	96
語文別：	英文
論文頁數：	56
中文關鍵詞：	正交分頻多工系統、零頻譜、置首資料率、線性預先編碼
外文關鍵詞：	linear precoded, data rate overhead, orthogonal frequency division multiplexing (OFDM, spectral nulls
相關次數：	點閱：141 下載：3
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未編碼的正交分頻多工系統(OFDM)是沒有多路徑分集效應(multipath diversity)的，在多路徑瑞利衰減(multipath Rayleigh fading)通道中的分集效應只有1階。爲了減少分集效應的損失，我們介紹了在正交分頻多工系統的線性預先編碼(linear precoded)。我們考慮在有最小位元錯誤率的未編碼正交分頻多工系統和ㄧ正交預先編碼。我們模擬和比較預先編碼正交分頻多工系統在強制歸零(zero-forcing)，最小均方差(MMSE)和最大概率(ML)接收機下的位元錯誤率效能。
當正交分頻多工系統在符號間干擾的通道中(ISI channel)有零頻譜(spectral nulls)時，效能可能會降低。我們研究一種precoded正交分頻多工系統,可以在不知道符號間干擾通道的資訊下仍可以移除零頻譜的影響。當符號間干擾通道長度很長時，ㄧ般正交分頻多工系統的置首資料率(data rate overhead)很高。所以，我們研究有足夠CP，仍在沒有符號間干擾通道影響下的向量正交分頻多工系統(VOFDM)來減少置首資料率(data rate overhead)。

The uncoded orthogonal frequency division multiplexing (OFDM) systems do not have multipath diversity, and the diversity order is only one in the multipath Rayleigh fading channel. To mitigate the loss of diversity, we could introduce linear precoding in OFDM systems. We consider the minimization of uncoded bit-error rate (BER) for OFDM with orthogonal precoding. We simulate and compare the BER performance of the precoded OFDM system with zero forcing, minimum mean squared error (MMSE), and maximum likelihood (ML) receivers.
The performance of OFDM systems may be degraded when intersymbol interference (ISI) channels have spectral nulls. We study an approach of the precoded OFDM system that removes the spectral nulls of an ISI channel without knowing the ISI channel information. When the ISI channel length is large, the data rate overhead of conventional OFDM is large, due to the long CP. Therefore, we also study VOFDM systems to reduce the data rate overhead, in which the ISI channels are transformed to ISI-free channels.

Chinese Abstract	 I
English Abstract	 II
Acknowledgement    III
Contents           IV
List of Figures    VI

Chapter 1 Introduction                                	 1

Chapter 2 OFDM system and Channel Model             	 3
2.1    Introduction to OFDM.............................3
2.2    Conventional OFDM Structure and Basic............4
2.2.1  OFDM Structure...................................4
2.2.2  Generation OFDM signal...........................5
2.2.3  Guard Interval (GI) Insertion....................6
2.3    Channel Model....................................8
2.3.1  Modification of Jake’s Rayleigh Fading model....8

Chapter 3 Linear Precoded OFDM System          	10
3.1    Unitary Precoded OFDM Systems...................11
3.1.1  Zero-forcing receiver...........................11
3.1.2  MMSE receiver...................................20
3.1.3  Simulation results..............................26
3.2    Precoded OFDM Robust to Channel Spectral Nulls Systems................................................32
3.2.1  Performance analysis of the precoded OFDM system.................................................36
3.2.2  Simulation results..............................42
3.3    Unitary Precoded OFDM Robust to Channel Spectral Nulls Systems..........................................46
3.3.1  System describe.................................46
3.3.2  Simulation results..............................48
3.4    Vector OFDM Systems.............................51
3.4.1  System describe.................................51
3.4.2  Simulation results..............................54

Chapter 4 Conclusions 	                           56

Bibliography 	                                    57
                                    

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校內：2011-07-01公開
校外：2011-07-01公開

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