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系統識別號 U0002-1806200816073500
中文論文名稱 頻率選擇性通道下正交分頻多工系統之頻率同步與通道估測 : 最大概似率與最小平方估測法
英文論文名稱 Frequency Synchronization and Channel Estimation for OFDM Systems over Frequency-Selective Channels: ML and LS Approaches
校院名稱 淡江大學
系所名稱(中) 電機工程學系碩士班
系所名稱(英) Department of Electrical Engineering
學年度 96
學期 2
出版年 97
研究生中文姓名 南尚傑
研究生英文姓名 Shang-Chieh Nan
學號 695441104
學位類別 碩士
語文別 中文
第二語文別 英文
口試日期 2008-06-16
論文頁數 57頁
口試委員 指導教授-嚴雨田
委員-易志孝
委員-劉鴻裕
中文關鍵字 正交分頻多工  最大概似  都普勒偏移  頻率偏移  頻率選擇性衰退  通道頻率響應 
英文關鍵字 OFDM  Maximum-likelihood  Doppler spread  Carrier frequency offset  Frequency selective fading  Channel frequency response  Gradient search  Inter-symbol interference 
學科別分類 學科別應用科學電機及電子
中文摘要 在本論文中,我們首先介紹正交分頻多工 (orthogonal frequency division multiplexing, OFDM) 傳輸與調變技術的基本原理。其次,我們提出一種最大概似率 (maximum-likelihood, ML) 演算法作聯合頻率偏移與通道頻率響應估測 (joint frequency synchronization and channel estimation)於頻率選擇性通道 (frequency-selective channels)中的OFDM 系統。頻率偏移可能由載波頻率不同步及都卜勒頻譜延展(Doppler frequency spread) 兩者效應所引起。我們使用適應性梯度搜尋法 (adaptive gradient search) 進行頻率偏移的估測,而通道頻率響應 (channel frequency response) 將隨頻率偏移估測後獲得。然後在矯正頻率偏移後,我們再以合理假設運用最小均 (least squares)方法求得通道估測做一比較。我們提出的各種估測法在模擬結果中有十分準確的表現。估測法的模擬結果效能與理論分析之結果十分一致。
英文摘要 In this thesis, we first introduced the basic principle of the orthogonal frequency division multiplexing (OFDM) transmission and modulation technique. Second, we present a maximum-likelihood (ML) estimation algorithm for jointly estimate frequency offset and channel frequency response (CFR) for OFDM systems in frequency selective channels. Then, with proper approximations after frequency offset correction, a least squares approach is also used for channel estimation for comparison. The frequency offset may arise from both carrier frequency mismatch and Doppler spread effect. We use adaptive gradient search to estimate the frequency offset, the channel frequency response estimation is subsequently obtained. Simulation results of our proposed estimations show great estimation accuracies and are found in excellent agreements with theoretical predictions.
論文目次 CONTENTS


ACKNOWLEGENME I
CHINESE ABSTRACT II
ENGLISH ABSTRACT III
CONTENTS IV
LIST OF FIGURE VI
CHAPTER 1 INTRODUCTION 1
CHAPTER 2 OFDM PRINCIPLE AND STRUCTURE 3
2.1 Introduction 3
2.2 Mathematical Description of an OFDM Signal and System 8
2.3 Frequency Offset 11
CHAPTER 3 MULTIPATH PROPAGATION
AND FADING CHANNEL MODELS 17
3.1 Multipath Propagation 17
3.1.1 Frequency Selective and Nonselective (Flat) Fading 18
3.1.2 Slow and Fast Fading Channels 19
3.2 Fading Models 20
3.2.1 Rayleigh Fading Model 20
3.2.2 Rice Fading 22
CHAPTER 4 MAXIMUM LIKELIHOOD ESTIMATION 23
CHAPTER 5 JOINT FREQUENCY SYNCHRONIZATION
AND CHANNEL ESTIMATION 27
5.1 Doppler Spread and Carrier Frequency Offset 27
5.2 The Joint Maximum Likelihood Estimation 30
5.3 A Least squares Approach for Channel Estimation 35
5.4 Channel Estimator Performances 37
CHAPTER 6 NUMERICAL RESULTS 40
CHAPTER 7 CONCLUSIONS 54
REFERENCES 55

LIST OF FIGURE


Figure 2.1.1 Data transmission using multicarriers 4
Figure 2.1.2 Guard Interval protect 5
Figure 2.1.3 Concept of cyclic prefix 6
Figure 2.1.4 Illustration of a frequency selective channel………......................……..….7
Figure 2.2.1 Baseband OFDM Transmitter 9
Figure 2.2.2 Baseband OFDM Receiver (cyclic prefix removal omitted) 12
Figure 2.2.3 The OFDM system structure……………………………………………...16
Figure 6.1 Learning curve of gradient search for frequency offset estimation. 20dB SNR…………………...…….........………………………………….....…42
Figure 6.2 Learning curve of gradient search for estimate frequency offset, and SNR is 40dB. ..……………………………………………………………....……43
Figure 6.3 Estimated frequency offset vs. true frequency offset. SNR is 20. 44
Figure 6.4 Variance of the frequency offset estimator vs. SNR. 45
Figure 6.5 The ML estimate of vs. SNR and the true (solid lines) 46
Figure 6.6 The ML estimate of vs. SNR and the true (solid lines). 47
Figure 6.7 Comparison of the ML estimator variance and the theoretical LS estimator variance for . 48
Figure 6.8 Comparison of the ML estimator variance and the LS estimator variance for . ........................................................................................................49
Figure 6.9 The LS estimate of and the true (solid lines). 50
Figure 6.10 The LS estimate of and the true (solid lines). 51
Figure 6.11 Comparison of the experimental LS estimation variance and theoretical LS estimation variance for . 52
Figure 6.12 Comparison of the experimental LS estimation variance and theoretical LS estimation variance for . 53

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[4] M. Morelli, C.-C. Jay Kuo, Man-On Pun, “Synchronization Techniques for Orthogonal Frequency Division Multiple Access (OFDMA):A Tutorial Review” Proceeding of the IEEE, pp. 1394 – 1427, July 2007
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