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系統識別號 U0002-1806200815112500
中文論文名稱 正交分頻多工系統在頻率平坦通道中之頻率同步和通道估測研究利用最大概似率與最小平方估測法之研究
英文論文名稱 Frequency Synchronization and Channel Estimation for OFDM Systems over Frequency-Flat 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 洪明志
研究生英文姓名 Ming-Chih Hong
電子信箱 h91304001@hotmail.com
學號 695441096
學位類別 碩士
語文別 英文
口試日期 2008-06-16
論文頁數 43頁
口試委員 指導教授-嚴雨田
委員-劉鴻裕
委員-易志孝
中文關鍵字 正交分頻多工系統  最大概似估計法  載波頻率偏移  都卜勒展延  最小平方法 
英文關鍵字 Orthogonal frequency division multiplexing (OFDM)  maximum-likelihood (ML) estimation  carrier frequency offset (CFO)  Doppler spread  least squares 
學科別分類 學科別應用科學電機及電子
中文摘要 正交分頻多工系統是新的調變技術用來抵抗多路經衰減效應。IEEE802.11a將OFDM定為標準規格。OFDM系統的一些優點:如降低計算複雜度、對抗窄頻干擾的能力、頻率分級的利用等等。在這篇論文中,我們考慮聯合頻率偏移和通道估測,但是我們先假定時間同步化的工作已經完成了。OFDM系統是在一個頻率平坦的環境下所做的。在這裡我們提出使用最大概似(ML)估計演算法來做聯合頻率偏移和通道估測。模擬的步驟:我們利用梯度圖來求得頻率偏移估測,再根據頻率偏移估測來求得通道頻率反應。然後在矯正頻率偏移後,我們再以合理假設運用最小平方法(least squares)求得通道估測做一比較。最後再將理論值跟模擬作比較。
英文摘要 Orthogonal frequency division multiplexing (OFDM) is a new generation modulation technique. OFDM system is robust against the fading effects of multipath propagation. The IEEE 802.11a applies OFDM for wireless local area networks (WLAN) as standard specification. OFDM has several advantages :reduced computational complexity、exploitation of frequency diversity、and robust against narrowband interference. In this paper, we consider joint frequency offset and channel estimation assuming timing synchronization has been completed .Flat fading channels are considered. We use a maximum-likelihood (ML) algorithm to jointly estimate the frequency offset and the channel frequency response (CFR). By first obtaining the frequency offset estimation using gradient plot, then the CFR estimation is obtained from the frequency offset estimation result. Further, an alternative approach using a least squares formulation for channel estimation is also presented based on completion of the frequency offset correction. Simulations are performed to compare with theoretical predictions.
論文目次 CONTENTS

ACKNOWLEDGENMENT I
CHINESE ABSTRACT II
ENGLISH ABSTRACT III
CONTENTS IV
LIST OF FIGURES VI
CHAPTER 1 INTRODUCTION 1
CHAPTER 2 MOBILE WIRELESS CHANNELS 4
2.1 Doppler Spread and Channel Coherence Bandwidth 4
2.2 The Rayleigh Fading Model 6
CHAPTER 3 PRINCIPLES AND STRUCTURE OF ORTHOGONAL FREQUENCY DIVISION MULPLEXING SYSTEMS 8
3.1 The Multicarrier System Model 9
CHAPTER 4 MAXIMUM LIKELIHOOD ESTIMATION 14
CHAPTER 5 FREQUENCY SYNCHRONIZATION AND CHANNEL ESTIMATION 18
5.1 Signal and System Models 18
5.2 The Joint Maximum-likelihood Estimation Algorithm 21
5.3 A Least Squares Channel Estimation 25
5.4 Channel Estimator Performance 27
CHAPTER 6 NUMERICAL SIMULATIONS 29
CHAPTER 7 CONCLUSIONS 39
REFERENCES 40

LIST OF FIGURES

Figure 3.1 The OFDM system structure…………………………………………………13
Figure 5.1 Gradient curve………………………………………………………………..24
Figure 6.1 Estimated frequency offset vs. true frequency offset for two SNR values 31
Figure 6.2 Estimated frequency offset vs. SNR for a true offset of 0.2. 32
Figure 6.3 ML Frequency offset estimation variance vs. SNR for . 33
Figure 6.4 Variance of the ML frequency offset variance vs. true offset. SNR 40dB …..34
Figure 6.5 ML estimate of vs. SNR……………….……………………………….35
Figure 6.6 LS estimate of vs. SNR…………………………..…………………….36
Figure 6.7 Comparison of the ML channel estimation variance and the theoretical LS
estimation variance…………….…………………………………………..…37
Figure 6.8 Comparison of the LS channel estimation variance and the theoretical LS estimation variance…………………………………...………………………38




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