對基於衰減通道的正交分頻多工系統，我們運用具有遞迴均方演算法的頻域等化器來估測信號。本論文採用的衰減通道模型為加入Walsh-Hadamard編碼的修正型傑克模型，我們並以此模型模擬具頻率選擇特性的雷利衰減通道，且都卜勒漂移、頻率偏移和雜訊對系統的影響都會被考慮在其中。我們運用正方形4-QAM的信號於具有16個子通道的正交分頻多工系統做為實驗模擬的基本架構。實驗及討論結果顯示慢速衰減通道整體而言有相當不錯的表現。

For orthogonal frequency division multiplexing (OFDM) systems over fading channels, we apply recursive least-squares (RLS) algorithm to a frequency domain equalizer (FEQ) for signal detection. For fading channel model, we use modified Jakes model with Walsh-Hadamard precoding to simulate frequency-selective Rayleigh fading in our simulation works. Effects on system performance of Doppler spread, frequency offset, and noise are studied. In simulations, square 4-QAM signaling in a 16 subband OFDM system is employed. Study results show that the scheme works well for slow fading channels.

CHINESE ABSTRACT                                                   I
ENGLISH ABSTRACT                                                  II
ACKNOWLEDGEMENT                                               III
CONTENTS                                                           IV
LIST OF FIGURES                                                     VI
CHAPTER 1  INTRODUCTION                                          1
CHAPTER 2  MULTIPATH FADING CHANNELS AND PROPAGATION MODELING                                              5
2.1	Multipath Propagation ……………...…………………….....…... 5
2.2	Rayleigh Fading model……………………………...……………..6
2.3	Other Fading Models…………………………………...…………8
2.3.1	Rice fading…………………….…………...……8
2.3.2	Nakagami fading………………...……...….…...9
2.4	Shadowing………………………………………………………...10
2.5	Frequency Selective and Nonselective (Flat) Fading…………...11
2.6	Modified Jakes Model……………………………………….…...12
CHAPTER 3  QAM SIGNALING SCHEME                               15
3.1  Pulse Amplitude Modulation…………………………………….15
3.2  Phase-Shift Keying……………………………………………….16
3.3  Quadrature Amplitude Modulation……………………….……..17

CHAPTER 4  THE OFDM SYSTEM STRUCTURE                        19
4.1	An Ideal System………………………………………………....19
4.2	OFDM System with Frequency Offset and Additive White Gaussian Noise……………………………………………….….22
CHAPTER 5  THE FREQUENCY DOMAIN RECURSIVE LEAST-SQUARE EQUALIZER                                           26
5.1	Frequency Domain Equalization…………………….………...26
5.2	The RLS FEQ Algorithm………………………………………28
CHAPTER 6  SIMULATION RESULTS AND DISCUSSIONS               32
6.1	Learning Curve Performance…………………...……………32
6.2	Symbol Error Rate Performance……………………………..40
CHAPTER 7  CONCLUSIONS                                         43
7.1	Important Findings………………………………………….…43
7.2	Further Research Possibilities…………………………….......43
REFERENCES                                                        45
LIST OF FIGURES


Figure 4.1 The OFDM system with frequency offset and AWGN………………………...24
Figure 5.1 Bank of linear combining filters……………………………………………….27
Figure 5.2 The RLS FEQ………………………………………………………………….29
Figure 6.1 RLS learning curves for OFDM system over flat fading and frequency-selective fading channels………………………………………………………………...35
Figure 6.2 Effect of carrirer frequency offset on the RLS FEQ performance……………..36
Figure 6.3 Learning curves for a flat fading channel with various Doppler parameters..…37
Figure 6.4 Learning curves for a 2-tap frequency-selective channel with various 
Doppler parameters…..………………………………………………………..38
Figure 6.5 Learning curves for the 2-tap frequency-selective channel as in Figure 6.4 
with same Doppler parameters but high SNR…………………………………39
Figure 6.6 SER performance of the flat fading channel…………………………………...41
Figure 6.7 SER performance of the frequency-selective channel…………………………42

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