在本論文中，我們研究通道估計誤差對正交分頻多工系統在多路徑雷利緩慢衰落通道之下之位元錯誤率之影響。由於可加白色高斯雜訊和殘餘載波頻率偏差所引起的載波間干擾，使得基於訓練符號的通道估測不完美。我們使用基於BPSK、QPSK、16-QAM、64-QAM的調變系統下所推導出的位元錯誤率公式，來描述由不完美的通道狀態資訊所導致系統效能降低的特性。而我們所推導出來的位元錯誤率公式不需要複雜的積分計算，可以很容易的計算出結果並且相當的精確。電腦模擬的結果可以驗證我們的理論分析。

In this thesis, we study the effects of channel estimation error on the bit error probability of orthogonal frequency division multiplexing (OFDM) systems in multipath Rayleigh slowly fading channels. The channel estimation errors come from the additive white Gaussian noise (AWGN) and intercarrier interference (ICI) caused by the residual frequency offset (CFO) We derive the bit error rate (BER) formulas for BPSK, QPSK, 16-QAM, and64-QAM modulation schemes to characterize the performance degradation resulting from imperfect channel state information (CSI).  Without complex numerical integrals in our BER formulas, they can be evaluated easily and accurately. Simulation results verify the correctness of our theoretical analysis.

ACKNOWLEDGENMENT                                                I
CHINESE ABSTRACT                                                   II
ENGLISH ABSTRACT                                                  III
CONTENTS                                                            Ⅳ
LIST OF FIGURES                                                      Ⅵ
CHAPTER 1  INTRODUCTION                                          1
CHAPTER 2  WIRELESS CHANNEL TYPES AND RAYLEIGH CHANNEL MODEL                                                  4
2.1	Fading Parameters …………………..…………………….....…... 4
2.1.1	Delay Spread…………….…….…………...……4
2.1.2	Coherence Bandwidth…………...……...….…...5
2.1.3	Doppler Shift……………….……………………5
2.1.4	Doppler Spread………………………………….6
2.1.5	Coherence Time…………………………………7
2.2	The Characteristic of Wireless Channels…………………………7
2.2.1	Flat Fading……………..…….…………...……..7
2.2.2	Frequency Selective Fading……..……...….…...8
2.2.3	Fast Fading………..……………..………………8
2.2.4	Slow Fading………..…………………………….8
CHAPTER 3  OFDM SYSTEMS OVERIEW AND SYSTEM MODEL          10
3.1  Frequency-Division Multiplexing and Orthogonality………….10
3.2  Guard Interval and Cyclic xtension….………………………….12
3.3  System Model……………………………………………….……..13

CHAPTER 4  BER ANALYSIS                                           18
4.1	Background………..……………………………………………....18
4.2	BPSK……………..…………………………………………….….22
4.3	QPSK………………………………………………………………27
4.4	16-QAM……………………………………………………………29
4.5	64-QAM……………………………………………………………33
CHAPTER 5  NUMERICAL RESULTS                                    37
5.1	Simulation Setup…………………..………………….…………..37
5.2	Results…………………………………………………………..…37
CHAPTER 6  CONCLUSIONS                                           47
REFERENCES                                                         48


LIST OF FIGURES


Figure 2.1 Doppler effect……………..………………………………..…………………..6
Figure 2.2 Fading illustration………………..………………..……………………………7
Figure 3.1 Subdivision of the channel bandwidth W………………..……………………11
Figure 3.2 No guard interval (GI) on each symbol…………………………………….....12
Figure 3.3 Add guard interval (GI) on each symbol………………………….…………..12
Figure 3.4 Cyclic extension types……………………………………………………...…13
Figure 3.5 A typical frame structure of OFDM symbols…………………..….…………..14
Figure 4.1 QPSK constellation with Gray encoding………………………………………27
Figure 4.2 16-QAM constellation with Gray encoding.…………………………………...30
Figure 4.3 16-QAM bit-by-bit demapping………………….……..………………………30
Figure 4.4 64-QAM constellation with Gray encoding.…………………………………...36
Figure 4.5 64-QAM bit-by-bit demapping………………………………………………...36
Figure 5.1 Effect of channel estimation error on the BER of BPSK modulated OFDM signals in multipath Rayleigh fading channels.…………..……………..….....41
Figure 5.2 Effect of channel estimation error on the BER of QPSK modulated OFDM signals in multipath Rayleigh fading channels.…………..……………..….....42
Figure 5.3 Effect of channel estimation error on the BER of 16-QAM modulated OFDM signals in multipath Rayleigh fading channels.…………..……………..….....43
Figure 5.4 Effect of channel estimation error on the BER of 64-QAM modulated OFDM signals in multipath Rayleigh fading channels.…………..……………..….....44

Figure 5.5 The BER performance of BPSK, QPSK, 16-QAM, and 64-QAM modulated OFDM signals with different numbers of training symbols……………..….....45
Figure 5.6 The BER performance of BPSK and 64-QAM modulated OFDM signals with three different training sequences………………………………………..….....46

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