臺灣博碩士論文加值系統

　正交分頻多工(OFDM)是ㄧ種非常適合高資料量的無線傳輸的技術。具有許多優點，例如高頻寬效益、高資料傳輸量、抗通道衰弱、抗脈衝干擾、較少非線性失真等等
　　雖然正交分頻多工技術有這麼多的優點，但不可避免地，它也有個嚴重的缺點。OFDM一個主要的缺點就是他有很高的均峰值（PAPR），很高的PAPR值通過線性放大器會產生非線性失真，導致相鄰子載波產生干擾而失去正交性。選擇性映射(Selective Mapping)簡稱SLM是ㄧ種使用在正交分頻多工(OFDM)中有效解決過高均峰值(PAPR)的技術。然而，選擇性映射(SLM)有ㄧ個很嚴重的缺點，那就是該方法的計算複雜度很高。在這篇論文裡，提出的方法使用了改良過的選擇性映射(SLM)方法,並且使用了華式哈達碼轉換(WHT)，能夠有效率地解決均峰值（PAPR）過高以及計算複雜度的問題。從這篇的模擬結果顯示，這裡提出的方法使用華式哈達碼轉換(WHT)可以達到與傳統的選擇性映射(SLM)方法幾乎完全ㄧ樣的降低均峰值（PAPR）的效果又能降低運算的複雜度。

Orthogonal Frequency Division Multiplex (OFDM) is a very suitable technique for achieving high-rate wireless data transmission. High spectral efficiency, robustness to channel fading, immunity to impulse interference and less non linear distortion are among the favorite properties of OFDM.
One major drawback of OFDM is high Peak to Average Power Ratio (PAPR) of the transmitted signal. The high peaks of an OFDM signal are distorted nonlinearly by the high power amplifier (HPA) because the HPA heavily distorts all signal parts that come close to or exceed saturation. The distortion causes inter carrier interference (ICI) and out-of-band (OOB) radiation. While ICI disturbs the transmitted signal, it degrades the bit error rate (BER). OOB radiation disturbs signals on adjacent frequency bands, so it should be avoided.
Several methods have been proposed in the literature to reduce the peak power of OFDM signals and substantial gains were reported. SLM (selective mapping) method is one of the efficient methods to reduce PAPR in OFDM system. However, SLM method has a serious disadvantage high calculation complexity. In this thesis, the proposed method using modified SLM scheme with WHT (Walsh Hadamard transform) to lower the high PAPR of OFDM system and lower the calculation complexity effectively

ACKNOWLEDGMENT I
摘要 II
Abstract III
Contents IV
LIST OF FIGURES VI
LIST OF TABLES IX
CHAPTER 1 INTRODUCTION 1
CHAPTER 2 CONCEPTS OF OFDM TECHNIQUE 4
2.1 Introduction to OFDM Communication System 4
2.2 Bandwidth Efficiency 5
2.3 System Diagram 7
2.4 Multi-carrier Transmission and Orthogonal Consideration 8
2.5 Guard Interval and its Theory 11
2.6 Peak Power Problem of OFDM System 13
CHAPTER 3 PAPR REDUCTION THEORY 16
3.1 Introduction to Peak-to-Average Power Ratio 16
3.2 PAPR Reduction Techniques in OFDM 18
3.3 Clipping and Peak Windowing Introduction 20
3.4 Coding Introduction 23
3.5 Partial Transmit Sequences Scheme (PTS) 24
3.6 Selected Mapping (SLM) 26
CHAPTER 4
SELECTIVE MAPPING SCHEME COMBINUNG WITH Walsh HADAMARD TRANSFORM 29
4.1 A Modified SLM Scheme for PAPR Reduction of OFDM Systems 29
4.2 The SLM with WHT Scheme for PAPR Reduction 35
4.3 The proposed scheme for PAPR reduction of OFDM systems 38
CHAPTER 5 CONCLUSIONS 46
REFERENCES 47

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