臺灣博碩士論文加值系統

由於數位通訊系統的蓬勃發展，對於有限頻寬有越來越高的使用率，因此相鄰頻帶的干擾狀況越來越常發生，這個問題倍受重視。
OFDM在不同符號之間的不連續，會導致頻帶外的功率發散，這些發散會對鄰近頻道造成干擾，並降低頻帶內的訊號品質。
為了降低頻帶外的功率發散，本論文提出, 藉由空的子載波傳送一些額外資料，以保持兩個不同邊界符號間的連續性。除此之外，也不需增加額外的子載波傳遞資料，而是使用原本就沒有傳送資料的子載波，這樣就不需變動原有的規格。且當套用此方法到採用現有OFDM的系統上時，也不需要增加新的硬體，或改變目前原有的通訊協定。
我們將此降低方法,試在一個雷瑞衰減通道模擬工作狀況。模擬的結果顯示，此降低方法確實能降低鄰近頻道的干擾，並提升訊號的品質。

Because of several flourishing development of communication system, as to limited to have high rate of utilization more and more while being wide frequently, so the interference state of the adjoint frequency band more and more takes place often, this question is being paid attention to.
And the discontinuity between different symbols of OFDM, will cause the power outside of the frequency band to disperse, these are dispersed will cause and interfere to near the channel, and reduce the signal quality in the frequency band.
Disperse for the power of reducing outside of the frequency band, by using the null subcarrier to convey the extral information that would make continuity among successive symbol border. Above all, this modification do not have to change any part of the specific standard, that means this approach is compatible with existing system.
A Rayleigh fading channel is applied to verify our proposed alogorithm. The simulation result shows, the proposed algorithm can reduce the channel interference, and improve the quality of the signal even in the fading channel.

ACKNOWLEDGMENTS I
ABSTRACT II
摘要 III
TABLE OF CONTENTS IV
LIST OF FIGURES VI
LIST OF TABLES IX
CHAPTER 1 INTRODUCTION 1
1.1 Introduction 1
1.2 Motivation 2
1.3 Organization of This Thesis 3
CHAPTER 2 IEEE Standard 802.11a Specification 4
2.1 Introduction to OFDM 4
2.2 Architecture of OFDM system 5
2.3 Advantages of OFDM 6
2.3.1 Multipath Delay Spread Tolerance 6
2.3.2 Effectiveness against Channel Distortion 6
2.3.3 Throughput Maximization (Transmission at Capacity) 7
2.3.4 Robustness against impulse response 7
2.4 OFDM Parameters in IEEE 802.11a Standard [2] 8
2.4.1 OFDM PHY specification for the 5 GHz band 8
2.4.2 OFDM Physical Layer Convergence Protocol (PLCP) sublayer 11
CHAPTER 3 CHANNEL MODEL AND OUT-OF-BAND POWER REDUCTION 19
3.1 Introduction to Channel Model 19
3.2 Additive White Gaussian Noise (AWGN) 19
3.3 Fading Channels 23
3.3.1 Mobile Radio Propagation 23
3.3.2 Small-Scale Fading 26
3.3.3 Doppler Shift 28
3.3.4 Types of Small-Scale Fading 29
3.4 Rayleigh and Ricean Fading Distribution 36
3.5 Simulation of Rayleigh Fading Channel 37
3.6 Introduction to Out-of-Band Power 40
3.7 Comparison of Frequency Descending Rate 42
3.8 The Zero-Forcing (Smooth Order 0&1) Method [3] 43
3.9 The Tail-Tracking Method [4] 50
3.10 The peak-power Phenomenon and constraint method 52
CHAPTER 4 SIMULATION RESULTS 54
4.1 Introduction 54
4.2 The Results in One-Ray Fading Channel Model 55
4.3 The Results in Two-Ray Fading Channel Model 64
4.4 PAPR 73
CHAPTER 5 CONCLUSIONS 78
REFERENCES 79

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