臺灣博碩士論文加值系統

為了減少過大峰均功率比值 (PAPR) 造成的非線性效應，我們可將傳送信號經過波峰削減來降低峰均功率比值。這類降低峰均功率比值的技術適用在將過大訊號波峰變成較理想訊號波峰且有效星座圖擴展 (ACE) 是波峰削減技術中的一種。
ACE方法是利用削減峰值和修正星座點到所設定的位置來有效降低OFDM系統中的PAPR值。有效星座圖擴展智慧型梯度投影法 (ACE-SGP) 則是考慮一個clip noise的梯度下降方向並且在疊代過程中選擇較佳的步階大小來減少PAPR。ACE-SGP比ACE有更快的收斂速度。上述兩種方法在接收端皆不需加裝額外的解調裝置。本次提出方法稱為有效星座圖擴展外接圓法 (ACE-CC)。藉由設定不同峰值的調整係數以及執行一個外接圓限制來修正星座圖點來獲得更顯著的PAPR值降低效果並且其位元錯誤率尚能在可接受的範圍。ACE-CC與上述兩方法相同皆不需在接收端加裝額外裝置。

In order to alleviate large peak-to-average power ratio (PAPR) cause the nonlinear effects, we can apply to transmission signal pass through peak cancellation to reduce PAPR. Peak cancellation class of PAPR reduction techniques applies large signal peaks to the desired signal peaks and Active Constellation Extension (ACE) is among the peak canceling techniques.
ACE method is the clipping peak value and modified constellation points to set up location to effective reduce PAPR in OFDM. Active Constellation Extension - Smart Gradient Project (ACE-SGP) approach is considering the clipped noise to be gradient-descent direction and choosing a very good step size in iteration to reduce PAPR. ACE-SGP method converge faster than ACE method. Above two methods have not the requirement of additional devices in receiver. In this thesis, we proposed the method called Active Constellation Extension - Circumcircle (ACE-CC) method. By set up different adjust ratio of signal peak value and enforce circumcircle constrain to modified constellation points. It can be obtain conspicuous PAPR reduction and acceptable BER. Like above two methods, ACE-CC does not require additional device in receiver.

Abstract in Chinese…………………………………………………………………….i
Abstract in English…………………………………………………………………….ii
Acknowledgment in Chinese…………………………………………………………iv
Contents………………………………………………………………………………..v
List of Figures………….…………………………………………………………….vii
Chapter 1 Introduction………………………………………………………………...1
Chapter 2 Basic Principles…………………………………………………………….3
2.1 Principle of Orthogonal Frequency Division Multiplexing…………….3
2.1.1 OFDM Systems Model………………………………………..…..4
2.1.2 Guard Interval and Cyclic Prefix………………………………….7
2.2 The Challenges of OFDM Systems……………………………………..8
2.2.1 Frequency Offset………………………………………………….8
2.2.2 Peak-to-Average Power Ratio…………………………………...11
2.3 Methods to reduce PAPR in OFDM Systems………………………….14
2.3.1 Amplitude Clipping Method……………………………………..14
2.3.2 Selected Mapping Method………………………………………15
2.3.3 Partial Transmit Sequence Method……………………………...16
2.3.4 Tone Reservation Method………………………………………..17
Chapter 3 Modified of Active Constellation Extension Technique………………..…19
3.1 Active Constellation Extension Method……………………………….19
3.2 ACE - Smart Gradient Project Method………………………………..26
3.3 ACE – Circumcircle Method…………………………………………..33
Chapter 4 Simulation Results………………………………………………………...38
4.1 Compare ACE-CC with ACE………………………………………….38
4.2 Performance of ACE-CC with different adjust ratio……………..……40
Chapter 5 Conclusions……………………………………………………………….46
References……………………………………………………………………………48

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