臺灣博碩士論文加值系統

摘 要
因為正交分頻多工技術將資料由多個子載波或稱為子通道平行方式傳送資料，所以調變訊號的振幅可能會產生極大與極小的峰值，使得正交分頻多工系統的調變訊號動態範圍相當大，也就是峰對平均值功率比(Peak-to-average power ratio，PAPR)過高，峰對平均值功率比過高是正交分頻多工技術的主要問題之一，峰對平均值功率比過高導致系統的抗非線性失真能力差，限制了它的進一步推廣應用。
此論文，我們將OFDM傳送接收系統作一些說明，並對於減少OFDM PAPR 的技巧作簡短的討論。最後針對SLM之改變編碼結構方式，如不同的相位序列作模擬測試，另根據不同的相位序列cluster 數目討論然後分析找出最好的組合。且說明藉由選擇性對應序列法應用於載波干涉正交分頻多工，來降低峰對平均值功率比。使用選擇性對應序列將一組經調變後，具有最小PAPR值的CI-OFDM調變信號作為所要傳輸的傳輸信號且在接收端覆蓋這些側邊消息位元來還原原來的傳送序列，以及改善CI-OFDM系統中錯誤的側邊消息來提昇系統的效能。

Abstract
An OFDM signal consists of a number of independently modulated subcarriers, which can cause a large peak-to-average power. Large PAPR make the system difficult to resist the nonlinear distortion, and limites it’s application.
In this thesis, an overview of OFDM system is presented. The schemes of reduction OFDM PAPR are discussed briefly. We focus on the different schemes of SLM scrambling such as different phase sequences, discussed the best combination between different phase sequences and different clusters, and evaluates the peak-to-average power ratio (PAPR) performance in a convolution coded Carrier Interferometry Orthogonal Frequency Division Multiplexing(CI-OFDM) system using the selective mapping (SLM) approach. The proposed SLM-based CI-OFDM system selects the transmitted sequence with the lowest average PAPR over all transmit signal and retrieves the side information very accurately degradation of the PAPR, which can improve the overall detection performance of the CI-OFDM system.

目　錄

第一章 序論..................................... 1
1.1 簡介....................................... 1
1.2 研究背景................................... 3
1.3 研究目的與動機............................. 3
1.4 各章節內容概述............................. 4
第二章 正交分頻多工技術介紹....................... 6
2.1 正交分頻多工技術的發展背景................. 6
2.1.1 正交分頻多工的系統起源.................. 6
2.1.2 正交分頻多工技術的改進與發展............ 7
2.1.3 正交分頻多工系統的應用.................. 8
2.2 正交分頻多工系統的原理..................... 8
2.2.1 正交分頻多工技術的調變模型.............. 9
2.2.2 正交分頻多工技術的正交原理.............. 11
2.3 正交分頻多工系統的優點..................... 13
2.3.1 抗頻率選擇性衰弱........................ 13
2.3.2 OFDM與傳統FDM頻譜比較.................. 14
2.3.3 OFDM與傳統單載波的頻寬使用效率.......... 15
2.3.4 可變的變調方式.......................... 16
2.3.5 抵抗多重路徑干擾與單頻調的實現.......... 17
2.4 同調解調技術應用於正交分頻多工............. 17
2.4.1 垂直振幅調變技巧(QAM)用於正交分頻多工系統 17
2.4.2 相位位移鍵調變技巧(PSK)用於正交分頻多工系統....................................... 20
2.4.3 PSK與QAM的優缺點比較................... 23
第三章 峰對平均值功率比........................... 25
3.1 前言....................................... 25
3.2 基頻數位訊號之峰對平均功率比............... 25
3.2.1 峰對平均功率比.......................... 25
3.2.2 PAPR值機率分佈.......................... 26
3.3 OFDM系統的PAPR降低技術................... 28
3.3.1 過大振幅剪除技術........................ 28
3.3.2 過大振幅剪除技術+峰值視窗技術........... 28
3.3.3 過大振幅剪除技術+濾波器設計技術......... 29
3.3.4 峰值消除技術............................ 29
3.3.5 選擇性映射技術.......................... 29
3.3.6 部份傳輸序列技術........................ 32
3.3.7 編碼型技術.............................. 34
3.3.8 其它技術................................ 35
3.4 過大峰值訊號對功率放大器非線性特性的影響... 36
3.5 結論....................................... 37
第四章 Carrier Interferometry展頻碼技術.......... 39
4.1 CI/OFDM傳送端架構......................... 39
4.2 CI/OFDM接收端架構......................... 42
4.2.1 CI/OFDM接收端基本原理................... 42
4.2.2 QAM CI/OFDM接收端架構................... 45
4.2.3 MMSEC for CI/OFDM with QAM.............. 48
4.2.4 最小均方誤差組合法...................... 49
4.3 PAPR在OFDM和CI/OFDM系統................. 52
第五章 實驗結果與模擬............................. 55
第六章 結論與未來發展............................. 70
參考文獻 ........................................ 72



圖例

2.1 正交分頻多工調變圖......................... 9
2.2 OFDM子載波頻譜圖........................... 12
2.3 OFDM時域訊號圖............................. 12
2.4 通道效應示意圖............................. 14
2.5 OFDM與傳統FDM頻譜比較圖................... 15
2.6 單載波系統頻譜示意圖....................... 15
2.7 正交分頻多工頻譜示意圖..................... 16
2.8 16QAM調變以Gray Code編碼的訊號對映圖...... 19
2.9 16QAM分成兩個4 Array的PSK................ 19
2.10 QPSK調變器................................. 21
2.11 QPSK調變系統訊號空間星雲圖................. 22
2.12 16PSK與16QAM調變系統訊號空間星雲圖........ 23
3.1 選擇性映射傳送端方塊圖..................... 31
3.2 分部傳送序列之示意圖....................... 33
3.3 分部傳送序列傳送端架構圖................... 34
3.4 功率放大器示意圖........................... 37
4.1(a) 傳統OFDM傳送端架構........................ 39
4.1(b) CI/OFDM傳送端架構.......................... 40
4.1(c) CI/OFDM展頻碼操作.......................... 40
4.2 CI/OFDM接收端架構.......................... 43
4.3(c) CI/OFDM傳送訊號............................ 54
5.1 OFDM-BPSK vs CI/OFDM-BPSK之PAPR值......... 56
5.2 OFDM-QPSK vs CI/OFDM-QPSK之PAPR值......... 57
5.3 OFDM-16QAM vs CI/OFDM-16QAM之PAPR值....... 58
5.4 OFDM-64QAM vs CI/OFDM-64QAM之PAPR值....... 59
5.5 OFDM-16QAM和CI/OFDM-16QAM的BER vs. SNR結果................................... 60
5.6 OFDM-64QAM和CI/OFDM-64QAM的BER vs. SNR結果................................... 61
5.7 在AWGN通道上窄頻干擾所得到的OFDM模擬結果....................................... 62
5.8 在AWGN通道上窄頻干擾所得到的CI/OFDM模擬結果..................................... 63
5.9 在頻率選擇衰減通道上窄頻干擾所得到的OFDM模擬結果................................... 64
5.10 在頻率選擇衰減通道上窄頻干擾所得到的CI/OFDM模擬結果.......................... 65
5.11 OFDM vs CI/OFDM的窄頻干擾............... 66
5.12 OFDM vs CI/OFDM vs CI/OFDM with SLM的CCDF對PAPAR值比較...................... 67
5.13 比較在不同的相位序列法所得到的CCDF之PAPR值.................................... 68
5.14 隨機序列在不同的相位序列所得到的CCDF之PAPR值.................................... 69


表格

2.1 OFDM系統載波數比較表 22

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