正交分頻多工系統具有高頻寬效能及有效對抗多重路徑干擾之優點，因此成為現今主要的無線通訊規格之一。但其主要的缺點為具有高峰均功率比，這個問題會使經過功率放大器的訊號，因非線性效能引起失真造成放大器功率效率的降低。因此降低峰均功率比值為現今研究的焦點。
在本篇論文中，將會探討兩種降低峰均功率比的技術。首先是以相位轉向技術來討論，可以延伸出兩種改進的方法。其一針對相位轉向技術的需要旁資訊的修正來改進，其二增加相位轉向技術的降低峰均功率比的效能。再來把這兩種改進的方法結合，並討論其優缺點。另一主題討論頻道保留技術，改進基本的頻道保留技術，使得能獲得更佳的降低峰均功率比的效能，並且把該項技術，放入正交分頻多工存取系統。最後將以上提出的幾種技術進行電腦的模擬及分析。並比較其性能。

Orthogonal frequency division multiplexing (OFDM) scheme with high spectral efficiency and resistance to multi-path distortion has become a key modulation format in wireless communications. However, the main drawback in OFDM is the high peak to average power ratio (PAPR). When the signal passes a power amplifier, the signal can be distorted due to nonlinear distortion of the power amplifier. In order to resolve this drawback, PAPR reduction has been extensively studied to deal with this important issue.
In this thesis, we discuss two approaches of PAPR reduction. The first approach is the phase reversal scheme. We propose two way of modification of phase reversal scheme. One is to reduce or avoid the need of side information which is the drawback of the phase reversal scheme. The other is to enhance the PAPR performance of the phase reversal scheme. We also combine these ways two of modifications of the phase reversal scheme, and we analyze the performance on PAPR and bit error rate (BER). The second approach is the tone reservation technique, we modify the technique to enhance PAPR performance, and apply it to an orthogonal frequency division multiplexing access (OFDMA) system. Finally, we simulate and analyze of our proposed techniques and compare their performance.

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