正交分頻多工系統具有高的頻寬效率，且能夠對抗多重路徑衰減干擾的優
點；其主要的缺點為高的峰值對平均功率比問題。由於高的峰對平均功率比，使
得經過高功率放大器的信號，受到放大器操作點的影響而被截掉，引起失真。最
簡單消除的方法，是降低傳送到放大器信號的強度，使得放大器的操作點落在線
性區；但此作法會造成功率效益過低，不是合理解決方法。數位基頻預扭是既可
維持高功率效益且能夠有效線性化放大器。功率放大器是通訊系統裡一個重要元
件，本身固有的非線性性質。當一非常數信號經過非線性放大器時，其輸出會有
頻譜再生的現象，而造成鄰近通道的干擾。因此，線性化功率放大器降低位元錯
誤率的同時，也必須能夠抑制頻譜再生。
在本篇論文中，我們將分析在正交分頻多工與正交振幅調變系統下，使用預
扭器來補償由高功率放大器所引起的非線性失真，使之線性化。我們將使用到振
幅－相位預扭器補償無記憶的功率放大器；及以間接學習架構結合多項式模組，
藉由最小平方(LS)演算法求得預扭器的多項式係數，達到線性化的功率放大器。
最後，比較數種預扭器與功率放大器組合的效能。

The orthogonal frequency division multiplex (OFDM) system has advantages of
high bandwidth efficiency, and is able to resist the multipath fading interference; its major disadvantage is high peak to average power ratio (PAPR). The signal through power amplifier is clipped due to the operation point of power amplifier. This clipped signal results in distortion. The easiest method of counteracting the distortion is to reduce the intensity of the signal which enters power amplifier. This makes the operation point of power amplifier drop to linear region. It is not a reasonable solution because this method will reduce bandwidth efficiency largely. Digital baseband predistorter can not only maintain the high bandwidth efficiency but also
make predistorter cascaded with power amplifier be efficient linearization. Power amplifier which is intrinsic nonlinear characteristic is a important component in communication systems. When a non-constant signal is go through nonlinear power amplifier, its output signal has spectrum regrowth phenomenon, which gives rise to adjacent channel interference. Therefore, the linearization of power amplifier reduces bit error rate; at the same time, it also has to suppress spectrum regrowth. In this thesis, we will analyze the use of predistorter to compensate the nonlinear distortion caused by power amplifier in OFDM and QAM system. We will use amplitude-phase predistorter to compensate the memoryless power amplifier. We also use indirect learning architecture combined with polynomial-based model, which uses least-squares algorithm to obtain polynomial coefficients of predistorter, to achieve linearized power amplifier. Finally, we compare the performance which different
predistorters combined with different power amplifier.

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