正交分頻多工(OFDM)技術在無線通訊傳輸上擁有許多的優點，如高頻譜使用效率，對符元間相互干擾和多重路徑衰減效應相當優異的扺抗力。因此，現在已經廣泛地應用於各種數位傳輸系統中，像是數位影像廣播系統、無線都會區域網路、IEEE 802.11a(一個高傳輸速率的無線區域網路標準)等等。然而，雖然正交分頻多工系統有著很多好處，但卻遭遇到一個相當嚴重的問題–多載波訊號存在著很高的尖峰平均功率比(PAPR)。因而，高功率放大器需要較寬廣的線性放大區來避免失真現象的發生，但如此一來，除了成本上較為昂貴外，也相當地沒有效率。在本篇論文中，提出了一個降低尖峰平均功率比的新方法–在正交分頻多工系統的時間域上，使用了一個直流均衡的八位元轉十位元的編碼。從模擬結果中可以看到，在16個子載波(sub-carrier)數及使用正交相移鍵控(QPSK)的正交分頻多工系統裡，所提出的方法可以將理論上最大的尖峰平均功率比由12dB降為7.4dB。而且，所提出的編碼系統除了複雜度較低以外，其複雜度也不會隨著正交分頻多工系統的子載波數增加而上升；而因為此編碼是使用在正交分頻多工系統的時間域上，所以也沒有資料傳輸率上的損失，只需要額外的數位/類比轉換器精準度上的稍微上升。除此之外，我們亦嘗試了不一樣的轉碼表(mapping table)，來觀察其對尖峰平均功率比所造成的影響。

High PAPR of the transmitted signal is a major drawback of OFDM communication systems. The PAPR reduces the power efficiency of the RF high power amplifier in the transmitter and caused distortion in the system. In this thesis, we propose a new PAPR reduction method, which uses a DC-balanced 8B/10B code in the time domain of OFDM system to reduce PAPR. The simulation result shows that the proposed method can reduce the peak PAPR value of a 16 subcarrier OFDM system utilizing QPSK modulation to < 7.4dB. The theoretical peak PAPR for the same system would be 12 dB. Moreover, the proposed method has very low complexity and the complexity does not increase as the number of OFDM subcarriers increases.

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