正交頻域多工 (orthogonal frequency division multiplexing，簡稱OFDM) 系統在高資料率多載波傳輸上擁有相當多的優點，尤其在無線通訊的應用上，主要因為其在傳播通道中具有抵抗散佈的能力。而正交頻率多工在硬體實現上主要缺點之一是傳輸信號會擁有較高的尖峰平均功率比 (peak-to-average power ratio，簡稱PAPR) 。這將會造成傳輸器的平均功率下降與傳輸範圍的減少，此乃因尖峰傳輸功率受到法規或應用上的限制而有一定範圍；且較高的尖峰平均功率比會增加類比數位轉換器與數位類比轉換器的複雜度。此外，為了避免副載波間之互調變干擾與頻帶外輻射，傳輸功率放大器必須操作在線性範圍內，而較高的尖峰平均功率比需要較大的線性範圍，也就需要較昂貴的裝置，因此限制了工業上的廣泛應用。在此之前所提出來降低尖峰平均功率比的技術，可分做三類：信號失真，符號加擾，以及編碼。而編碼技術是使用一個特別的前向錯誤更正碼，使得有較大尖峰平均功率比的符號不包含在碼中而不會被傳送，先前文獻上所有為降低尖峰平均功率比使用的編碼技術，都只限於區段碼。而在本篇論文中，我們將特別著重在迴旋碼對於降低尖峰平均功率比的方法。這是由於迴旋碼擁有規則的格狀結構，可以很容易地利用斐特比演算法來解碼；此外，一般的迴旋碼早已應用在正交頻率多工系統中。最後我們並提出一個建構迴旋碼的方式來降低尖峰平均功率比。

One of the disadvantages of orthogonal frequency division
multiplexing (OFDM) systems is that OFDM signals may have high

peak-to-average power ratio (PAPR). All the previously proposed

approaches which deal with this problem employ block codes. In

this thesis, we propose terminated convolutional codes for

reduction of the PAPR. In addition, we add an offset sequence to

all the codewords so that the PAPR of the code can be decreased.

The constructed convolutional codes have low PAPR and acceptable

rate and are easy to decode by the Viterbi algorithm.

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