在多載波傳收系統例如正交分頻多工系統Orthogonal Frequency Division System (OFDM)中，當子載波的持續累加下可能產生一個非常大的峰均值功率比Peak-to-Average Power Ratio (PAPR)。一個非常大的峰均值功率比(PAPR)將產生出幾個確切的問題，例如在傳收系統的設計中類比數位(A/D)、數位類比(D/A)轉換器複雜度的增加與RF功率發大器效率的降低。在本篇論文中，我們提出利用互補碼鍵鏈Complementary Code Keying (CCK)的方法產生出一個碼而且使用這個碼做QPSK數位波形調變使得系統的平均功率峰值比將被限制在一個明確的標準之下。在本文中討論了互補式序列與Walsh-Hadamard碼兩種互補碼。解碼的方法也是結合這兩種編碼所得出。為了研究我們得到的編碼與解碼效率，我們使用模擬來估計在當一個被傳送的QPSK資訊序列經過一個加性白色高斯雜訊環境系統的位元錯誤率。由模擬結果得知當這兩種碼應用於QPSK的系統時，其系統的效能與理想的QPSK系統沒有明顯的差異。 In multi-carrier transmission system such as the Orthogonal Frequency Division System (OFDM) it may generate a large peak-to-average power (PAP) ratio when the consisting sub-carriers add up coherently. A large PAP ratio will generate certain problems in the design of the transmission system such as the increase of the complexity of the analog-to-digital (A/D) and digital-to-analog (D/A) converters and the reduction of the efficiency of the RF power amplifier. In this paper we study and employ the complementary code keying (CCK) scheme to generate a code set and use this code set to modulate the QPSK digital waveform so that the system’s PAP ratio will be limited below certain level. Two code sets, namely the complementary sequences and the Walsh-Hadamard code, are considered. The decoding scheme associated with each encoding set is also derived. In order to study the effectiveness of our derived encoding and decoding schemes we use simulation technique to evaluate the system bit error rate performance when a sequence of QPSK data are transmitted through an additive white Gaussian noise environment. From the simulation result it reveals that the system is working in the way as the system is designed by using either code set.
