多載波分碼多重存取系統中雙極展頻碼及多相展頻碼之頻譜旁波特性

Abstract

此篇論文討論在多載波分碼多重存取 (Multi-carrier code division multiple access, MC-CDMA) 系統之中，傳送信號的頻譜旁波性質和頻域展頻碼的關係。其中，如果頻域展頻碼保證任意時間點之傳送信號皆保持至 階微分的連續性，則可以確保頻譜旁波隨著 的速率衰減，其中 是一個和頻域展頻碼相關的非負整數參數。在雙極展頻碼中，正交可變展頻因子碼 (Orthogonal variable spreading factor, OVSF code) 以及正交互補格雷碼 (Orthogonal complementary Golay, OCG code) 造成傳送信號頻譜旁波衰減速率可以完全由其碼字引數來表示。同樣地，在多相展頻碼中，離散傅立葉轉換碼 (Discrete Fourier transform, DFT code) 以及扎德奧夫-朱碼 (Zadoff-Chu code) 亦可以使用其碼字引數來描述對應的傳送信號頻譜旁波衰減速率。因此，藉由這些描述，可以建立具有抑制頻譜旁波的碼字揀選機制。

In this thesis, the relationship between spectral sidelobes property of transmitting MC-CDMA signal and employed spreading code is investigated. Precisely, if the spreading codeword makes transmitting signal have continuous derivatives up to -th order all the time, the corresponding spectral sidelobes decay asymptotically as , where is a nonnegative parameter related to spreading codeword. For bipolar spreading code, the spectral sidelobe decaying behavior resulting from OVSF and OCG spreading code can be described by their codeword index. Similarly, for polyphase spreading code, the spectral sidelobe decaying behavior resulting from DFT and Zadoff-Chu spreading code can be described by their codeword index, too. Accordingly, with these descriptions, it can establish sidelobes suppression scheme during codeword assignment.