數位式剪波器與類比式剪波器在正交分頻多工系統下之分析

Abstract

在這篇論文裡，我們提出對正交分頻多工系統中數位式剪波與類比式剪波的分析，並從方程式中分析數位式剪波與類比式剪波對傳輸訊號的影響。早先的文獻所使用的分析方法，是將剪波器的輸入訊號假設為廣義平穩，但在正交分頻多工系統中，這樣的假設是不合適的。我們證明輸入訊號須被假設為廣義週期平穩，並且在這個假設下進行分析。我們將用模擬展示在正交分頻多工系統中，傳輸訊號經過數位式剪波與類比式剪波之後的頻譜。我們可以發現傳輸訊號經過類比式剪波之後的頻譜將會比經過數位式剪波之後的頻譜來得延展許多。模擬結果也會顯示如果假設剪波器的輸入訊號為廣義平穩，那我們將會低估剪波雜訊的效應。

In this thesis, we analyze digital and analog clipping in OFDM system. We derive the equations that show how digital and analog clipping affect the average autocorrelation of the transmitted signal. Earlier analysis of the clipped signals requires the assumption that input signal of the clipper is WSS. However, this assumption is not valid in the OFDM system in practice. We show that the clipper input should adequately be assumed to be WSCS. We will derive the power spectrum of the clipper output. Numerical simulation will be given to demonstrate the transmitted spectrum of the OFDM transmitter using analog clipping spreads more widely than the one using digital clipping. It will also be shown that transmitted spectrum is underestimated if we assume the clipper input signal is WSS.