使用數位架構的正交分頻多工系統關於峰均比之研究

Abstract

傳送訊號的峰均比( peak-to-average power ratio, PAPR )在正交分頻多工系統( OFDM system )中是很重要的討論議題。這個性質通常使用類比架構的正交分頻多工系統來做分析。 為了要得到傳輸端輸出訊號的峰均比，我們通常都會對連續時間的訊號作過度取樣( oversampling )的動作。 至於，過度取樣的取樣點多寡則視所需要的PAPR值決定。 早期的研究都是使用過度取樣因子( oversampling factor )為4來估計實際上的峰均比。現在實際上所使用的正交分頻多工系統是使用不可逆的離散傅立葉轉換矩陣( IDFT matrix )和數位類比轉換器( digital-to-analog converter )來構成傳輸端。 使用離散傅立葉轉換矩陣( DFT matrix )和類比數位轉換器( analog-to-digital )來組成接收端。在這篇論文裡面，我們會使用數位架構的正交分頻多工系統來考慮傳輸端輸出訊號的峰均比問題。 模擬的結果顯示出過度取樣因子也許需要大於4來獲得比較接近連續時間的峰均比。 除此之外，也可以發現嵌置在數位類比轉換器中的傳輸濾波器，以及嵌置在類比數位轉換器中的接收濾波器都會影響峰均比、位元錯誤率( bit error rate )、以及所需的過度取樣因子。

The peak to average power ratio (PAPR) is an important issue in OFDM systems. The quantity is typically analyzed using an analog representation of the OFDM transmitter. To obtain an estimate of the PAPR of transmitter output, the continuous-time transmitted signal is usually oversampled, based on which PAPR is computed. It has been shown earlier that an oversampling factor of 4 gives a good estimate of the actual PAPR. Modern OFDM systems are invariably implemented using an inverse discrete Fourier transform and a digital-to-analog converter for the transmitter, and a discrete Fourier transform and an analog-to-digital converter for the receiver. In this thesis, we consider the PAPR of OFDM transmitter outputs using the digital framework. The simulation results show that an oversampling factor of more than 4 may be needed to obtain a good estimate of the continuous-time PAPR value. Furthermore, the transmitting filter embedded in the digital-to-analog converter and the receiving filter embedded in the analog-to-digital converter also affect PAPR, bit error rate, and the required oversampling factor.