廣義傅利葉演算技術應用於正交分頻多工系統之效能改進

Performance Improvement of OFDM Systems Using Generalized Discrete Fourier Transform

葉育辰(Yu-Chen Yeh)

指導教授 ： 呂振森

國立臺北科技大學/電資學院/電機工程系研究所/碩士(2011年)

https://doi.org/10.6841/NTUT.2011.00352

摘要

在近期的無線通訊發展上，由於正交分頻多工調變(OFDM)技術具有高頻譜效率，使其經常被使用及研究。雖其具有高傳輸資料及許多其它的優點，但也伴隨著一些缺點，例如OFDM具有較高的均峰值功率比（PAPR），使訊號通過功率放大器時，瞬時功率高的訊號容易進入非線性區域，導致訊號失真；而另一個缺點在於其對載波頻率偏移（CFO）相當敏感，載波頻率的些許的偏差，會造成系統效能大幅減低。所以本論文針對OFDM的關鍵技術－快速傅利葉轉換，以廣義傅利葉轉換（Generalized Discrete Fourier Transform，GDFT）取代，藉由GDFT相位角非線性的特質，改變訊號波形，以改善其均峰值功率比；同時並探討改良後系統對載波頻率偏移的影響及位元錯誤率，進而研發出可使OFDM作整體改善的GDFT演算方法。

關鍵字

正交分頻多工 ； 廣義傅利葉轉換 ； 均峰值功率比 ； 載波頻率偏移

並列摘要

OFDM is a modulated technology with high bandwidth efficiency and frequently used and researched in the recent development of wireless communication. Although OFDM has high data rates and many other advantages, it still has some flaws. For example, OFDM has a higher peak-to-average power ratio（PAPR）which leads to signal distortion when the high instantaneous power input signals pass through the power amplifier and enter into the nonlinear region of the amplifier. Another drawback is the carrier frequency offset（CFO）. The OFDM system is extremely sensitive to the frequency synchronization errors. With slight CFO, the system’s performance will be significantly reduced. Therefore, this thesis will focus on the OFDM’s key technology—fast Fourier transform（FFT）. We use the generalized discrete Fourier transform (GDFT） to replace the FFT in the OFDM system. By the GDFT’s characteristic of nonlinear phases, the output signal’s waveform could be changed to reduce the PAPR. Besides PAPR, we also investigate the effect of CFO and bit error rate（BER）of these GDFT-based OFDM systems. Finally, we develop a GDFT algorithm to improve the performances of OFDM systems.

並列關鍵字

OFDM ； generalized discrete Fourier transform ； peak-to-average power ratio ； carrier frequency offset

參考文獻

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