應用於正交分頻多工為基礎的無線區域網路系統中之載波頻率偏移估測方法

Abstract

OFDM 是一種可以達到高速資料傳輸需求的多工技術。然而由於載波頻率飄移會導致頻際干擾使得整體系統的效能惡化，所以OFDM有一個主要的缺點就是對於由於震盪器不準所引起的載波頻率飄移相當地敏感。因此，當我們要實現一個OFDM接收器時，我們必須從受污染的資料中估測並補償它。 在這篇論文中，我們考慮三種可以應用於以OFDM為基礎WLANs之估測載波頻率飄移的演算法，並討論及比較它們的性能。由於同步符元能夠估測出大部分的載波頻率飄移，在傳送資料的部分，需要的是能夠估測很準確的演算法，而不是估測大範圍的。模擬結果指出，以隔離區間的資訊做估測的演算法最能達到這種需求。

OFDM is a promising option for high data rate communication. One of the major drawbacks is its high sensitivity to carrier frequency offset due to oscillator instability because it causes intercarrier interference and destroys the overall system performance. Consequently, it needs to be estimated and compensated from the noisy data when implementing an OFDM receiver. In this thesis, we present three carrier frequency offset estimation algorithms applied to OFDM-based WLANs. Specifically, the effects of estimator are discussed and compared. Because the major carrier frequency offset can be estimated from preamble, we need high accuracy estimator, rather wide estimated range, in the data field. In AWGN and Rayleigh fading channel, computer simulation results indicate that guard interval algorithm is most suitable to meet the requirement.