正交分頻多工系統的多種特性，使得它適合使用在現在和未來的通訊傳輸技術中。但是頻率偏移對於正交分頻多工系統有明顯的影響。由於載波頻率間隔窄及頻譜間的重疊，使得正交分頻多工系統的正交特性易受到傳送、接收兩端震盪器不匹配及都卜勒效應所產生的載波間干擾所破壞。為了解決載波間干擾的問題，許多不同的方法被提出來，例如先估計出頻率偏移再加以補償的方法，或是時域窗化技術來降低其它較遠載波間的干擾，以及使用載波間干擾自動消除技術，其中載波間干擾自動消除技術是最易容執行的方法，但其缺點是浪費頻寬，因此利用相關性編碼的方法被提出來抑制載波間干擾被，但是此一方法僅在兩位元傳送系統中才有較好的系統效能。
在此篇研究中，我們提出了能在高階正交振幅調變下也可以利來相關性編碼來達到抑制載波間干擾的效果。在此一方法裡，主要是經過相關性編碼後所生成的實部部份的訊號和虛部部份的訊號利用對稱及共軛的方法來擺放在各載波上。為了驗証我們所提出來的方法的系統效能，我們提供了載波能量干擾能量比(CIR)、位元錯誤率(BER)及訊號的星座圖的電腦模擬結果。其結果都顯示了我們所提出來的方法在存在有頻率偏移的環境下和其它抑制載波間干擾的方法有著明顯的優勢，可以在不增加系統複雜度之下提升系統效能。

Orthogonal frequency division multiplexing (OFDM) has been widely adopted in the next generation wireless communication systems. A major disadvantage of OFDM systems is the sensitivity to the frequency offset, which is usually caused by mismatch of the oscillators between the transmitter and the receiver or the Doppler effect. The frequency offset will destroy the orthogonilty among subcarriers and then introduce intercarrier interference (ICI), which degrades the system performance dramatically. Several methods have been proposed to combat the ICI effect in the OFDM systems. One of the simple and effective methods is the ICI self-cancellation scheme, but the spectral efficiency is half of the standard OFDM system. On the other hand, ICI can be handled by performing correlative coding in frequency domain. However, such correlative coding schemes could only perform well in BPSK modulation. When higher order modulation scheme is used, the performance would be sdegraded significantly.
In this thesis, we propose a new ICI suppression scheme that can be regarded as an improved version of the correlative coding approach. The intention of our approach is to overcome the high bit error rate (BER) situation occurring in the conventional correlative coding scheme due to the severe error propagation problem when high order modulation is chosen. To achieve this goal, we transmit real and imaginary part of correlative coding signals separately. Simulation results show that the proposed scheme not only keep the immunity against ICI, but also mitigate the severe error propagation in the conventional correlative coding scheme when high order modulation is used.

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