正交分頻多工系統在快速時變通道下會產生子頻帶間干擾，它使得位元錯誤率不會因為提高訊雜比而下降。子頻帶間干擾的問題在近幾年來越來越被探討，其產生的原因有主要兩種，載波頻率偏移以及快速時變通道。在本論文中我們會針對第二種原因加以探討。
有許多在正交分頻多工系統下的子頻帶間干擾消除方法已經被提出來，現存的方法中，犧牲傳送資料量來提升效能已經是大家的共識。在此論文裡，我們改善了一個發展於正交分頻多工系統上自相消除子頻間干擾的演算法，使用非擴展方案藉以得到更好的效能。這將會使我們傳送一個符號的時間相較於其演算法更短，受到通道變化的影響會相對的減少。

Inter-subchannel interference (ICI) is an important problem for the orthogonal frequency-division multiplexing (OFDM) system in the fast time-varying channel. It limits the achievable bit-error rate (BER) at high signal-to-noise ratio (SNR). The ICI problem has caused much concern for the OFDM system. The effect of ICI may come from carrier frequency shift or the high-mobility (fast time-varying) channel.
The first one can be solved by the frequency compensation, which, however, cannot be applied to solve the ICI caused by the fast time-varying channel.
In this thesis, we focus on ICI caused by fast channel time variation. Several algorithms of ICI reduction have been proposed for the OFDM system. As pointed out in the previous research, it is necessary to reduce the throughput for ICI reduction. In this thesis, we modify an ICI self-reduction algorithm in OFDM system by using non-extended scheme to obtain the better performance. Since we do not extend the original symbol duration, the system suffers less ICI effect due to channel variation. The simulation verifies the proposed scheme can attain better performance.

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