在無線通訊中，接收端需要得到通道資訊來等化通道的效應，以減輕多路徑的干擾在頻域上使得訊號的失真。而在決定等化器參數時，需要得到通道的頻率響應，在此篇論文中，我們在正交分頻多工系統下之時域或頻域上放入一組接收器已知的引導訊號，來估測時域和頻域通道響應。 論文中將通道估測方法分為頻域和時域兩種方法。時域估測法在時域上將資料區塊之前傳送一個接收器已知振福的脈衝，接收端能藉此獲得完整的通道響應資訊以及多路徑的數量。頻域估測法在部分的子頻帶上放入已知訊號，在其他非已知訊號上的通道頻域資訊則再藉由最小平方法和線性最小均方誤差法…等方法來估得。之後再將時域和頻域通道估測方法拓展至二維，以一次估測多個時間的通道響應來達成更好且低複雜度的估測，以兩種不相同的架構來完成二維的估測及比較其好壞。最後也在當通道延遲不在取樣時間點上發生的情況上探討其效應，並且使用超取樣來補償產生的失真。

In wireless communications, receiver needs the information of the fading channel to equalize or mitigate the distortion of the received signal. We need frequency response of the channel (CFR) to determine coefficients of the equalizer. In this thesis we estimate the channel response of OFDM systems by inserting among data symbols some pilot signals that is known to the receiver. We consider both the pilot signals in time and frequency domains.
We use time-domain (TD) and frequency-domain (FD) estimations. For the TD estimation approach, we directly transmit one pulse whose amplitude is known to the receiver in time domain before every data block, and we can easily obtain the whole instant CIR and decide the path number at the receiver. For the FD estimation approaches, we insert pilots in some subcarriers (pilot subcarriers). The CFR at other sub-channels are obtained by linear interpolation. Then we propose a two-dimension method by allowing channel estimation processed after receiving several OFDM blocks, and estimate the channels jointly to obtain better performance. Finally, we study the effect of the channel delays that are not on sampling instant exactly, and use the oversampling to compensate the distortions.

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