近來，正交分頻多工技術受到很大的關注，由於它高資料傳輸速率、與對抗各種不同通道的能力，像是多重路徑衰落、脈衝雜訊等。 儘管如此，正交分頻多工技術仍存在有許多問題。例如：符號間干擾(ISI)、載波間干擾(ICI)、及高的峰均值功率比，這些問題都能造成正交分頻多工技術的效能降低。為了改善這些問題，通道估測技術在正交分頻多工系統中變得相當重要及必須。為了避免符號間干擾及載波間干擾，前置循環字尾被廣泛地使用。本文提出一改良式架構，即利用擬雜訊序列代替循環字首。本文所提架構，將擬雜訊序列加入各個正交分頻多工符號字尾，來估測通道的脈衝響應。 為了提高系統效能，本文提出最小平方通道估測技術。所提出之演算法包含資料協助直接判決最小平方技術及最小平方估測器。 所提出技術可以達到很好的估測效能，及它的估測及追蹤通道變數的能力佳。所提出的方法亦非常適合用於大的都卜勒延展。最後會以模擬結果來說明所提出之通道估測技術有較好的效能。 Recently, OFDM (Orthogonal Frequency Division Multiplexing) techniques have received a great deal of interest due to its high transmission rate capability with high bandwidth efficiency, and its robustness against several types of channel, such as multipath fading, impulse noise, and so forth. There are still some problems in OFDM systems, such as inter-symbol interference (ISI), inter-carrier interference (ICI), and peak-to-average power ratio (PAPR). These problems can reduce the performance of OFDM system. In the cause of improving these problems, channel estimation in coherent OFDM system is necessary and essential. To avoid ISI and ICI, adding cyclic prefix (CP) is widely used. Here proposed a modify scheme by using a pseudo noise (PN) sequence instead of a CP. A PN sequence is inserted in the postfix of each OFDM symbol to estimate the channel impulse response (CIR). In order to enhance system performance, a least-square (LS) channel estimation technique is proposed in this thesis. The proposed algorithm includes least-square technique with decision-directed data-assistance and least-square estimator. The proposed techniques can achieve excellent estimation performance, and its good ability of estimating and tracking the channel variations. It is suitable in presence of large Doppler spreads. The simulations are given to illustrate the better performance of the proposed channel estimation techniques.