在此篇論文中，我們首先研究在正交分頻多工系統下基於導引信號分布做通道估計，考慮在通道多路徑不在取樣的整數倍所發生的效應。我們著重在頻域方面的通道估計且導引信號是以疏狀均勻分佈在頻域上面，在此篇論文當中，通道估計是利用最小平方近似及線性最小均方誤差法求得。

當我們假設通道延遲恰好在取樣脈衝響應上時，我們觀察到利用最小平方近似法結合通道脈衝響應模組可以準確的估測出通道資訊；假如取樣不在通道延遲時間點上時，通道脈衝響應模組則會產生衰退現象；亦可以使用延著頻域做多項式估測法來取代通道脈衝響應模組估測法，接著我們更近一步的去估測真實的多路徑延遲引進旋轉不變技術估計信號參數的方法，利用此方法估測通道的真實路徑延遲並提升通道脈衝響應模組法與最小均方誤差法的效能，最後我們比較修正過後的效能進一步去探討。

In this thesis, we first study the channel estimation techniques for orthogonal frequency division multiplexing systems based on pilot signals arrangement. We consider the scenario that the multipath delays are not the sampling time instants exactly. We focus on frequency-domain channel estimation, and the pilot signals arrangement is based on the comb type. The estimation of channel frequency responses can be implemented by the least-square fitting (LSF) method or the linear minimum mean square error (LMMSE) algorithm.

When we set the multipath delays at the exact sampling time instants in the channel impulse response (CIR) model, we observe that the performance of the LSF based channel estimation degrades if the actual delays are not at the sampling time instants. We can also consider the blocks of symbols across subchannels and replace the CIR model by the polynomial model, at the cost of delay on channel estimation. We further estimate the true multipath delays based on the estimation of signal parameters via rotational invariance techniques (ESPRIT). Using the estimated multipath delays by ESPRIT, we can enhance the performance of the channel estimation that is based on the CIR or LMMSE model.

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