在做無線通道的估測時，有兩個重要的議題需要被解決：通道的時變性以及多重路徑衰褪，在此研究中我們討論的環境是這兩個議題同時存在，這種環境也稱之為雙重衰褪的通道，此時通道的估計會變得相當複雜。在時變性的環境中，通道的估測需仰賴時域的通道相關性，而欲得知通道相關性則需要該環境的都卜勒擴展，這一般來說就已經是相當不容易的。另一方面，又必須考慮到多重路徑對通道模型的影響，會使得通道的估計複雜度變得相當的高。
在此研究中，我們將一個雙重衰褪的通道利用泰勒展開式分解，並提出了一個都卜勒擴展以及通道的聯合估計法。我們使用EM演算法迭代地算出通道以及都卜勒擴展，並且因為EM演算法的特性，可以降低同時做都卜勒擴展以及通道估測的難度。根據模擬的結果可以看出，此方法在通道的估測以及都卜勒擴展的估測都相當準確。

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