在本論文中，我們主要是要探討在中低速情況且有直視成分存在下，都普勒擴展的估測。都普勒擴展是個與車速有關係的因子，因此都普勒估測對行動通訊系統是非常重要的，準確的估測會對行動通訊系統的通道估測、同步等，有相當大的幫助；然而在中低速的情況下，都普勒擴展估測的成效，會因為通道取樣之間的相關性變高而受到很大的影響。另外直視成分的存在，則會使得都普勒擴展的估測變得麻煩許多，因為直視成分包含了如入射角、初始相位偏移等其他未知的因子，這些因子也會影響到我們都普勒擴展估測的成效。
近來已有利用通道取樣的協方差來解決這類問題，主要是利用長時間通道取樣的協方差的特性，來進行在有直視成份下的都普勒擴展估測。然而在中低速的情況下，由於通道變化緩慢，使得這類作法在這種情況下，必須收集非常大量的取樣資料來進行估測，顯得有些不切實際；且當直視成份變大時，成效也會變差。在論文中，我們主要是提出以最大似然法則為基礎的估測法最大似然估測是一個大家熟知在中低速情況有不錯成效的估測法，且由於有直視成份的存在我們也會提出一套對直視成分的估測法則。在後面的模擬結果可看出，此估測法有不錯的成效，且與利用通道取樣協方差的方法相比，我們的估測法更能有效對付中低速情況和直視成分之影響。

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