本論文中將EM法則應用於RAKE接收機，解決多路徑訊號傳輸所造成時間延遲與時變衰弱問題。主要概念為，以展頻系統為中心，以EM法則依照接收訊號的個別部分，分解所接收的DATA，並對訊號各部分參數分離估計。參數估測值透過最大比例結合器運用於RAKE接收機，以其提高系統之強健性，減低RAKE接收機因環境快速變化造成效能之受限。
EM(Expectation-Maximization) 法則為統計學中“最大似然估計”(ML, Maximum Likelihood) 所應用的方法，EM法則使用機率分布函數來表示影響訊號的參數(如訊號增益，雜訊增益，時間延遲)。EM法則重複使用現有參數估計，協助解析所接收DATA，因而增加下一個參數估計的精確度。在不犧牲偵測精確度下，能夠相當程度的簡化計算，分離偵測所有的未知訊號參數，提高RAKE接收機之效能。在許多研究中，證明EM法則運用於多路徑訊號參數估測，有極佳之效果。且由實驗結果證明，將EM法則應用於RAKE接收機之參數估測，確實可改善RAKE接收機之效能。

We employ the RAKE receiver with EM (expectation-maximization) algorithm to solve the problems of multipath propagation and fading. The key issue is to decompose the observed data into their channel components, then to estimate the unknown parameters of each channel separately. Using the maximal ratio combiner, the estimated parameters are applied to the RAKE receiver to improve the performance.
EM algorithm produces maximum-likelihood estimates of parameters when there is a many-to-one mapping from an underlying distribution to the distribution governing the observed data. With the property of convergence, the algorithm is iterated with increasing likelihood. As a result, the proposed RAKE receiver has a better performance than the traditional one in terms of BER.

1.1 研究動機．．．．．．．．．．．．．．．．．．．．． 1
1.2 組織大綱．．．．．．．．．．．．．．．．．．．．． 3
第二章 RAKE接收機 4
2.1 多路徑衰弱通道．．．．．．．．．．．．．．．．．． 4
2.2 多路徑衰弱通道模擬．．．．．．．．．．．．．．．． 5
2.3 數位展頻通訊系統．．．．．．．．．．．．．．．．． 7
2.4 RAKE接收機．．．．．．．．．．．．．．．．．．．．13
第三章 EM法則應用於接收機之參數估測 17
3.1 EM法則．．．．．．．．．．．．．．．．．．．．．．17
3.2 E-step與M-step．．．．．．．．．．．．．．．．．．19
3.3 多路徑訊號參數估測．．．．．．．．．．．．．．．．20
3.4 RAKE接收機之參數估測．．．．．．．．．．．．．．．26
第四章 電腦模擬與結果分析．．．．．．．．．．．．．． 30
第五章 結論與展望．．．．．．．．．．．．．．．．．． 37
參考文獻．．．．．．．．．．．．．．．．．．．．．．．38

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