超寬頻(Ultra-Wideband, UWB)通訊技術於近年來受到廣泛的注意。本論文運用統計分佈方式描述超寬頻無線傳輸通道並探討其衰落現象，且針對不同形式的脈衝無線電訊號(Impulse Radio)進行特性分析，並於系統層面架構跳時展頻技術(Time-Hopping Spread Spectrum)為超寬頻通訊之傳輸模式。由於超寬頻通道具有密集性多重路徑特性，使得耙式接收機(Rake Receiver)面臨系統效能與設計複雜度之取捨議題，因此發展出選擇性耙式接收機(Selective-Rake)之概念。其主要構想為估測接收訊號在已知無線傳輸通道所遭受之干擾強度，進而決定耙式接收機之相關器個數(Fingers)。同時以最大可能性法則(Maximum Likelihood)估測多重路徑訊號的延遲時間，結合搜尋最佳訊號路徑的CLEAN演算法，而實現選擇性耙式接收機的架構。更進一步，本論文提出改良型選擇性耙式接收機，其利用小波轉換(Wavelet Transform)的多重解析特性處理接收訊號，讓雜訊由於快速變動(Rapid Fluctuation)而造成的訊號干擾因素得以濾除。並且利用CLEAN演算法所衍生的二階段搜尋方法(Two-Stage Search)來提高最佳路徑搜尋之正確性。經由實驗結果驗證，本論文提出之改良型選擇性耙式接收機可有效提升選擇性耙式接收機的效能。

The Ultra-Wideband (UWB) communication technology has been extensively attended in recent years. In this thesis, we propose the improved selective-Rake receiver and analyze the performance on UWB channels. The UWB transmission channels are modeled with statistical methods and its fading characteristics are discussed. Different impulse radio properties for the UWB communication system are analyzed. The system performance and design complexity issues of selective-Rake receiver (SRake) are studied. Rake receiver has difficulties achieving desired system performance in the dense multipath environment. The main ideas of SRake receiver are to obtain the SNR level on known multipath channel and to determine the desired number of Rake fingers. Matched filters and maximum likelihood detectors are utilized in the implementation of the SRake to estimate the signal time delay. The CLEAN algorithm is then used in selecting the paths with relatively high energy. Furthermore, we also propose a noise cancellation scheme for performance improvement in the SRake receiver. In the noise cancellation scheme, the multiresolution property of wavelet transform is used for filtering the noise interference caused by the rapid fluctuation factor. In addition, a two-stage search is combined with the original CLEAN algorithm to increase the accuracy of path selection. From our simulation results on the UWB channels, the improved SRake receiver, with noise cancellation and two-stage search, indeed has high SRake output SNR and better path accuracy than the original SRake receiver.

第一章 導論………………………1
1.1 概觀超寬頻技術………………1
1.2 研究動機………………………5
1.3 全文結構………………………5
第二章 超寬頻傳輸通道模型……6
2.1 大區域範圍衰落特性…………7
2.2 小區域範圍衰落統計…………11
2.3 超寬頻通道分析………………15
第三章 脈衝信號波形…………………19
3.1 超寬頻系統頻寬定義………………19
3.2 單調訊號形式與特性………………19
3.3 單調訊號族群與特性………………23
3.4 系統天線對單調訊號之影響………26
3.5 脈衝無線電調變技術………………27
3.5.1 脈衝序列…………………………27
3.5.2 時間位移…………………………27
3.5.3 跳時脈波位置調變………………28
3.5.4 接收跳時脈波位置調變訊號……30
第四章 選擇性耙式接收機………………33
4.1 選擇性耙式接收機之主要概念………33
4.2 耙式接收機通用架構…………………34
4.3 選擇性耙式接收機效能分析…………38
4.4 選擇性耙式接收機之實現……………43
4.4.1 最佳多重路徑偵測器………………43
4.4.2 CLEAN演算法…………………………46
第五章 選擇性耙式接收機效能之改進方法…51
5.1 短時間傅立葉轉換…………………………51
5.2 小波轉換……………………………………54
5.3 濾波器組……………………………………57
5.3.1 分解分析…………………………………57
5.3.2 重建合成…………………………………58
5.3.3 設計濾波器組……………………………61
5.4 多重解析度…………………………………62
5.5 小波函數……………………………………66
5.6 運用小波轉換之特性濾除雜訊干擾………70
5.7 二階段搜尋方法……………………………75
第六章 改良型選擇性耙式接收機之效能分析………79
6.1 改良型選擇性耙式接收機架構……………………79
6.2 輸入訊雜比與接收機相關器個數及搜尋路徑正確性之關係………80
6.3 改良型選擇性耙式接收機之模擬結果分析………86
第七章 結論與建議………………………………………91
附錄A………………………………………………………93
附錄B………………………………………………………96
附錄C………………………………………………………98
參考文獻……………………………………………………99
中英對照……………………………………………………103

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