感知無線電(Cognitive Radio)為一個有效提升頻譜使用率的技術，且在感知無線電系統中，頻譜偵測(Spectrum Sensing)係相當重要之通訊偵測技術。由於遮蔽效應(Shadowing Effect)、通道衰減(Fading Channel)與多重路徑干擾(Multipath Fading)的問題，造成次要使用者無法準確的偵測主要使用者的存在；為了解決上述問題，合作式頻譜偵測(Cooperative Spectrum Sensing)方法因此孕育而生。在傳統合作式頻譜偵測方法中，假設次要使用者數目比較多，且若外界環境之雜訊能量不確定性時，其偵測效能也有所影響，顯示出傳統合作式頻譜偵測之缺陷。
　　本論文中，我們提出一新式雙臨界值混合式合作偵測系統，即傳統雙臨界值合作式能量偵測系統(Double Threshold Energy Detection)中加入統計相關性演算法(Statistical Covariances Algorithms)。傳統式能量偵測(Energy Detection)對於雜訊飄移(Noise Uncertainty)及低訊雜比(Signal to Noise Ratio)的環境，偵測效能非常差，當能量集中於雙臨界值中間區域時，偵測結果會影響整體偵測效能。故利用統計相關性演算法可以抵抗雜訊飄移及低訊雜比的問題。最後本論文再提出可降低系統複雜度的方法，但其缺點係偵測時間會增加。觀察模擬結果發現，在相同的誤警機率下，本論文提出的混合式偵測方法相較於傳統的能量偵測，可以達到較好的偵測效能。

Cognitive radio system has become a better way to improve the efficiency of spectrum usage. In cognitive radio, spectrum sensing plays a key role. However, the secondary users cannot detect the existence of the primary due the shadowing effect、fading channels、and multipath fading. To solve these problems, cooperative spectrum sensing has been proposed. For the conventional cooperative spectrum sensing system, when the number of the secondary users is large and environment exists noise uncertainty. The sensing performance would be loss. It shown that conventional cooperative spectrum sensing system seems not a good method.
　　In this thesis, we combine the statistical covariance algorithms to the conventional double thresholds cooperative energy detection and also proposed a method which can reduce the computation complexity for the hybrid detection. Simulation results show that, under the same false alarm probability, the proposed hybrid scheme achieves much better detection performance than conventional energy detection.

論文審定書 i
致謝 ii
中文摘要 iii
Abstract iv
圖次 vii
第一章 導論 1
1.1 研究背景 1
1.2 研究動機 3
1.3 論文架構 4
第二章 系統模型 5
2.1 感知無線電背景架構 5
2.2 傳統單一臨界值能量偵測 6
2.3 合作式雙臨界值能量偵測 7
第三章 傳統雙臨界值合作式能量偵測法 10
3.1 傳統雙臨界值能量偵測法系統架構 10
3.2 傳統雙臨界值能量偵測法效能分析 11
第四章 雙臨界值混合式之合作式頻譜偵測 14
4.1 現實環境中傳送訊號及雜訊的特性 14
4.1.1 雜訊不確定性 14
4.1.2 接收端超取樣 15
4.1.3 通道多重路徑干擾 15
4.1.4 多天線系統 16
4.2 雙臨界值混合式能量偵測 16
4.3 效能分析及臨界值設定 20
4.4 改善雙臨界值混合式偵測之計算複雜度 24
第五章 模擬結果 25
第六章 結論 32
參考文獻 33
中英對照表 37
縮寫對照表 41

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