在無線感知系統中，次要使用者(Secondary user)要進行頻譜感測(Spectrum sensing)時，相對於以往的盲目取樣，若是可以先進行與主要使用者(Primary user)的時間同步，在感測上觀察視窗的決定可以有依據許多，因此本論文首先介紹傳統能量偵測器，進而假設主要使用者隨機存取頻帶的時間依循均勻分佈時，分析能量偵測器的效能變化，並在模擬驗證之餘提出解析解(analysis result)，為了得到近似最佳且更為實際的能量偵測器，提出基於廣泛概似比估測(Generalized likelihood ratio test, GLRT)的偵測演算法，並針對其中時間同步問題所使用的最大概似估測法(Maximum-likelihood estimation, MLE)及其延續的能量偵測器，分別提出了個別對應的解析解，本論文所提之偵測器有著相對其他著作的低複雜度，並能有效改善傳統能量偵測器於主要使用者抵達時間未知的問題上。

Timing misalignment issue should be addressed for the spectrum sensing in future cognitive radio (CR) systems, such as femtocell networks. To obtain a near-optimal and practical energy detector (ED), this work studies an energy detector based on the generalized likelihood ratio test (GLRT) principle. Maximum-likelihood (ML) estimation of the timing misalignment is proposed. The performance is analyzed. The proposed detector has a low complexity and can approach the optimal performance.

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