儘管正交分頻多工系統(orthogonal frequency division multiplexing, OFDM)在通訊系統中為有前景的技術，然而感知無線電在多重路徑衰減通道中最佳與實用的OFDM頻譜偵測仍是重要且具挑戰性的議題。本篇論文提出OFDM訊號新穎和最佳奈曼-皮爾生(Neyman-Pearson, NP)偵測方法。欲偵測OFDM訊號，對數概似函數試驗(log-likelihood function test)設計為利用重複的循環字首(cyclic prefix, CP)之相關性，而不需要額外的領航符元(pilot symbol)。分析結果說明，接收訊號的對數概似比(log-likelihood ration test)等於對數概似函數加上能量偵測器的對數概似比，進而對奈曼-皮爾生偵測器更深入的了解。由於有許多未知參數需要解決，我們也提出實用的廣泛概似比試驗(generalized log-likelihood ratio test, GLRT)。為在多重路徑衰減通道中達到良好效能，獲得通道獨立之廣泛概似比(CI-GLRT)為重要的，我們利用相關係數的互補特性推導出與多重路徑通道功率延遲剖面獨立的相關係數估計。此外我們也利用韋伯分析(Weibull analysis)設定通道獨立之廣泛概似比的偵測門檻值。模擬證實所提出偵測器的優點。

Despite the promising technology of orthogonal frequency division multiplexing (OFDM) in communication systems, the optimal and practical spectrum sensing of OFDM signals for cognitive radio (CR) over multipath fading channels remains an important and challenging issue. This thesis presents a novel and optimal Neyman-Pearson (NP) detection scheme of OFDM signals. To detect the OFDM signal, log-likelihood (LL) function test is formulated without requiring additional pilot symbols by using the correlation characteristics of the redundancy of cyclic prefix (CP). Analytical results indicate that the LL ratio of received samples is equivalent to their LL function plus LL ratio of energy detector, subsequently allowing us to gain insights on the Neyman-Pearson detector. Since there are many unknown parameters need to be resolved, we also present a practical generalized log-likelihood ratio test (GLRT). To obtain a channel-independent GLRT (CI-GLRT), which is important for achieving a good performance over multipath fading channels, we employ the complement property of the correlation coefficient to derive an estimation of correlation coefficient independent of multipath channel profiles. Moreover, we also use Weibull analysis to set the detection threshold of CI-GLRT. Simulations confirm the advantages of the proposed detector.

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