藉由感知無線電(Cognitive Radio ; CR)技術，使用其技術偵測頻譜空洞，可讓次要使用者(Secondary user)合法使用授權頻段，這樣可以提升頻譜使用效率，避免浪費頻譜資源。
本論文提出一個使用於感知無線電估測接收訊號能量機率密度函數(Probability density function，簡稱PDF)的核密度估計(Kernel density function，簡稱KDF)方法。主要使用者(Primary user)的信號經由高斯白雜訊(AWGN)通道傳送，次要使用者的接收端透過波束成型(Beamforming)的方式接收主要使用者傳送的信號以提高感知效能，最後使用核密度估計(Kernel density estimation)方法估測出門檻值，並且與最佳門檻值進行比對，以評估其效能及驗證此方法的可行性。

Cognitive Radio (CR) technology is used to detect spectrum holes so that the unauthorized users are allowed to legally use the licensed frequency bands, which can improve spectrum efficiency and avoid wasting spectrum resources.
A method to estimate the probability density function (PDF) of the received signal energy by Kernel Density Estimation (KDE) is proposed in this thesis. The signals of the primary users are transmitted through the Additive White Gaussian ise (AWGN) channel, and the receivers of the secondary users receive these signals by Beamforming to enhance cognitive performance. Finally, the threshold value is estimated by Kernel Density Estimation (KDE) and compared with the optimal threshold so that the performance can be evaluated and the feasibility of this method can be verified.

第一章 緒論......................................1
1.1 研究背景...................................1
1.2 研究動機...................................3
1.3 研究目的...................................4
1.4 論文架構...................................5
第二章 感知無線電................................6
2.1 背景.......................................6
2.2 感知無線電系統.............................7
2.3 頻譜偵測..................................11
2.3.1 傳輸端偵測.............................12
2.3.2 能量偵測器.............................13
2.3.3 接收端操作特性.........................16
2.3.4 門檻值.................................17
第三章 多天線系統...............................18
3.1 多天線系統架構............................18
3.2 波束成型(Beamforing)......................19
第四章 模擬與分析...............................22
4.1 模擬流程..................................22
4.2 核密度估計介紹以及門檻值估測..............25
4.2.1 核密度估計.............................25
4.2.2 門檻值估測.............................28
4.3 蒙地卡羅模擬..............................30
4.4 模擬結果..................................32
第五章 結論及未來展望...........................41
5.1 結論......................................41
5.2 未來展望..................................41

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