隨著行動裝置越來越普及，網路犯罪層出不窮，網路安全遂成為一個很重要的議題。許多網路犯罪者會偽裝他人身份進行網路犯罪，例如改變網際協定地址(IP address)或者實體地址(MAC address)來偽裝其身份。本論文探討實體層(Physical layer)安全研究，即利用射頻發射器(Radio frequency transmitter)的內部元件的不完美特性，找出數位類比轉換器(Digital to analog converter)、功率放大器(Power amplifier)、振盪器(Oscillator)的硬體非線性特徵，當作無線系統中的無線電指紋(Radio fingerprinting)。除了找出射頻發射器的內部元件非線性特徵外，我們運用訊號處理方式加強整體網路安全性，利用本論文的統計模型與演算法，分析各元件對於辨識偽裝者身份的效能。

In this work, we propose a method for identifying wireless users using the physical layer. The slight imperfections of radio frequency (RF) components in transmitters are used as a radio fingerprint to identify the wireless user in communication systems. A model-based approach for identifying users based on the imperfect components of wireless transmitter, such as the digital-to-analog converter, the power amplifier and oscillator, is exploited. For the purpose of user identification, algorithms based on statistical signal processing methods are developed using nonlinearities of wireless transmitters.

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