臺灣博碩士論文加值系統

隨著無線通訊逐年發展、對頻譜資源需求的日益增加，突顯出無線頻譜嚴重缺少且不敷使用之情況。根據美國聯邦通訊委員會(Federal Communications Commission in the United States, FCC)所提出的研究報告顯示，問題出在大部分的頻帶於特定時間內並無充分使用，為提高頻譜的利用率，感知無線電(Cognitive Radio, CR)系統因此被提出。
如何準確及快速偵測到主要用戶(Primary User, PU)是否存在，並尋找頻譜空隙提供次級用戶(Secondary User, SU)使用，成為實現感知無線電的重要關鍵。本論文將採用不須預先瞭解接收訊號額外資訊的能量檢測(Energy Detection, ED)進行分析研究。首先利用能量最大可能性(Energy-based Maximum Likelihood)演算法，在不用直接計算出門檻值(Threshold, TH)的情況下，間接取得與最佳門檻值(Optimal Threshold)相同的系統效能。其次提出一個雙門檻值(Double Threshold, DT)方法，在犧牲些許偵測效能的情況下，減少偵測時間的方法。最後提出結合滯後門檻值(Hysteresis Threshold, HT)並進行修正的想法，在低訊雜比(Signal to Noise Ratio, SNR)的環境下，能達到相較於滯後門檻值HT更佳的偵測錯誤率(Probability of Error, Pe)。

As the fast development of modern wireless communication, the demand of larger spectrum allocation shows the serious shortage problem of the radio spectrum. According to the research of Federal Communications Commission in the United States (FCC), the problem lies in insufficient usage of the frequency band during allocation. To improve the utilization of wireless spectrum, the Cognitive Radio (CR) had been proposed currently.
The key issue of applying the Cognitive Radio successfully is how to sense exactly and quickly whether or not the Primary User (PU) exists, and looking for the spectrum holes to provide to the Secondary User (SU). In this thesis, the Energy based Detection (ED) CR is analyzed due to its simple advantage at the detection. First of all, instead of knowing the Threshold (TH) exactly, an Energy-based Maximum Likelihood Detection (EMLD) is proposed to have the same performance as the optimal threshold. Second, a Double Threshold (DT) method is promoted at the price of reducing some performance to reduce the sensing time. Final, combining the Hysteresis Threshold (HT) concept, a HT method is also proposed in this thesis. It has the lower probability of error (Pe) than the conventional Hysteresis Threshold especially under the low SNR scenarios.

第一章 導論 1
1.1 背景簡介 1
1.2 論文大綱 2
第二章 感知無線電 3
2.1 感知無線電系統架構 3
2.2 頻譜感測技術 4
2.2.1 獨立式檢測 5
2.2.2 合作式檢測 6
2.3 頻譜感測訊號模型 7
2.3.1 檢出機率與誤報機率 7
2.3.2 接收端操作特性 8
第三章 能量檢測法 9
3.1 訊號模型 9
3.2基於單門檻值之能量檢測法 12
3.2.1 固定誤報機率及固定檢出機率 12
3.2.2 最佳門檻值 14
3.3基於雙門檻值之能量檢測法 17
3.4基於滯後門檻值之能量檢測法 19
3.5 改進的滯後門檻值 22
3.6 能量分布最大可能性檢測 24
3.6.1 訊號模型 25
3.6.2 訊雜比估測 25
3.6.3 提出方法一(EMLD) 26
3.6.4 提出方法二(DTEMLD) 28
3.6.5 提出方法三(HTEMLD) 30
第四章 模擬與實測通道分析 33
4.1 電腦模擬分析 33
4.1.1 方案一 35
4.1.2 方案二 40
4.2 實測通道分析 53
第五章 結論 61
參考文獻 62

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