臺灣博碩士論文加值系統

為了有效地使用授權無線電頻段，且不能干擾主要用戶的使用權益，頻段感測是一個非常重要的研究議題。本論文提出一個有效的合作式頻段感測可以降低頻段感測報告數目到融合中心，還能保證極低的錯誤率。此方法中，每一個未授權無線電頻段的使用者(次級用戶)利用兩個門檻值λh 和 λo (λh > λo)來判斷授權頻段的使用狀態。如果一個次級用戶感知主要用戶使用的能量大於門檻值λh，則將其局部偵測結果設置為高可信結果。如果感知能量介於兩門檻之間，則將偵測結果設置為通道被占領，如果感知能量小於λo，則將偵測結果設置為通道空置。只要融合中心從任一次級用戶接收到高可信偵測結果，就能迅速判斷通道被主要用戶使用。否則，融合中心必須將所有接收到次級用戶的能量值融合一起，並利用融合能量值決定一個可靠的偵測結果，並將其廣播給所有的次級用戶。每一個次級用戶收到此結果後，與自己的偵測結果相比，假如結果一樣則將其名聲值增加，否則降低其名聲值。此名升值若小於預設之門檻值，則此一次級用戶再下一個偵測時間點，將不能傳輸其偵測結果到融合中心。模擬結果顯示我們所提出的方法與前人的方法相比有較佳的效能。

Spectrum sensing is a very important issue in cognitive radio networks. In this thesis, we propose an efficient cooperative spectrum sensing scheme which can not only reduce the number of sensing reports to the fusion center but also ensure a low miss detection probability. In the scheme, each unlicensed (secondary) user senses the licensed band and makes a local decision of the sensing result by two thresholds λh and λo (λh > λo). As long as the fusion center receives a high assured sensing result from a secondary user, it can immediately make a global decision that the licensed band is occupied. Otherwise, the fusion center need to receive the sensing energies from the secondary users and combines the received sensing energies to make a global decision. Then the fusion center broadcasts the final decision to all secondary users. Each secondary user compares the received sensing result with its local decision. If the global decision is equal to the local decision of a secondary user, the secondary user will increase its reputation value. Otherwise, the secondary user will decrease its reputation value. If the reputation value of a secondary user is smaller than a predetermined threshold, the secondary user cannot send its sensing result to the fusion center in next sensing slot. Simulation results show that the performance of our proposed method is better than previous work.

Chapter 1 Introduction...1
Chapter 2 System Model...6
Chapter 3 Cooperative Spectrum Sensing Scheme...10
3.1 Cooperative Spectrum Sensing for Secondary User...12
3.2 Cooperative Spectrum Sensing for the Fusion Center...13
Chapter 4 Performance Analysis...16
Chapter 5 Simulations...20
Chapter 6 Conclusions...26
References...27

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