摘要
認(rèn)知無線電CR（Cognitive Radio）作為一種革命性智能頻譜共享技術(shù)，以不干擾授權(quán)業(yè)務(wù)為前提，允許非授權(quán)業(yè)務(wù)利用頻段傳輸信號(hào)，可顯著提高頻譜的使用率，是解決目前頻譜資源緊張的有效手段，并逐漸成為了當(dāng)今通信界的研究熱點(diǎn)。避免干擾主用戶PU（Primary User）的正常通信是認(rèn)知無線電最重要的限制，而頻譜感知?jiǎng)t為這一目標(biāo)提供保障。為了提高頻譜感知的性能，認(rèn)知無線電網(wǎng)絡(luò)中的大量節(jié)點(diǎn)可以被用來進(jìn)行協(xié)同頻譜感知，協(xié)同頻譜感知可以有效地克服單節(jié)點(diǎn)頻譜感知的局限性。
本文首先分析研究了常用的頻譜感知技術(shù)，尤其是能量檢測技術(shù)。在無線信道中信號(hào)會(huì)受到多徑衰落、陰影的影響，將導(dǎo)致頻譜檢測性能急劇下降。為了解決這個(gè)問題，多個(gè)認(rèn)知用戶可以通過協(xié)同感知提高檢測性能。本文研究了當(dāng)今熱門協(xié)同頻譜檢測算法和協(xié)同感知中的數(shù)據(jù)融合問題，隨著參與協(xié)同檢測的認(rèn)知用戶數(shù)目的增大，頻譜檢測檢測性能逐漸增強(qiáng)。但頻譜檢測差錯(cuò)概率并不隨著認(rèn)知用戶數(shù)目的增大而繼續(xù)增大，而是趨于平緩。相反過多的認(rèn)知用戶參與協(xié)同檢測會(huì)使整個(gè)認(rèn)知無線電網(wǎng)絡(luò)的感知時(shí)間過長，即靈敏度降低。同時(shí)也會(huì)造成巨大的系統(tǒng)開銷。
本文提出了一種新的基于可信度的協(xié)同檢測算法。在滿足目標(biāo)錯(cuò)誤概率的條件下，只選擇可信度較高的一些認(rèn)知用戶參與協(xié)同頻譜檢測。仿真結(jié)果表明當(dāng)認(rèn)知用戶中存在惡意節(jié)點(diǎn)或者故障節(jié)點(diǎn)時(shí)，該算法同傳統(tǒng)算法相比較,頻譜檢測性能更好，具有更強(qiáng)的健壯性。

關(guān)鍵詞：認(rèn)知無線電；頻譜檢測；能量檢測；協(xié)同頻譜檢測





Abstract
Cognitive radio (CR) technique is considered as one of the solutions of current spectrum resource scarcity. The core idea of cognitive radio is to exploit the licensed but underutilized spectrum, in order to improve the spectrum efficiency. In cognitive radio systems, avoiding interference to primary users is the most important constraint. And spectrum sensing is the key technique to achieve this goal. In order to improve the performance of spectrum sensing, cooperative spectrum sensing is proposed, which can recover the limits of spectrum sensing by only one node.
In this dissertation, we first give an overview of some well-known spectrum sensing techniques, especially energy detection. However, in wireless channels, signals often suffer from shadowing and fading, which may lead to a very poor sensing performance. In order to solve this problem, cooperative spectrum sensing has been studied to improve the spectrum sensing performance. This dissertation focuses on the well-known cooperative spectrum sensing techniques and the optimal fusion rule for cooperative spectrum sensing. The sensing performance is improved as the number of secondary users for cooperative sensing increases. However, there exists an error floor where the decrease of the probability of error is minor and too many cooperative users will make the whole sensing time intolerantly long and huge consumption of system resource.
In this dissertation, we proposed a novel cooperative spectrum sensing algorithm. Only a few cognitive users with highest reputation are selected to cooperate while guarantees a target error bound. Numerical and simulation results show that our algorithm will be more robust and achieve better sensing performance when there exists attackers or malfunctioning cognitive users comparing with the conventional method.

Key words：cognitive radio; spectrum sensing; energy detection; cooperative pectrum sensing.




















目錄
第一章 緒論 5
1.1 研究背景及意義 5
1.1.1認(rèn)知無線電研究背景 5
1.1.2 協(xié)同頻譜感知的研究背景 6
1.2 國內(nèi)外研究現(xiàn)狀 7
1.3 主要研究內(nèi)容及論文結(jié)構(gòu) 9
第二章 頻譜感知技術(shù) 9
2.1 頻譜感知技術(shù)概述 9
2.1.1 模型定義 11
2.1.2 頻譜感知技術(shù)的性能參數(shù) 11
2.2 單節(jié)點(diǎn)的頻譜檢測技術(shù) 12
2.2.1 匹配濾波器檢測 12
2.2.2 循環(huán)平穩(wěn)特征檢測 13
2.2.3 能量檢測 14
2.3 其他檢測方法 18
2.3.1 本振泄漏檢測 18
2.3.2 基于干擾溫度限的檢測 19
2.4 本章小結(jié) 19
第三章 協(xié)作頻譜感知技術(shù) 20
3.1 協(xié)同頻譜感知系統(tǒng)的結(jié)構(gòu) 20
3.2 融合與決策規(guī)則 21
3.2.1 “與”準(zhǔn)則 22
3.2.2 “或”準(zhǔn)則 22
3.2.3 “K”秩準(zhǔn)則 22
3.3 控制信道帶寬受限條件下的協(xié)同頻譜檢測算法 23
3.3.1 基于雙門限的能量檢測算法 23
3.3.2 基于雙門限的協(xié)同頻譜檢測算法性能分析 24
3.4 基于可信度選擇認(rèn)知用戶參與協(xié)同頻譜檢測 26
3.4.1 系統(tǒng)模型 26
3.4.2 算法的實(shí)現(xiàn)步驟 28
3.4.3 仿真結(jié)果與性能分析 28
3.5 本章小結(jié) 30
第四章 總結(jié)和展望 31
參考文獻(xiàn) 33