【摘要】：無線技術(shù)由于可以靈活方便地接入通信網(wǎng)絡(luò)而備受青睞。據(jù)Erikson全球移動(dòng)公司報(bào)道,2013年手機(jī)用戶數(shù)達(dá)到了75億,這一數(shù)字已超過當(dāng)前70億的世界人口數(shù)。無線通信已成為服務(wù)技術(shù)的主流且規(guī)模正在不斷擴(kuò)大,人們不得不在公用網(wǎng)內(nèi)開發(fā)云端技術(shù)來處理大數(shù)據(jù)量的傳輸。隨著網(wǎng)絡(luò)用戶向移動(dòng)互聯(lián)網(wǎng)的轉(zhuǎn)移和物聯(lián)網(wǎng)技術(shù)的發(fā)展,無線傳輸?shù)娜萘亢涂煽啃员毁x予了更高的要求。然而如何提高頻譜利用率、采用有限的頻譜資源承載這些業(yè)務(wù)是無線通信技術(shù)進(jìn)一步發(fā)展必須要解決的首要問題。 固定的頻譜分配政策是造成頻譜利用率低下的主要原因。2003年美國(guó)聯(lián)邦通信委員會(huì)(FCC)和國(guó)際電信聯(lián)盟(ITU)等頻譜機(jī)構(gòu)發(fā)現(xiàn)各地區(qū)的頻譜利用率非常低下。為了提高認(rèn)知系統(tǒng)的頻譜使用效率和對(duì)頻譜環(huán)境的適應(yīng)能力,無線網(wǎng)絡(luò)需要具有傳感能力。1999年美國(guó)提出了通過譜傳感利用頻譜的認(rèn)知無線電標(biāo)準(zhǔn),采取動(dòng)態(tài)頻譜管理技術(shù)允許非授權(quán)用戶伺機(jī)接入授權(quán)用戶的空閑頻譜而實(shí)現(xiàn)對(duì)頻譜的有效利用。據(jù)稱該技術(shù)可以完全解決頻譜匱乏的問題,已被認(rèn)為是未來無線網(wǎng)絡(luò)的核心技術(shù)之一。 動(dòng)態(tài)利用頻譜需要解決頻譜感知和頻譜接入兩個(gè)方面的問題。前者要求系統(tǒng)對(duì)空閑頻譜實(shí)施快速而準(zhǔn)確的檢測(cè)；后者要求用戶能自適應(yīng)地接入頻譜空洞,并在發(fā)現(xiàn)主用戶的情況下快速地切換到其他信道。隱終端和無線衰落等不利的環(huán)境因素使得用戶在相互覆蓋范圍內(nèi)無法發(fā)現(xiàn)潛在的通信沖突,使得感知性能大打折扣；同時(shí)當(dāng)網(wǎng)絡(luò)負(fù)載較大時(shí),頻譜共享系統(tǒng)的服務(wù)質(zhì)量會(huì)下降。本文對(duì)這兩個(gè)方面涉及的理論與技術(shù)問題進(jìn)行深入探索,主要工作如下： 首先,介紹認(rèn)知無線電的研究背景,說明當(dāng)前頻譜危機(jī)和授權(quán)頻譜利用率低下的現(xiàn)實(shí)。然后對(duì)認(rèn)知無線電技術(shù)的概念、特點(diǎn)、各種標(biāo)準(zhǔn)、項(xiàng)目和應(yīng)用前景進(jìn)行了闡述。 第二,研究了多天線分集合并技術(shù)和頻譜感知技術(shù),并提出一種多天線的智能譜感知方法,該方法融合了匹配濾波器檢測(cè)、能量檢測(cè)和循環(huán)平穩(wěn)檢測(cè)算法。通過假設(shè)信道存在高斯噪聲和平坦Nakagami衰落而建立了相關(guān)的二元假設(shè)檢驗(yàn)?zāi)Ｐ?并推導(dǎo)出瞬時(shí)檢測(cè)概率的封閉表達(dá)式；根據(jù)SC、EGC、MRC三種多天線合并方式下的幅度增益的隨機(jī)統(tǒng)計(jì)特性,分別解析了瞬時(shí)信噪比對(duì)應(yīng)的概率分布。通過將瞬時(shí)檢測(cè)概率在其概率密度函數(shù)上進(jìn)行平均而導(dǎo)出精確的或近似的平均檢測(cè)概率表達(dá)式,同時(shí)根據(jù)各檢測(cè)算法的事件概率計(jì)算出平均檢測(cè)時(shí)間的表達(dá)式。其后利用MATLAB的數(shù)值計(jì)算工具分析了檢測(cè)概率和檢測(cè)時(shí)間的ROC特性。 第三,研究動(dòng)態(tài)頻譜接入的協(xié)議和模型。提出了一種基于服務(wù)期損失制輪詢調(diào)度的有中心混合頻譜接入方案,次用戶根據(jù)感知結(jié)果和干擾溫度判斷主用戶的活動(dòng)狀態(tài),并概率式地接入信道。通過構(gòu)建Nakagami信道下的MAC層排隊(duì)模型,解析了次用戶的平均服務(wù)率的封閉表達(dá)式。為了保證主用戶的服務(wù)質(zhì)量,規(guī)定主用戶具有最大容忍延時(shí),以此為約束條件分析了平均服務(wù)率的理論最大值。由于次用戶的業(yè)務(wù)類型往往多樣化,該部分又進(jìn)一步研究了次用戶系統(tǒng)具有多隊(duì)列排隊(duì)結(jié)構(gòu)的情形,考慮了兩種調(diào)度方案：第一種為概率式調(diào)度方案,采用拉格朗日乘子法得到了各個(gè)隊(duì)列的接入概率；第二種是損失制服務(wù)輪詢調(diào)度機(jī)制,在傳統(tǒng)的門限服務(wù)、限定1服務(wù)和完全／門限兩級(jí)優(yōu)先級(jí)服務(wù)三種的輪詢模型中假設(shè)有顧客離開,然后采用嵌入式Markov鏈和概率母函數(shù)的分析方法建立了與此調(diào)度方案相吻合的數(shù)學(xué)模型及其函數(shù)關(guān)系式,并精確解析出系統(tǒng)特性參數(shù)(平均排隊(duì)隊(duì)長(zhǎng)、平均循環(huán)周期、平均等待時(shí)延)的表達(dá)式。其后利用MATLAB的數(shù)值計(jì)算工具分析了以上參數(shù)的ROC特性。 第四,基于OPNET軟件,根據(jù)前節(jié)的多天線感知和輪詢頻譜接入方案設(shè)計(jì)了認(rèn)知無線電感知接入仿真平臺(tái),包含三個(gè)方面：在物理層,用Simulink搭建信號(hào)衰落、加性高斯信道、產(chǎn)生PU信號(hào)類型等過程；在MAC層,用OPNET搭建節(jié)點(diǎn)模塊、數(shù)據(jù)源產(chǎn)生模塊、隊(duì)列模塊；物理層和MAC層通過OPNET和MATLAB的聯(lián)合仿真引擎接口進(jìn)行信息交互。然后利用該實(shí)驗(yàn)平臺(tái)對(duì)設(shè)定的仿真場(chǎng)景下的頻譜利用率、平均排隊(duì)隊(duì)長(zhǎng)和平均等待時(shí)延等相關(guān)參數(shù)進(jìn)行了測(cè)試研究。
[Abstract]:Wireless technology is favored for its flexible and easy access to communication networks. According to Erikson Global Mobile, the number of mobile phone users reached 7.5 billion in 2013, which exceeds the current 7 billion world population. With the transfer of network users to the mobile Internet and the development of the Internet of Things technology, the capacity and reliability of wireless transmission have been given higher requirements. The first problem to be solved.
Fixed spectrum allocation policy is the main reason for low spectrum utilization. In 2003, the Federal Communications Commission (FCC) and the International Telecommunication Union (ITU) found that the spectrum utilization rate in various regions is very low. In 1999, the United States proposed a spectrum sensing cognitive radio standard, which allows unauthorized users to access the free spectrum of authorized users by dynamic spectrum management technology. It is said that this technology can completely solve the problem of spectrum scarcity and is considered to be the future wireless network. One of the core technologies of network.
The former requires the system to detect the idle spectrum quickly and accurately, while the latter requires the user to access the spectrum holes adaptively and switch to other channels quickly when the primary user is found. Environmental factors make it impossible for users to discover potential communication conflicts within the scope of mutual coverage, which greatly reduces the perception performance. At the same time, when the network load is large, the quality of service of spectrum sharing system will decline.
Firstly, the research background of cognitive radio is introduced, and the current spectrum crisis and the low utilization of authorized spectrum are illustrated.
Secondly, the multi-antenna diversity combining technique and spectrum sensing technique are studied, and a multi-antenna intelligent spectrum sensing method is proposed, which combines matched filter detection, energy detection and cyclostationary detection algorithm. According to the random statistical characteristics of amplitude gain of SC, EGC and MRC, the corresponding probability distribution of the instantaneous signal-to-noise ratio is analyzed. The accurate or approximate average detection probability is derived by averaging the instantaneous detection probability on its probability density function. At the same time, the expression of average detection time is calculated according to the event probability of each detection algorithm. Then the ROC characteristics of detection probability and detection time are analyzed by using MATLAB numerical calculation tool.
Thirdly, the protocol and model of dynamic spectrum access are studied. A centralized hybrid spectrum access scheme based on polling scheduling with loss of service is proposed. Secondary users judge the active state of primary users according to sensing results and interference temperature, and access the channel probabilistically. A closed expression of the average service rate of secondary users is given. In order to guarantee the quality of service of primary users, the maximum tolerant delay of primary users is specified, and the theoretical maximum of the average service rate is analyzed with this constraint. In the case of structure, two scheduling schemes are considered: the first is probabilistic scheduling scheme, and the access probabilities of each queue are obtained by using Lagrange multiplier method; the second is loss-based service polling scheduling mechanism, which is assumed in three polling models: traditional threshold service, limited one service and full/threshold two-level priority service. Then, the mathematical model and the function relation are established by using the method of embedded Markov chain and probability generating function, and the expression of the system characteristic parameters (average queue length, average cycle period, average waiting delay) is obtained accurately. The ROC characteristics of the above parameters are analyzed.
Fourthly, based on OPNET software, a cognitive radio sensing access simulation platform is designed according to the multi-antenna sensing and polling spectrum access scheme in the preceding section, which includes three aspects: in the physical layer, Simulink is used to build signal fading, additive Gaussian channel, and PU signal type; in the MAC layer, OPNET is used to build node module and data source generation. Module, queue module, physical layer and MAC layer interact with each other through the joint simulation engine interface of OPNET and MATLAB. Then the spectrum utilization, average queue length and average waiting delay in the simulation scenario are tested and studied.
【學(xué)位授予單位】：云南大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2014
【分類號(hào)】：TN925

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