| With rapidly increasing of wireless communications service, fixed spectrum allocationscheme cannot meet the demand of spectrum resource. Dynamic spectrum access schemeis one of the effective methods to solve the status of lack of spectrum resources and lowutilization of spectrum resources. Cognitive radio is an emerging technology that will beproposed to improve the utilization efficiency of wireless spectrum resources. In cognitiveradio networks, secondary user can share the same frequency spectrum with primary user,when primary user is provided with enough protection.Cooperative technology can effectively enhance the accuracy of spectrum sensing andthereliabilityofdatatransmission,andcooperativecommunicationcanreduceenergydissi-pation of cognitive radio networks. Therefore, the performance optimization of cooperativetechnology of cognitive radio networks has being deeply researched, the main contributionsand results of this dissertation are as follows.(1)The performance optimization of cooperative spectrum sensing is investi-gated, and the joint optimization scheme of spectrum sensing and data transmit isproposed to minimize the outage probability of cognitive relay networks. Firstly, thebasic principle and performance of cooperative spectrum sensing are analyzed. Secondly,the improved relay cooperative transmission scheme is applied to cognitive radio network-s.Finally, the sensing time and fusion rule threshold are optimally designed to minimizedoutage probability, and the approximate expression of outage probability is given.In ad-dition, mathematical analysis and simulation results demonstrate that there exists optimalsensing time and optimal fusion rule threshold to minimize outage probability of cognitiveradio networks. The outage performance and capacity of improved scheme outperform thatof traditional transmission scheme. Furthermore，cooperative spectrum sensing can signif-icantly enhance the outage performance of cognitive relay networks.(2)Based on multi-node relay transmission model, three optimization methodsare proposed. They are optimal power allocation optimization method, optimizationmethod of optimal relay location and the joint optimization method based on ellipsemodel.Firstly, Optimal power allocation approach is presented based on known channelparameters under the constraint of total transmit power, and the optimum solution of pow- er allocation between the source and relays is given. Simulation results show the outageperformance of optimal power allocation is superior to that of equal power allocation. Sec-ondly, the optimal relay position of multi-node relay networks is analyzed based on equalpower allocation scheme. Numerical results prove that optimal relay position can optimizethe throughput and outage performance of multi-node relay networks. The farther distancebetween relay position and optimal relay location, the worse the performance of multi-noderelay networks. Finally,based on ellipse model, relay location and power allocation ratio arejointly designed to optimize capacity and outage performance of multi-node relay networks.(3)Based on cognitive multi-node relay networks, the optimization method isproposed by jointly considering spectrum sensing and power allocation. Simulationresults and optimized design of cognitive multi-node relay networks are given under theconstraint of total transmit power of cognitive source and cognitive relays, the constraintof maximum of average transmit power of secondary users and the constraint of averageinterferencepowerofprimaryuser. Simulationresultsillustratetheeffectofoptimalsensingtime, optimized power allocation, optimal relay location, the number of cognitive relay andcooperative sensing on the performance of cognitive multi-node relay networks.(4)The throughput and the energy efficiency optimization of cognitive network-s is researched based on cognitive relay model. The energy efficiency module isset up, and the optimization method of energy efficiency for cognitive radio net-works is proposed. The throughput and the energy efficiency of cognitive relay networksis researched based on equal power allocation scheme with the constraint of total transmitpower. The effect of sensing time, signal to noise ratio(SNR) and k out of M fusion ruleon the throughput and energy efficiency of cognitive networks is deeply analyzed. Numer-ical results show that there exists optimal sensing time, optimal SNR, optimal fusion rulethresholdk andoptimalnumber M ofcooperativesensinguserstooptimizedtheenergyeffi-ciency of cognitive networks. Furthermore, cooperative technology can improve the energyefficiency of cognitive radio networks. |
