| In order to solve the problem of low spectrum utilization, cognitive radio technologywas proposed and it has got a great development. However, in cognitive radio networks,there are also multi-path fading effects in the signal transmission, which seriously affectthe system’s wireless transmission speed and quality of service (QoS), so people usecooperative communication technology to solve this problem. The combination ofcognitive radio and cooperative technology is effective to solve multi-path fading effects,increase the coverage area, take advantage of spatial diversity gain, increase systemcapacity, improve service quality and system reliability. This thesis focuses on the cognitiveradio network cooperative communication problems.Firstly, this thesis introduces the concept of cognitive radio (CR) and give anoverview of the basic working principle, and reviews the proposal and the development ofcognitive radio and sumarries the development and research status of cooperativecommunication; this thesis also gives the relay communication system model, the basicprinciple of relay communications was introduced, the selection merger, consolidationswitch, the maximum ratio combining, equal gain combining were researched andanalyzed; this thesis researchs the methods of amplify-and-forward,decode-and-forward,coded cooperation; at last the advantages and challenges of cognitive radio networks relaytechnology were analyzed.Secondly, relay node selection is analysised, the concept and the implementationmethods of single relay node and multiple relay nodes selection was introduced, theperformance analysis of two selection schemes was studied deeply; because the outageprobability is the performance of different scenarios and schemes of cooperative relaycommunication,so this thesis studied the relay node selection scheme based on the outageprobability; the selection based on the location was researched, to select relay according tothe location of the the relay node can effectively improve the system performance.This thesis also studies the power allocation of the relay node, describes the convexoptimization theory and Lagrangian method; to maximize the system capacity, this thesisproposed the power allocation scheme based on the maximum system capacity using theLagrangian method, and give a comparison analysis of single power allocation (SPA)scheme and equal power allocation (EPA) scheme; also the interference of the primaryusers and cognitive users was analysised separately.Finally, this thesis combines the selection of the relay node and power allocation ofthe relay node, and proposed the algorithm for choosing relay nodes based on the location of relay nodes and the interference to primary nodes, the system model was discriped, andthe optimal solution was obtained by using Lagrangian method, the system performanceimprovement can be seen by simulation and performance analysis. |
