Study On Models And Outage Performance Of Cognitive Relay Networks

With the fast development of wireless communication, the existing allocation schemeof wireless spectrum cannot meet the growing wireless business, and the reality compels usto find new technologies to solve the problem. Spectrum sharing is the core of cognitiveradio technology, and it is able to realize the reuse of wireless spectrum resource and easethe lack of frequency bandwidth on the premise that the existing allocation scheme ofwireless spectrum need not to be changed. In this thesis, we regard the spectrum sharingmodel based on the decode-and-forward relay as the main research object, and propose twonew models in cognitive relay networks. The outage performances of primary andsecondary users have been studied, and we try to seek a tradeoff between the outageprobabilities of primary and secondary users. Based on the underlay spectrum sharing, wealso investigate the balance between primary and secondary outage probabilities and themodel where a relay cooperates both of the primary and secondary users with theconsideration of the mutual interference. The main contributions are listed as follows:For the problem of balancing the outage performances between primary andsecondary users, we analyze the signals and achievable rates in each transmission linksafter modeling the system, and obtain the theoretical results of outage probabilities.Compared with two existing communication models, the proposed model achieves betteroutage performance of primary users with the cooperation of secondary users and relay.Moreover, on the premise of guaranteeing outage performance of primary users, outageprobability of secondary users is reduced by accommodating the power allocation factor,and the purpose of balancing primary and secondary’s outage probabilities is realized.Finally, the derived results are validated by simulations.Because secondary users do not have licensed spectrum, they communicate withothers through finding free spectrum hole. Therefore, we propose the model where a relaycooperates the transmissions of primary and secondary users on the condition thatsecondary users cannot find suitable spectrum hole or the communication environment isnot ideal. Through analysis, we derive the outage probabilities of primary and secondaryusers, and the derived results are validated by simulations. Moreover, compared with anexisting model, the proposed model gets better outage performance with the cooperation ofthe relay. Meanwhile, secondary users realize the communications with each other whencommunication links are not ideal.The thesis has important implications for the improvement of primary users’ outage performance and the balance of outage probabilities, and it is significant for solving theproblem of scarce resources in wireless communications systems.