Reseach On Key Technology Of Cognitive Relay Networks

Cognitive radio(CR)is an exciting emerging technology that has the potential of dealing with the stringent requirement and scarcity of the radio spectrum.Such revolutionary and transforming technology represents a paradigm shift in the design of wireless systems,as it will allow the agile and efficient utilization of the radio spectrum by offering distributed terminals or radio cells the ability of radio sensing,self-adaptation,and dynamic spectrum sharing.Meanwhile,cooperative relay technology is regarded widely as a key technology for increasing transmission diversity gain in various types of wireless networks.Relays are able to provide the so called "virtual multiple antenna array" to make use of multi-path effect and combat fading.As a result,it can improve the reliability of wireless communications.Firstly,the cognitive radio technology is discussed.We make a discussion to different versions of its basic definitions,features,development of international standard,network architecture,key techniques and wide applications.Then the basic principles of cooperative communication are analyzed.We study the system models of multiple antenna communications and relay communications.This paper combines cognitive radio technology and cooperative communications and investigates the scenario of relay communications in spectrum sharing secondary user network.It is assumed that the communication channels are subject to independent non-identically distributed(i.n.i.d.)Nakagami-m fading.Under this channel condition,we improve the relay protocol and signal combining method in the existing literature.In this paper,a mathematical model is established for communication,in which the relay utilizes incremental decode and forward(IDF)protocol and the receiver utilizes the maximum ratio combining.For this model,the exact closed form expression is derived for outage probability and simulations are carried out to verify the correctness of the theoretical analysis.Through the analysis and simulation results,we compare the outage performances of IDF protocol and DF protocol.Besides,the influences of fading severity parameters of the relay link,direct link and interference link on the outage performance is investigated.The results show that a significant gain can be made by using IDF protocol.Moreover,the outage performance is dominated by the channel quality of the secondary transmission links and is also influenced by the channel quality of the interference links.