Analysis And Study Of Admission Control Algorithms In Cognitive Radio Networks

Radio spectrum resources are non-renewable strategic resources shared by human beings. Onone hand, with the rapid development of wireless technology and explosive growth of itsapplications, the shortage of spectrum resources becomes increasingly prominent. On the otherhand, the fixed spectrum allocation at present has greatly constrained spectrum efficiency. Theemergence of cognitive radio technology opens up new approach to deal with shortage ofspectrum resources, make dynamic spectrum allocation possible and improve spectrum efficiency.Cognitive radio network that adopts cognitive radio technology can dynamically adjust itsworking parameters and protocols. In the process of self-adaption, network learns and the resultwill be used for optimizing decisions made in the future, with the ultimate objective to improveend-to-end performance of the network.In a cognitive radio network, when cognitive users share licensed spectrum with primaryusers in the underlay way, network may fail to satisfy access requests of all cognitive userswithout affecting smooth communication of primary users. This requires the introduction ofadmission control mechanism to determine concurrent users. As a preventive flow control,admission control can effectively prevent network congestion and guarantee service quality forusers. Different from traditional radio networks, the major challenge on admission control in thecognitive radio network lies in the constraint on interference temperature from primary usersystem. Based on admission control algorithm of traditional radio networks, this thesis putsforward two admission control algorithms applicable to cognitive radio network. The specificresearch topics are as follows:(1) Passive admission control algorithm based on removal.It is difficult for network to support all cognitive users under high load conditions. Accordingto the ways cognitive users violate constraint conditions, three different removal strategies aredevised for cognitive users. By interweaving the iteration of user transmit power with the processof removal, this algorithm prevents interference temperature of primary users from exceedingspecified threshold in the process of power iteration and significantly reduce the probability ofinterference temperature violation, hence ensure service quality of primary users.(2) Active admission control algorithm based on mergence.When a new user requests admission of network, the admissibility of the cognitive user canbe determined through the discriminant, and if admissible, its optimal transmit power can bedetermined at the same time. The active admission control algorithm can not only reject infeasible users in advance but also admit maximum number of cognitive users and make full use ofspectrum resources. What’s more, the algorithm is independent of power control algorithm andmultiple access technology adopted by the system, so it is of general as well.