文档介绍：Abstract
In the traditional munication environment, unlicensed users cannot free use licensed frequency band, and that has made the serious waste of spectrum resources. The low utilization ratio and deficiency of spectrum resources have restricted the development of munications business. Cognitive radio technology provides effective ways to solve the problem of low frequency resource use. The core idea of cognitive radio is the dynamic spectrum allocation methods, and wireless users can access opportunistic to municational frequency band, without causing any interference to licensed users, in order to improve the utilization rate of the spectrum. This paper mainly studies the dynamic spectrum allocation algorithms in the cognitive work, aiming to improve the access performances of the secondary users, under the premise of not affecting the primary users.
First, in view of the current most of the study only limited in the analysis of access properties for cognitive users in the licensed channels, this paper first puts forward and established the "dynamic spectrum allocations model without priority ", which prehensive the performance of the secondary users who accesses dynamic in the primary channels and the secondary channels. By using the queuing theory, this paper calculate the performance metric of the secondary users, including the probability of blocking, switching needed, switching essfully, dropping and throughput rate. According to the simulation results, this paper analyzes these five access performance indicator of the secondary users in the no priority model.
And then, considering that the frequent channels switching will bring large time delay, this paper improves the model of dynamic spectrum allocation without priority, and then puts forward the model of dynamic spectrum allocation based on priority . The idea is to let the secondary users preferred access free secondary channels, and then consider to access the free licensed channels if there is no