Research Of Dynamic Spectrum Allocation In Cognitive Radio Network

In the traditional wireless communication environment, unlicensed users cannot freeuse licensed frequency band, and that has made the serious waste of spectrum resources.The low utilization ratio and deficiency of spectrum resources have restricted thedevelopment of wireless communications business. Cognitive radio technology provideseffective ways to solve the problem of low frequency resource use. The core idea ofcognitive radio is the dynamic spectrum allocation methods, and wireless users can accessopportunistic to idle communicational frequency band, without causing any interference tolicensed users, in order to improve the utilization rate of the spectrum. This paper mainlystudies the dynamic spectrum allocation algorithms in the cognitive radio network, aimingto improve the access performances of the secondary users, under the premise of notaffecting the primary users.First, in view of the current most of the study only limited in the analysis of accessproperties for cognitive users in the licensed channels, this paper first puts forward andestablished the "dynamic spectrum allocations model without priority ", which considercomprehensive the performance of the secondary users who accesses dynamic in theprimary channels and the secondary channels. By using the queuing theory, this papercalculate the performance metric of the secondary users, including the probability ofblocking, switching needed, switching successfully, dropping and throughput rate.According to the simulation results, this paper analyzes these five access performanceindicator 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 thenputs forward the model of dynamic spectrum allocation based on priority. The idea is tolet the secondary users preferred access free secondary channels, and then consider toaccess the free licensed channels if there is no free secondary channels. This paper firstcalculates approximatively the three dimensional stable state probability of the model ofdynamic spectrum allocation based on priority by using queuing theory.But then, in orderto get accurate performance indicators, this paper establishes a three dimensional markovchain, and give a menthod to solve the stable state probability of the three dimensionalmarkov chain by programming in MATLAB, and then we can get the performance indexsof the secondary user easily, according to the stable state probability. Finally, thesimulation results show that, without lowering the other performance indexs, comparedwith the model of dynamic spectrum allocation without priority, the switching probabilityof the secondary users is dramatically reduced in the model of dynamic spectrum allocation based on priority.