Research On Dynamic Spectrum Access In Cognitive Radio Network

With the rapid development of wireless communication technology, wireless communication systems need more and more spectrums to meet different application, so the shortage of spectrum resources is becoming more and more serious. While the traditional static spectrum allocation strategy show that almost all of the spectrum resources are occupied. The contradiction between the shortage of spectrum resources and the growing demand for services restricts the development of wireless communication. However, contrast to the shortage of spectrum resources, the existing licensed spectrum is not fully utilized and there also exist some spectrum opportunity. Therefore, in order to fully used the existing licensed spectrum, some scholars have proposed the concept of cognitive radio (CR, Cognitive Radio). It is a new adaptive intelligent wireless communication system that can effectively improve the usage efficiency of spectrum. Among them, the spectrum access as the key technology of cognitive radio is widely researched in the academic and industry circles.The spectral prediction algorithm in opportunistic spectrum access has been widely concerned, as the development of the research about cognitive radio dynamic spectrum access technology. When dedicated control channel is difficult to obtain, the spectrum prediction algorithm that based on the partially observable markov decision process (POMDP) can significantly improve the usage efficiency of the system. Therefore, this paper focuses on this algorithm.The main research contents and results of this study are as follows:One cognitive radio dynamic spectrum access technology----spectrum access algorithm including the optimal strategy based on POMDP system, balance performance and the POMDP sub optimal strategy of computation, and multi cognitive user POMDP access algorithm, which was based on Partially observable Markov decision process (POMDP, Partially Observable Markov Decision Process) prediction. The lack of public control channel in existing spectrum prediction algorithm based on POMDP prediction algorithm cause the existing algorithm’s poor performance in application of many cognitive users. In order to solve the problem, this paper adopted a balanced mix channel selection policy by considering the POMDP forecast earnings and the collision rate among cognitive user. In addition, we tested and verified the feasibility to establish a model through theoretical analysis and simulation and analyzed the throughput of the system, the spectrum utilization rate and collision rate.Cognitive radio dynamic spectrum access technology could improve the spectrum utilization by comprehensive considering spectrum characteristics of usage characteristics and channel capacity. The application of POMDP prediction in the aspects of spectrum usage characteristics, could effectively know the spectrum occupancy situation among the authorized user. In the aspect of channel capacity, the different needs of different cognitive users could be realized can be meet by application of proper selection principle. Through adopting access strategy which considered the characteristics of spectrum usage and the channel capacity, this paper analysed the dynamic spectrum access by establishing models. Through theoretical analysis and simulation, we proved that the cognitive users could choose the optimal gains channel without exchange of information by the access strategy and at the same time the demand of the system on channel capacity could be meet.