Access Control Algorithm In Cognitive Radio Systems Research

With the continued development of broadband wireless communication, the scarceness of wireless spectrum resources has become a major bottleneck of the development of wireless communication systems. People advance that there's much more load depending on a small amount of frequency bands while other parts of them have fewer efficiency of utility. Cognitive radio technology is an intelligent wireless radio which is able to sense the wireless environment to identify available spectrum resources. It can access spectrum intelligently, dynamically and enhance the utilization of the spectrum resources. This rising wireless access technology is considered revolutionary wireless communications technology which can ease the problem of the lack of resources spectrum .The research of cognitive radio technology has become a hot area of wireless communications.Our studies mainly focus on dynamic spectrum access algorithm in cognitive radio system. First, the thesis gives an introduction of definition of cognitive radio and a summary of the recent research about cognitive radio systems. Then the current researches of cognitive wireless access algorithm related are introduced.Cognitive users may be in different environment which will result each user of their available spectrum is also different. In consideration of that difference among cognitive users, a dynamic access probability for multichannel random access algorithm for cognitive radio system is proposed to reduce conflicts of user access. It estimates the number of users to access channel, then dynamically changes the channel access probability to reduce conflict and improve the performance of system. Through computer simulation has demonstrated a better performance of success of system access probability and the times of retry.Then CSMA mechanism in cognitive environment is studied .We illuminate the t application of CSMA requires to make improvements to adapt to the cognitive environment. Through the establishment of the mathematical model under different parameters, the throughput of the system is given the simulation shows that different parameters on the cognitive radio systems in the mechanism of the throughput of the CSMA impact.