A Study Of Opportunistic Spectrum Access Technology Based Cognitive Radio

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.Our studies mainly focus on dynamic spectrum access algorithm in cognitive radio system. In the first chapter, the thesis gives an introduction of definition of cognitive radio and a summary of the recent research about cognitive radio systems. In the second chapter, the current researches of cognitive wireless access algorithm related are introduced.In the third chapter, learning-based OSA approach is studied in an unslotted cognitive radio network.It allows secondary users to achieve maximal throughput.In this approach, collisions among secondary users are taken into consideration while making channel sensing decisions. Numerical results show that the learning-based approach obtains near-optimal performance in most of the scenarios.In the fourth chapter, M-CSMA-RL is studied in a TDM cognitive radio network.Primary users use TDMA/FDMA, secondary users use M-CSMA-RL. M-CSMA-RL effectively reduces the probability of packet collisions among primary and secondary users. RL maximizes a numerical reward. The results show how the M-CSMA-RL improves both primary and secondary user's throughput at various offered traffic levels and with different ratios of primary and secondary user traffic.