The Reasearch Of Spectrum Sensing And Access For Cognitive Radio Networks

With the rapid development of wireless communication systems and the increasing wireless communication demands, the scarcity of radio spectrum resources has become an outstanding problem. Cognitive radio (CR) is an intelligent wireless communication technology, which is viewed as a novel approach for improving the utilization of radio spectrum. The cognitive radio system is aware of its environment for changing its transmitter parameters, and it makes cognitive user dynamically access the licensed spectrums without negative effect to licensed bands. The technology contains spectrum sensing, dynamic spectrum access and management, spectrum etiquette and so on.The thesis mainly focuses on spectrum sensing and dynamic spectrum access of cognitive radio system. This thesis reviews the recent research process of cognitive radio, gives an introduction of definitions and key functions of cognitive radio system. Then the thesis summarizes the key technology in cognitive radio, including spectrum sensing, spectrum sharing and access and transmit-power control.Regarding the spectrum sensing technology, emphasis on the thesis is cooperative sensing technology. The thesis introduces the mainly kinds of non-cooperative detection methods, and gives the reasons for using cooperative sensing scheme. Then it proves the improved performance of cooperative detection though a simple model with two cognitive users. Next, the thesis proposes a model with space-qualified based on traditional model of cooperative sensing.In the part of dynamic spectrum access, thesis gives the introduction of dynamic spectrum access model. It proposes the more general model of cognitive users to access the licensed bands based on traditional spectrum pool model, and analyzes the general model with and without controlling channel assignment. Finally, the thesis proposes an access scheme with a buffer queue for cognitive radio system. The expressions and simulation results show that the proposed scheme can improve the performance of cognitive radio system.