| As an intelligent spectrum sharing technology, cognitive radio(CR) uses idle authorized spectrum by the way of “avail oneself of every opportunityâ€, achieving high reliable communication and efficient use of spectrum resources, solving the current problem to a large extent that the wireless spectrum resources are facing. As an important part of CR technology applied in the wireless networks, cognitive radio network MAC protocol contains a variety of CR key technologies. However, because of its frequency spectrum characteristics of dynamic, diversity, cognitive radio networks(CRNs) compared with traditional wireless networks is more complicated in studying of the MAC protocol, and most thought mechanism based on the traditional wireless networks can not be directly absorbed or used by it. In addition, throughout the current field of cognitive radio, the study in the MAC protocol is still in its infancy, there are many deficiencies and gaps, so the study of cognitive radio network MAC protocol with big challenges and important significance.Firstly, this paper introduces the research background and significance of CR technology, the definition of CR and the current research situation, the concept and key technology of cognitive radio networks, and then on the basis of summarizing the MAC protocol function and basic theory of the wireless network and combining with characteristics of the cognitive radio network, gives key technologies and performance index of the cognitive radio network MAC protocol, then according to the classification,detailed analysis and taking the disadvantages of currently existing cognitive radio network MAC protocol from the viewpoint of control channel, states the direction of the study in MAC protocol in the thesis.Secondly, in view of of the shortage of the cognitive radio network MAC protocol based on the static common control channel and the problem that some effective traditional wireless network protocol mechanism cannot be directly used for CRNs, the paper, on the basis of CR-MMAC protocol, introducing the synchronization mechanism, not waiting for transport mechanism and not reiterating mechanism, proposes a distributed local cognitive radio network MAC(CR-DCMAC) protocol, which has a dynamic common control channel(DCCC).This protocol decreases spending on channel resources by establishing DCCC, reduces load and conflict probability on the control channel, relatively increases the amount of CR users, which complete channel negotiation in ATIM window, improve the transmission capacity of the network by adopting not waiting for transport mechanism and not reiterating mechanism. And then, to set up the protocol simulation model is on NS2-based platform CRCN Simulator, after the simulation, it is to verify the relative superiority of the proposed protocol by analyzing the system throughput performance, spectrum utilization performance, etc.Finally, the paper studies the distributed cognitive radio network MAC protocol from two aspects that is the allocation mechanism of data channel and the fairness of retreat mechanism. From the main Effective Factors of the rate of data channel communication, the delay of communication and the rate of communication collision etc, puts forward a target channel selection mechanism of multiple attribute decision making,which comprehensively consider three factors that is channel gain, previous information of idle time and channel heat. This mechanism can effectively reduce the channel congestion probability and the workload of channel switching and has low computational complexity. By studying classical binary index retreat mechanism, puts forward improved binary retreat mechanism based on sending probability to improve the shortcomings of classical binary index retreat mechanism, this mechanism can further improve the fairness of the access and reduce the conflict probability after the access. At last, using NS2 platform to simulating and making performance analysis indicates the relative advantage of the proposed mechanism. |
