Research on Medium Access Control for Cognitive Radio Network Based on IEEE802.22

In recent years, a variety of wireless services emerged and resulted in saturation on non-licensed bands and increasingly serious situation of "spectrum crisis". But on the other hand, according to a survey result of the FCC, the spectrum utilization of authorization band is very low and there are a large number of unoccupied band for authorized users in time and space. Therefore, it can change the existing fixed spectrum allocation and make use of licensed spectrum band holes to provide wireless services to alleviate the "spectrum crisis" of non-licensed bands, then it is required to sense surrounding wireless environment for wireless nodes and access the channel adaptively, i.e., it is required a unique kind of MAC layer access control mechanism which is different from other wireless networks.Firstly, this paper introduces the research background, research status and architecture of CR, and then some of the key technologies of IEEE802.22MAC layer are described especially.Secondly, aiming at the problem that there is not any cognition modules included in NS2and unable to support multi channel selection, the model of MobileNode are extended and some new function modules are added in order to provide reliable simulation platform for the following research in this paper.Thirdly, the original innovative improved designs on access control mechanism of the IEEE802.22are demonstrated. On the aspect of access channel priority, a new classification model based on channel statistics is proposed according to the probability of principal users’ occurrence, then the priority of cognitive users access channel is corrected into three grades combined with the original system classification model based on channel quality; On the aspect of access channel competition, the DRRO scheme and AODCC scheme are improved and optimized to enhance the overall network performance. Through the simulation results using the improved NS2platform, it is proved that the performance has improved to some extent for the proposed improvement program compared with the traditional algorithm.