Research On Media Access Control Protocol For Cognitive Radio Networks

The rapid growth of the ubiquitous wireless service has imposed great pressure on the scarce and precious radio spectrum.However,the average utilization.ratio of the spectrum is not high under the current spectrum allocation system.Given this fact,a new concept of cognitive radio has been adopted to change the traditional static spectrum allocation system and to use spectrum dynamically.Cognitive radio is proposed as a way to improve spectrm efficiency by detecting the unused spectrum,changing the system operation parameters in real-time to use the free spectrum according to a certain algorithm. Therefore,it can achieve the multi-dimension spectrum utilization including time,space,frequency,which greatly reduces the limitation of spectrum and bandwidth to wireless communication technology.Hence,spectrum utilization ratio is improved.In order to achieve dynamic spectrum sharing,media access control(MAC) layer faces many difficulties that are not presented in the conventional wireless networks.Due to the advanced concepts and technology, the research of MAC protocol for cognitive radio networks remains low level And there is a lot of problems left to researchers.For example,there is no special channel for cognitive radio networks to use as a conmon control channel(CCC),and the useableness of a channel varies with activities of the primary users. And how we recover a data link from suspending,how we share radio resource in many users fairly,how to coordinate multi-channel resources,and so on.In this thesis,we have analyzed and studied the above problem in cognitive radio networks,and then a MAC protocol based on chain dynamic CCC for cognitive radio networks is proposed.A self-adapting chain dynamic CCC is created by a certain synchronous mechanism in the protocol instead of assuming a special CCC,and this is similar to a CCC in which the control information is transported in terms of cognitive users.A link restoration mechanism is proposed in the protocol to handle a sudden interruption caused by primary users.And we also have given the solutions in the protocol to hiding terminal and deaf problems.To achieve a fair sharing in free spectrum,we proposed a competition mechanism to allocate cakes.In order to achieve loading balance and avoiding multi-channel bottleneck problem,we have introduced the concept of home channel(HC) through which the pressure of control information can be shared by a group of channels,and a better network loading balance can be gained.The simulation results shows that our protocol could apply to cognitive radio networks nicely and show good performance.