Study On Variable Bandwidth Enabled Spectrum Sharing For Cognitive Radios

With the rapid development of wireless communications, the fixed spectrumallocation method leads to an increasingly significant problem of low spectrumutilization, and it becomes the main factor that hinders the development of wirelesscommunication. Cognitive radio technology is a timely manner, it solves theproblem of low spectrum utilization. Spectrum sharing is the key technology ofcognitive radio, it helps cognitive users to make full use of spectrum resources,while reduce the interference on primary users. This paper makes a deep study ondynamic spectrum sharing of cognitive radio technology, the main contents are asfollows:Aiming at the problem of low cognitive user flexibility caused by fixedspectrum allocation, reconstructive cognitive user system model with variablebandwidth mechanism is proposed. In the proposed model, average user servicelevel is used to measure the flexibility of the user, while the blocking rate and calldrop rate of cognitive users is used to measure the spectrum efficiency of thesystem.The greedy algorithm based on variable bandwidth mechanism while cognitiveusers can percept ideally is proposed. In the algorithm, in order to get the bestquality of service and use the spectrum resources effectively, cognitive users adjustthe service level uninterruptedly according to the sub-channel switch of the system.After that, a Markov transfer model is created according to system model, and thenthe system performance is evaluated. Compared with the greedy algorithm whichbased on partly adjustable bandwidth, simulation results show that the newalgorithm can solve the problem of low spectrum utilization better.In order to further optimize the performance of greedy algorithm, the variablebandwidth and dynamic spectrum sharing algorithm based on Markov decisionprocess is proposed in this paper. In the algorithm, the user access and adjustmentstrategies are re-modeled, the system revenue is the constraint for user behavior,and the particle swarm iterative method is selected for solving the maximum benefitof the system, then the optimal dynamic spectrum sharing policy is obtained.Compared with the greedy algorithm, simulation results show that both the QoSstandards and system flexibility of MDP algorithm are better than greedy algorithm.