Research On Topology Control And Optimization Method In CRN

The concept of cognitive radio technology is to develop unused spectrum in an opportunistic way.The key of cognitive radio is to effectively utilize limited spectrum through dynamic spectrum access.Cognitive radio network mainly includes two kinds of users with different priorities,namely the primary user and the secondary user.Due to the existence of the primary user(PU),the available spectrum of the secondary user(SU)has the following characteristics: spatial variability-the secondary users of different locations have different available spectrum;spectrum fragmentation-the available spectrum of secondary users is not continuous,but discrete;time variability-the available spectrum of secondary users is different with the change of time.Because of the above three factors,the topology of the cognitive radio network is constantly changing,and the dynamic cognitive radio network topology will affect the network performance.Therefore,how to maintain the stability of network topology has become a crucial problem in the research of cognitive radio network.Therefore,in view of the above problems,this paper first proposes an improved CSGC spectrum allocation algorithm to maximize the available channel time for secondary users,and then proposes a topology control algorithm based on the active behavior prediction of the primary user at the topology level.The detailed works mainly are the following.(1)First,the classification of existing topology optimization methods in cognitive radio networks,the background of cognitive radio technology,the definition of cognitive radio technology and its basic concepts are introduced.The advantages and disadvantages of existing topology optimization algorithms are summarized.(2)Then a topology control algorithm based on user activity prediction is proposed.Different with traditional wireless networks,the link state of secondary users in cognitive radio networks is affected not only by the mobility of the nodes themselves,but also by the interference of the primary users.These reasons make the topology control in mobile cognitive radio network more challenging.The problem of network topology instability is caused by the different priority between the secondary user and the primary user in the network.In this paper,a prediction model of the link available time based on the primary user activity prediction is proposed.Compared with other prediction methods,the prediction algorithm based on the activities of primary users consider the activities of the primary users,rather than simply think that as long as the secondary user entering the primary user interference radius is considered to be interference to the primary user.In this paper,the available time of the link is predicted on the basis of the above model,and the calculated link available time is used as the goal of improving the maximum spanning tree topology control algorithm.This can maximize the maintain time of network topology,avoid frequent network reconfiguration,and reduce the cost of network topology maintenance.The simulation results show that the topology control algorithm based on the activity of the primary user is more accurate for the available duration prediction of the link,and also ensures that the network topology can maintain the maximum duration.(3)Thirdly,a spectrum allocation algorithm considering channel duration is proposed.The dynamic spectrum allocation algorithm can distribute the spectrum to secondary users opportunistically.The reliability and stability of cognitive radio networks(CRN)are shown to reduce the number of channel assignments throughout the CRN by assigning the channels with high durations and high availability probabilities to secondary users as much as possible.To this end,a spectrum assignment algorithm based on graph coloring model and CRN reliability and stability is proposed in this paper.Different from existing spectrum allocation algorithms,the main idea of this paper is based on channel availability duration,which allocates the channel with high available duration to the secondary user with minimum number of interference neighbors,so that the entire spectrum allocation results can maintain a longer period of time,so as to avoid the frequent channel allocation process.The goal of this paper is to maximize duration of available channel in CRN,thereby ensuring the reliability of the entire network.Simulation results show the effectiveness and superiority of the proposed algorithm.