Research On Key Technologies In Cognitive Radio

Nowadays,the shortage of spectrum resource in the transmission process has drawn more and more attention.However,the present spectrum management strategy is mainly based on static allocation which cannot fully utilize the spectrum.A possible approach for the above problem is the cognitive radio technology based on software radio.Without affecting the communication of authorized users,cognitive radio technology can greatly improve the spectrum utilization by allocating the unused spectrum to users with communication requests.Therefore,it is of great importance to further study the cognitive radio technology which can effectively alleviate the shortage of spectrum resources and provide new ideas for the current spectrum management strategy.The thesis mainly studies several key technologies in cognitive radio including: spectrum sensing technology,dynamic spectrum allocation and spectrum sharing.The main works and contributions of this thesis are listed below: 1.Spectrum sensing technologyThe spectrum sensing technology is the basis and premise of cognitive radio and its performance is measured by whether or not it can effectively detect the unused spectrum and guarantee the communication quality of authorized users.The thesis studies the local spectrum sensing mathematical model and three common local spectrum sensing technologies: match filtering,energy sensing and cyclostationary sensing.Since only the detection result of a single node is used,the local spectrum sensing has its reliability of the local sensing greatly reduced when there is an obstacle between the authorized user and the local node.In order to solve the above problems,an improved algorithm based on double-threshold energy detection and cooperative spectrum sensing technology is proposed in this thesis.Simulation results show that the proposed algorithm can effectively improve the detection performance and reduce the system overhead.2.Dynamic spectrum allocation technologyLow spectrum utilization is an important reason for the shortage of spectrum resources.However the existing static spectrum management strategies cannot guarantee the spectrum resources be allocated on demand.In order to solve the shortage of spectrum resources once and for all,the spectrum utilization must be fully utilized.When there is an access request,the radio system has the reuse rate improved by timely allocating the idle spectrum based on the dynamic spectrum allocation technology.In this thesis,the multi-user spectrum allocation strategy of cognitive radio is studied based on graph theory coloring technology.Furthermore,the sensitive graph theory coloring algorithm is studied and compared with the traditional static spectrum allocation algorithm.In addition,an improved algorithm based on user satisfaction is proposed with the help of parallel graph theory coloring algorithm.Simulation results show that the proposed algorithm improves the user's satisfaction in addition to retaining the advantages of parallel graph theory coloring algorithm.The network efficiency is also improved.3.Spectrum sharing technologySpectrum sharing technology allows the cognitive users to share their spectrum with other cognitive users.The sharing strategy is determined by whether or not the authorized users are interfered.The spectrum sharing technology is designed to make as many cognitive users as possible to access the required spectrum meanwhile ensure the fairness among cognitive users.With the help of game theory,a spectrum sharing model is studied in this thesis based on the game between cognitive users.Finally,the performance of the existing algorithms are analyzed.