Research On Spectrum Sensing Optimization And Radio Resource Management In Cognitive Radio

With the development of wireless communication technology, the existing spectrum resource has become more and more crowded. However, the test report suggests, in fact the spectrum is not fully used for existing authorized users, there is a lot of the spectrum holes. Therefore, it becomes the key to solve the existing spectrum resources problem, which is to make full use of spectrum resources and realize the spectrum sharing.Cognitive radio was invented to solve the problem of the scarcity of the radio electromagnetic spectrum, which is to improve the utilization percent of spectral resource. The cognitive user can sensing the spectrum environment around and found that spectrum holes, then access to the unused band in opportunity ways. Cognitive radio is now recognized as one of main ways to solve the contradiction of spectrum resources by academic and industry.This dissertation focus on spectrum sensing and resource allocation management in cognitive radio networks, respectively. The hybrid cognitive network structure, the performance metrics of spectrum sensing mechanism, the physical security threat, and resources allocation management are studied with theory analysis and simulation experiment. Specifically, the cooperation spectrum sensing algorithm is studied from a single network structure to a hybrid cognitive radio network (a double fusion spectrum sensing algorithm is proposed in a hybrid cognitive radio network); Then tradeoff for performance metrics in spectrum sensing mechanism is studied (the reliability and validity tradeoff for spectrum sensing); And then cooperative spectrum sensing is studied from the ideal wireless environment to security threats attack environment, defensive attack measures is presented by considering malicious users (Based on the spectrum sensing data falsification attack, the performance for cooperation detection is analyzed and proposed a scheme to eliminate the influence of attack); Finally, the resources allocation is studied by considering the imperfect spectrum sensing, the presented resource allocation strategy based on interference constraint can meet business requirements for different cognitive users.This dissertation mainly research work and contributions are as follows:1、A double information fusion based cooperative spectrum sensing algorithm in a hybrid cognitive radio networkDue to lack of information interaction between the cognitive users and the authorized users, the spectrum sensing of the cognitive users is usually carried out in low SNR environment, which is usually suffer from multipath, shadowing and hide terminal problem. Therefore, in order to obtain more accurate sensing information, cooperative spectrum sensing technology was proposed. Different from the existing research on collaboration spectrum sensing which is based on a single cognitive network structure, the existing hybrid cognitive radio network structure in the actual wireless environment is considered, a double information fusion cooperative spectrum sensing algorithm is put forward. The proposed algorithm implements the equal gain combining and hard combining for cognitive users and cognitive base stations, respectively. From the theoretical analysis, the collaborative detection performance of the proposed scheme is derived. And then the target of the presented scheme is to maximize the detection probability with the constraint condition of false-alarm probability, and find the best number of cognitive users and cognitive base stations for cooperative spectrum sensing. Finally, the simulation results verify the feasibility of the scheme. The simulation results show that, compared with the traditional cooperative sensing scheme, the scheme still can obtain more accurate detection performance in low SNR environments. Through optimizing the number of nodes for the collaborative spectrum detection, sensing overhead and the computational complexity of the algorithm can be reduced.2、Data transmission time and interference tradeoff in spectrum sensing mechanismThe reasonable and effective spectrum detection mechanism is one of the factors to impact the utilization efficiency and the detection performance of spectrum. Therefore, for the spectrum sensing mechanism, the research on tradeoff between the validity and reliability of the spectrum sensing is necessary. Different from the existing research on sensing time and throughput tradeoff, the data transmission time and interference tradeoff for the spectrum sening is studied. The proposed scheme deduced the interference probability from the different conditions; it also considers the business of cognitive users. From the point of view of protecting the authorized user, the QoS of cognitive users is guaranteed, which meets communication demand of cognitive user, the purpose of the proposed scheme is to minimize the interference to the authorized users. Finally, the simulation results verify the reliability and rationality of the presented scheme. The simulation results show that the proposed scheme can guarantee the QoS of cognitive users, and reduces the interference to the primary user to some extent.3、Eliminate malicious users based spectrum sensing data falsification defense attack strategyOwing to the physical security threat of cognitive radio network, the spectrum sensing data falsification attack influences the performance of cooperative spectrum sensing. For the ideal wireless environment, reliability-based cooperative spectrum sensing is put forward, which considers the cognitive users in different signal-to-noise ratio environment. Compared with the traditional cooperative detection algorithm, the presented scheme can obtain the higher detection performance. Then based on the spectrum sensing data falsification attack, the impact on the cooperative spectrum sensing performance from malicious users in different situations are analyzed and derived. Finally, a reputation-based defense attack strategy with impact mitigation is put forward, malicious users with lower reputation are eliminated by calculating and updating reputation constantly. Therefore, the other trusted users participate in cooperative sensing and avoid the impact from malicious users. The simulation results show that the proposed defense against strategy not only can reduce the calculation complexity of the algorithm, but also improve the accuracy of cooperative spectrum sensing.4、An interference-based resource allocation mechanism by considering imperfect spectrum sensingUsually, existing resources allocation scheme is based on the assumption that the cognitive users achieve the accurate information of free spectrum resource, but ignores the impact from imperfect spectrum sensing to the resource allocation. In addition, most of the resource allocation schemes didn’t consider different types of service for the cognitive users; they usually assume that the cognitive users have the same resource demand. Therefore, based on the above analysis, the research is based on the interference constraints, the imperfect spectrum sensing and different business requirements from the cognitive users are jointly considered for the proposed resource allocation strategy. The target is to ensure that every user can satisfy certain communication requirements, make full use of limited spectrum resources. The goal is to maximize the channel capacity of cognitive user by considering the constraints such as interference power and quality of service guarantee. Then, by considering imperfect spectrum sensing of cognitive users, spectrum sensing of cognitive users is taken into account for constraint conditions. Based on the experimental methods, the simulation results show that the proposed resources allocation scheme both could obtain higher system capacity, also can give consideration to the different needs of cognitive users.In summary, the target of this dissertation is to improve the spectrum utilization efficiency in cognitive radio networks, the optimization of cooperative spectrum sensing, the physical security, tradeoff for sensing performance metrics, the key problems of the resources allocation are studied in detail. By modeling and analyzing of spectrum sensing and resource allocation in cognitive radio networks, corresponding solutions are put forward, and the performance is verified through the simulation results. Based on the above solutions, the cognitive users can achieve the spectrum sensing and complete spectrum allocation effectively in different network environment. The research of this dissertation provides a basis for the different business requirements in the hybrid cognitive radio network and plays a positive role for the development research and practical application of cognitive radio.