A Physical Layer Security Scheme For NOMA-enabled Cognitive Radio Networks

With the development of wireless communication technology,people use related products more frequently in daily life.The proliferation of intelligent communication devices and new applications has led to the explosive growth of wireless data traffic,requiring more frequency bands to accommodate,but the available spectrum resources are limited and crowded nowadays.How to solve the problem of scarcity of spectrum resources has become the focus of current research.In order to improve the utilization of limited spectrum resources,spectrum sharing techniques have been proposed to relocate existing spectrum to obtain more spectrum resources.However,the broadcast transmission characteristics of wireless channel and the superposition characteristics of the signals in the channel lead to malicious users in the network threatening the security of legitimate users.The security of networks needs to be highly concerned.At present,the traditional security technology is the upper layer encryption technology.However,with the development of technology and increase of computing power,high-complexity security keys are in danger of leakage.Therefore,physical layer security technology has been proposed to realize the confidentiality and reliability of physical layer transmission by utilizing the dynamic characteristics of the wireless transmission link,such as the randomness of the physical layer transmission medium and the time variation of the channel state.In the current research on the utilization of spectrum resources,most people study the related characteristics of cognitive radio networks and the related performance of networks using non-orthogonal multiple access technology separately.The research on cognitive radio networks based on non-orthogonal multiple access technology is lacking,especially the research on resource allocation in secondary networks is less.In addition,the research on the security of cognitive radio networks based on non-orthogonal multiple access technology from the perspective of physical layer is also scarce.Therefore,for the above problems,this paper focuses on the network model of a pair of primary users,a secondary base station and its services to multiple secondary users,and the use of non-orthogonal multiple access technology among secondary users.This paper studies resource allocation in secondary networks and how to use physical layer security technology to ensure network security when eavesdroppers exist in the network.In a word,the main research contents and innovations of this paper are summarized as follows:First,the problem of secondary network resource allocation in cognitive radio networks based on non-orthogonal multiple access technology is studied.The aim is to improve the spectrum utilization and optimize the power and other resources in the network to achieve the optimal network performance.This paper proposes a secondary user selection algorithm and a secondary user power allocation algorithm to obtain the most suitable secondary user combination and optimize the power of selected users to achieve optimal system throughput and obtain the best transmission status.Second,for the cognitive radio network scenario with eavesdroppers,the security of the secondary network and the entire network is analyzed from the perspective of the physical layer.The secrecy sum rate of users in the network are the evaluation indicators of system security.The proposed secondary network power allocation algorithm and the power allocation algorithm of the entire network respectively obtain the optimal secrecy sum rate of secondary network and the entire network,thereby ensuring the secure and reliable transmission of information.This thesis consists of 5 chapters,including 18 figures,6 tables and 70 references.