Physical Layer Security Research For Cooperative CR-NOMA Network

With the development of wireless communication networks,wireless multimedia services are constantly expanding,and the explosive growth of data traffic puts forward higher requirements for wireless communication networks in terms of spectrum efficiency.The popularization of massive machine communication,such as Internet of Things,aggravates the shortage of spectrum resources.Non-orthogonal Multiple Access(NOMA)and cognitive radio(CR)have a prospect of relieving the bottleneck of spectrum resources.In order to improve the reliability of simultaneous multi-user communication in the further,cooperative CR-NOMA network is widely studied.On the other hand,with the large-scale deployment of sensors and intelligent gateways in mass machine communications,the Simultaneous Wireless Information and Power Transfer(SWIPT)technology,which provides a permanent energy complement to energy-constrained low-power devices,has received widespread attention.Studies have shown that SWIPT technology supporting simultaneous information and power transmission can be used to improve the power and spectral efficiency of communication systems.For this purpose,the interrupt performance and secure transmission performance of the system are studied for cooperative CR-NOMA network,joint relay selection and SWIPT technology.The main contributions are as follows:Firstly,the basic theory of cooperative NOMA and SWIPT are introduced,and further explains the key technologies such as relay selection,forwarding protocol and successive interference cancellation.Secondly,for underlay non-orthogonal multiple access cognitive networks using SWIPT,a two-stage relay selection strategy(TSRS)based on NOMA and successive interference cancellation protocols is proposed.Under the interference temperature constraint to protect the primary user,the source node and the optimal relay of the secondary network both generate multiuser superimposed signals with a fixed power allocation for them to be sent on the next hop link.The optimal relay harvests energy from the first-hop link by using the power splitting scheme,and uses only the harvested energy to provide the decode-and-forward(DF)service.The closed-form expressions for users’ outage probabilities are derived and verified by Monte Carlo simulations.The influences of system parameters such as power allocation factor,energy splitting parameter,interference temperature constraint,and the number of relays on the outage performance is analyzed.Simulation results show that the proposed scheme can significantly improve the outage performance of the system.Finally,Considering the application of SWIPT technology in the underlay non-orthogonal multiple access and vehicle to everything(NOMA-V2X)cognitive networks,when the secondary network is interfered by the primary network,a two-stage relay selection scheme suitable for non-orthogonal multiple access networks is proposed.The secondary network source node uses fix power allocation scheme to broadcast superimposed signals to all relays,at the same time the relays are interfered by the primary network signal.The selected relay uses the power split schem e to perform SWIPT,and the power collected is only used to forward decoded signal.Under the limit of interference temperature constraint,the approximate expression of outage probability for each secondary user is derived,and the correctness of numerical analysis is verified.By analyzing the influence of system parameters on the outage probability of secondary users,it is proved that the TSRS scheme is superior to the existing scheme in improving the outage performance.