Research On CR-NOMA System Based On Two-way Relay

Non-orthogonal multiple access(NOMA)and cognitive radio(CR)technologies play an important role in improving the spectral efficiency of the system.In order to further improve the spectral efficiency of the CR-NOMA system and ensure the transmission quality of secondary users in the CR system,the full-duplex(FD)relay cooperative transmission technology is widely used.However,In the previous works,the CR-NOMA system is equipped with one-way relay,it takes a long time to complete the information exchange between multiple pairs of users,and the spectrum efficiency is low.Therefore,in the CR-NOMA system,it is very practical significance to assist the secondary user transmission by two-way relay(TWR).At the same time,considering the low energy efficiency and the impact of FD self-interference in the system,wireless energy transmission(SWIPT)technology can widely improve the energy efficiency of the system and harvest the self-interference generated by FD.In addition,due to the openness of the channel and the higher power sensitivity of the energy collector,information may be stolen during transmission.Therefore,it is particularly important to study the physical layer security of the CR-NOMA system.In this paper,a CR-NOMA network based on two-way relay is established,and the SWIPT technology is introduced for wireless energy harvesting and self-interference energy recycling.At the same time,considering the situation of potential eavesdroppers in the wireless environment,the problem of physical layer has also been studied.First,in order to solve the problem of poor transmission quality of secondary users and low energy efficiency in the CR-NOMA system,the cooperative transmission system model of CR-NOMA network based on two-way relay was constructed.The SWIPT technology is considered for wireless energy harvesting.This paper studies the problem of maximizing system energy efficiency with the constraints of users' service quality and minimum energy harvested.The problem formulated is non-convex,hence it is challenging to solve.The Lagrange dual and multi-objective iterative algorithm(MOIA)are further proposed to achieve joint optimal solution.The simulation result shows that compared with the traditional OWR,the proposed scheme not only improves the spectrum utilization rate,the energy efficiency of SUs also increases by 45%.Secondly,based on the two-way relay cooperative transmission,the FD selfinterference energy harvesting and CR-NOMA physical layer security issues are investigated.A CR-NOMA network based on FD two-way relay is constructed to collect energy from self-interference,which is generated by FD.Considering the effect of potential eavesdroppers in the actual wireless environment on the security performance of the physical layer of the system.Our objective is to maximize security energy efficiency of the secondary user(SU)system.Under the constraints of ensuring user service quality and minimum energy harvesting,the co-variance matrix and power allocation of the transmission signal are jointly optimized.The Taylor series expansion and semi-definite relaxation algorithm are proposed to transform the non-convex problem into a convex problem for solving.The simulation result shows that under the same constrains of power allocation and energy harvested,the proposed scheme of two way-full duplex self-interference harvest has significant performance gain on security energy efficiency over the self-interference cancellation.