Security Energy Efficiency Maximization for Two-Way Relay Assisted Cognitive Radio NOMA Network With Self-Interference Harvesting

The security energy efficiency (SEE) is investigated in a two way-full duplex (TW-FD) relay assisted cognitive radio non-orthogonal multiple access (CR-NOMA) networks. In order to improve system energy efficiency, the self-interference (SI) of FD can be regarded as a potential source for relay to harvest energy. Our objective is to maximize security energy efficiency of the secondary user (SU) system subject to harvested energy and the quality of service (QoS) of the users. Specifically, the multi-objective optimization problem is decomposed into three subproblems, i.e., the optimization of transmitting covariance matrix, power allocation, and power splitting ratio. The problem with optimizing transmit covariance matrix is non-convex, hence the semi-determined relaxation algorithm based on the first-order Taylor series expansion function is proposed to solve it. Besides, the multi-objective iterative algorithm (MOIA) is further proposed to achieve the joint optimal solution. The simulation results show 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.