This letter investigated a wireless-powered multiple-input single-output non-orthogonal multiple access downlink system, where an energy-constrained full-duplex (FD) information transmitter (IT) harvests energy from a dedicated energy transmitter (ET) and its loop channel, while IT transmits information to the information receivers (IRs). Given the quality-of-service requirements of the IRs and the constraint of the FD IT's transmit power, the minimal transmit power of the ET and the corresponding optimal beamforming vectors are obtained by applying the technique of semidefinite relaxation (SDR). Moreover, the tightness of the SDR is proved by showing the existence of the rank-one optimal solution. Then, suboptimal scheme based on interference-nulling in closed-form is also proposed by applying the Lagrangian duality method.

This letter investigates a secure MIMO system, in which a full-duplex receiver (Bob) assigns part of his antennas to emit jamming signals to confound the passive eavesdropper (Eve). Unlike previous antenna assignment schemes based on the idealized assumption that the self-interference (SI) can be canceled perfectly, we consider and quantify the contradicting effects of jamming signals acting as SI signals for Bob and confusing signals for Eve, and then formulate the antenna assignment optimization as an integer programming problem. By balancing the contradicting effects, we derive a closed-form solution and further reveal the general design guidelines, i.e., the feasibility and optimality conditions, for the considered system. Numerical results verify our theoretical analysis and demonstrate the superior performance of the proposed scheme.

In this letter, we investigate a design of efficient antenna allocation at the full duplex receiver (FDR) in a multi-input multi-output multi-eavesdropper (MIMOME) wiretap channel for physical layer security improvement. Specifically, we propose the allocation which are feasible for the practical scenario with self-interference (SI) taken into account, because the jamming signals from FDR not only confuse the eavesdropper but also inevitably cause SI at the FDR. Due to the nolinear and coupling of the antenna allocation optimization problem, we transform the original problem into an integer programming problem. Then, we derive the optimal solution and the corresponding beamforming matrices in closed-form by means of combining spatial alignment and null-space projection method. Furthermore, we present the feasibility condition and full-protection condition, which offer insight into principles that enable more efficient and effective use of FDR in the wiretap channel for security improvement. From the simulation results, we validate the theoretical analysis and demonstrate the outstanding performance of the proposed antennas allocation at FDR.