Spectral-energy efficiency maximization for wireless powered low-latency NOMA systems with full-duplex relaying

This paper investigates a wireless powered communication system, where a base station (BS) and relay first harvest energy from the power beacon and use it for data transmission. Using non-orthogonal multiple access (NOMA), the BS delivers the messages to two NOMA users via a full-duplex (FD) relay to realize low-latency communication. As two important metrics in fifth-generation communication systems, spectral and energy efficiency are jointly analyzed in this paper. Under quality of service (QoS) requirement of two NOMA users and power constraints at the BS and relay, beamforming and time allocation ratio are jointly optimized so as to maximize sum data rate and energy efficiency of system. The formulated problems are hard to be solved directly due to its non-concave objective and non-convex constraints. To tackle these, one-dimensional search and path-following-based algorithms are proposed, which can iteratively obtain improved objectives with convergence guaranteed. With fast convergence and insensitivity to problem size, the proposed algorithm can reach at least local optimum. Numerical results verify the advantages of the proposed algorithms and the superiority of the proposed scheme.