Spectral-efficiency optimization for NOMA-based amplify-and-forward cooperative relaying systems with beamforming and power allocation

In this paper, we propose a novel spectrum-efficiency (SE) optimization scheme for amplify-and-forward (AF) cooperative relaying systems based on non-orthogonal multiple-access (NOMA). In this network, a weighted-sum-minimum mean-squared-error (WSMMSE) method is utilized to transform the original non-convex optimization problem into a tractable optimization problem. Then, the relay beamforming-matrix (BM) and the power-allocation (PA) coefficients are alternately optimized by use of the iterative beamforming method and the Lagrange-multiplier (LM) method subject to the quality-of-service requirements. Monte Carlo simulation results verify that our proposed new scheme can attain better performance than the optimal PA-NOMA technique and the conventional orthogonal multiple-access (OMA) technique.