Secrecy Sum Rate Optimization in Nonorthogonal Multiple Access AF Relay Networks

In this paper, nonorthogonal multiple access (NOMA) technique is employed to an amplify-and-forward (AF) relay system, which consists of a source, a relay, several users, and an eavesdropper. We aim to maximize the achievable secrecy sum rate by jointly designing power allocation at the source and cooperative beamforming at the relay, under the achievable rate constraints at the weak users and the transmit power constraints at the source and the relay. The formulated optimization problem is nonconvex due to the coupled variables. We proposed to decouple the problem into two subproblems and solve power allocation and relay beamforming in an iterative manner. Simulation results demonstrate that the proposed NOMA AF network can achieve a higher achievable secrecy sum rate than the conventional orthogonal multiple access AF relay network.