Joint source power allocation and secure relay beamforming in non-orthogonal multiple access amplify-and-forward relay networks

In this paper, we investigate the joint power allocation and secure relay beamforming problem in a no-orthogonal multiple access (NOMA) amplify-and-forward relay network with two users. Our goal is to maximize the rate of the user who has better channel conditions, subject to total power constraints of the two users and a minimum signal-to-interference-ratio constraint of the user who has worse channel conditions. The formulated problem is non-convex and hard to tackle directly. To solve the problem, we firstly propose an algorithm which employing one-dimensional search to obtain the optimal solution. Since one-dimensional search may involve high computational complexity, we then propose to solve the problem with a sequential parametric convex approximation (SPCA) based iterative algorithm, which can achieve a locally optimal solution with low computational complexity. To further improve the network performance, we finally propose to solve the problem with a second-order cone programming (SOCP) based iterative algorithm. Simulation results demonstrate that the SOCP based iterative algorithm, which has lower computational complexity than one-dimensional iterative algorithm, has the performance close one-dimensional iterative algorithm. The SPCA based iterative algorithm has lowest computational complexity among proposed three methods, however, it's performance is worse.