  In this paper, a downlink non-orthogonal multiple access (NOMA) network is
studied. We investigate the problem of jointly optimizing user pairing and
beamforming design to maximize the minimum rate among all users. The considered
problem belongs to a difficult class of mixed-integer nonconvex optimization
programming. We first relax the binary constraints and adopt sequential convex
approximation method to solve the relaxed problem, which is guaranteed to
converge at least to a locally optimal solution. Numerical results show that
the proposed method attains higher rate fairness among users, compared with
traditional beamforming solutions, i.e., random pairing NOMA and beamforming
systems.
