Outage constraint based robust beamforming design for non-orthogonal multiple access in 5G cellular networks

Recently, non-orthogonal multiple access (NOMA) has received considerable attention as a promising candidate for 5G systems. In this paper, a robust beamforming approach is investigated for NOMA based multiple-input single-output (MISO) downlink transmission. We consider an outage probability based robust scheme by incorporating channel uncertainties, where the total transmit power is minimized while satisfying these outage constraints at each user. Although the original problem is non-convex in terms of beamforming vectors, an intractable optimization problem is reformulated with a linear matrix inequality (LMI) form by exploiting semidefinite relaxation (SDR) technique. Finally, simulation results have been provided to validate the performance of the proposed robust design, where these results confirm that the robust scheme outperforms the non-robust scheme in terms of the rate satisfaction ratio at each user.