Robust Beamforming Techniques for Non-Orthogonal Multiple Access Systems with Bounded Channel Uncertainties

We propose a robust beamforming design for non-orthogonal multiple access-based multiple-input single-output downlink systems. In particular, the robust power minimization problem is studied with imperfect channel state information, where the beamformers are designed by incorporating norm-bounded channel uncertainties to provide the required quality of service at each user. This robust scheme is developed based on the worst-case performance optimization framework. In terms of beamforming vectors, the original robust design is not convex; therefore, the robust beamformers cannot be obtained directly. To circumvent this non-convex issue, the original intractable problem is reformulated into a convex problem, where the non-convex constraint is converted into a linear matrix inequality by exploiting S-Procedure. Simulation results are provided to demonstrate the effectiveness of the proposed robust design.