  In this letter, we propose a robust beamforming design for non-orthogonal
multiple access (NOMA) based multiple-input single-output (MISO) downlink
systems. In particular, the robust power minimization problem is studied with
imperfect channel state information (CSI), 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 and 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 (LMI) by exploiting
S-Procedure. Finally, simulation results are provided to demonstrate the
effectiveness of the proposed robust design.
