Robust Beamforming in Downlink MIMO NOMA Networks Using Cutting-Set Method

In this letter, we investigate robust beamforming design problem in downlink multiple-input-multiple-output non-orthogonal multiple access networks considering worst-case channel uncertainties, where worst-case means the channel uncertainties among all of them provide us the worst system performance. We propose to solve the problem using cutting-set method. The proposed cutting-set method consists of alternating optimization and pessimization steps. In the optimization step, we maximize the worst-case achievable rate of a user under worst-case achievable rate constraints of other users given finite subset of channel uncertainties. In the pessimization step, we determine the worst-case channel uncertainties. It is shown through simulation results that our proposed robust design is superior to non-robust one.