Statistical CSI Based Hybrid mmWave MIMO-NOMA with Max-Min Fairness

Non-orthogonal multiple access (NOMA) and millimeter wave (mmWave) transmission are two key enabling technologies for the fifth-generation (5G) mobile networks and beyond. In this paper, we consider mmWave NOMA systems with max-min fairness constraints. On the one hand, existing beamforming designs aiming at maximizing the spectral efficiency are unsuitable for the NOMA systems with fairness considered in this paper. On the other hand, previous work on mmWave NOMA mostly depends on full knowledge of channel state information (CSI) which is extremely difficult to obtain accurately in mmWave communication systems. To address this problem, we propose a heuristic hybrid beamforming design based on a statistical CSI (SCSI) user grouping strategy. An analog beamforming scheme is first proposed to mitigate inter-cluster interference in a first stage. Then two digital beamforming designs are proposed to further suppress the interference based on SCSI. One is the widely used zero forcing approach and the other is derived from the signal-to-leakage-plus-noise ratio metric extended from orthogonal multiple access systems. The effective gains fed back from the users are used for power allocation. We introduce the quadratic transform method and bisection approach to reformulate this complex problem so as to render it solvable. Simulation results show that our proposed algorithms outperform existing algorithms in term of user fairness.