Low Complexity Fair User Scheduling Employing Spatial Orthogonality for MU-MIMO Systems

This paper proposes a low complexity fair user scheduling method employing semi-orthogonal user selection (SUS) for multi-user multiple-input multi-output (MU-MIMO) systems. The intent of the proposed approach is to consider the spatial orthogonality of users into fair user scheduling of the MU-MIMO system, which enhances the system capacity when compared to the traditional round robin (RR) based user scheduling. In the proposed method, the spatial orthogonality is calculated based on SUS which only requires the calculation of inner products among the channel state information (CSI). Therefore, both the improvement of the system capacity and fairness can be achieved with a reduced computational load. Moreover, in contrast to proportional fairness (PF), the proposed user scheduling does not require the heavy calculation of all possible user combinations as is required in MU-MIMO precoding, which is an effective and practical approach. The effectiveness of the proposed method is demonstrated and compared with RR and PF in terms of fairness and computational load.