User grouping method for downlink beamforming in massive MIMO system

Base station (BS) can transmit directional beams towards specific users by downlink beamforming. However, the inter-beam interference can affect the achievable capacity severely. In this paper, we propose a user grouping method for downlink beamforming in massive multiple-input multiple-output (MIMO) system. Our method aims to group users according to the severity of inter-beam interference: users which won´t cause serious inter-beam interference are allocated into the identical group while users that cause serious inter-beam interference are distributed into different groups. By such method, users in identical group are served simultaneously while users in different groups are served in different time slots.Then we demonstrate that downlink beamforming using our method achieves better performance than using conventional SDM scheme by simulation.