Calibrated Beam Training for Millimeter-Wave Massive MIMO Systems

Due to the inherent high path-loss of millimeterwave signals, beamforming combined with massive MIMO is crucial for increasing coverage range, whereby beam alignment via beam training is necessary to select appropriate beamforming/combining vectors at both base station (BS) and user equipment (UE) in order to acquire sufficient beamforming gain. To reduce the beam training overhead and keep the good beam alignment for millimeter-wave systems, a calibrated beam training is proposed in this paper. Firstly, BS provides a wide beam for coarse beam training and UE calculates the wide beam index by checking the received power levels. Secondly, UE refines the beam training by calculating the narrow beam index based on the ratio of beamforming gain between the selected wide beam and its neighboring wide beams. Simulation results demonstrate that the proposed scheme achieves almost the same beamforming gain as the optimal exhaustive search scheme with much reduced beam training overhead.