Anti-Blockage Beam Training for Massive MIMO Millimeter Wave Systems

Due to the short wavelength of millimeter wave (mmWave) and high directional beamforming, the 60GHz massive MIMO systems are highly vulnerable to link blockage. Beam switching to unblocked direction is an effective solution to overcome blockage. To this end, a set of backup beam pairs for beam switching must be identified at initial beam training. In this work, a low complexity beam training scheme with support for backup beam identification is proposed. Considering sparsity and clustered characteristics of mmWave channels and high probability for adjacent beams to be simultaneously blocked, we propose a new criterion for the selection of backup beams based on peak beam grouping, and design two beam grouping algorithms. The detailed procedure for beam switching when a blockage occurs is also given. Simulation results show that the proposed beam training scheme achieves near-optimal performance at initial beam training stage. Furthermore, the new method for identifying backup beam pairs is more effective to improve the spectral efficiencies of systems under blockage environments.