Subarray-Based Simultaneous Beam Training for Multiuser mmWave Massive MIMO Systems

This letter proposes a simultaneous beam training (BT) scheme for multiuser millimeter-wave systems with subarray structures. To conduct parallel BT among user-groups and hierarchical BT for each user, an adaptively allocate-subarray mechanism and a radix-4 multi-resolution codebook design are investigated. With the proposed scheme, the training overhead is significantly reduced to ${4\lceil } {\log}_{ {4}} {N}_{\text {t}} {\rceil }$ for the system with ${N}_{\text{t}}$ -antenna subarrays, and the inter-user-group-interference impact on the simultaneous BT is effectively suppressed. Numerical results verify that the proposed scheme outperforms existing counterparts in Rician fading channels.