Two-Stage 3D Codebook Design and Beam Training for Millimeter-Wave Massive MIMO Systems

Hybrid beamforming architecture that combines analog beamforming and digital beamforming has been widely accepted in the emerging millimeter-wave (mmWave) systems with large antenna arrays. However, the design of codebooks and beam training procedures at the analog stage is problematic in mmWave system. In this study, we propose a feasible two-stage 3D codebook design consisting of a primary codebook and an auxiliary codebook. The primary codebook generates a basic directional beam, and the number of phase shifts is quite limited in order to keep low hardware complexity. The small-size auxiliary codebook creates the finer beams that are centered on each primary beam. Furthermore, a beam search scheme designed for the two- stage codebook is proposed. We use a binary tree search method with antenna selection for the primary beam search, and a directed beam scan for the auxiliary beam search. Simulation results verify the performance advantages of our proposed codebook in beamforming gain and spectral efficiency for multi-user multiple-input multiple-output (MU-MIMO) systems. Moreover, training complexity comparisons indicate that our specially designed two-stage beam search scheme significantly outperforms other existing solutions.