| Summary: | For 3D beam access in massive multi-input multi-output (MIMO) systems, this paper proposes a feasible two-stage 3D codebook design and corresponding fast beam training algorithm. The complete codebook consists of a primary codebook and an auxiliary codebook—the primary codebook produces a basic directional beam using a smaller number of phase shifts to maintain lower hardware complexity. The small auxiliary codebook creates finer beams centered on each main beam. In addition, a beam search scheme for two-level codebook design is proposed. The main beam search is performed using a modified binary search algorithm based on the signal-to-noise ratio threshold; with the refined auxiliary codebook, the auxiliary beam search is completed using a basic binary search. The simulation results verify the performance advantages of our proposed codebook in terms of beamforming gain and beam access accuracy in MIMO systems. In addition, the comparison of beam training complexity shows that our specially designed two-stage beam search scheme has significant advantages over other existing solutions.
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