I. Introduction  
A. Approximating the Optimal Beamformer  
B. Decoupling the Design of the Analog and Digital Beamformers  
C. Wideband Hybrid Beamforming  
D. Impact of Phase-Only Constraint and the Number of RF Chains

III. Hybrid Beamforming Based on Averaged CSI  
B. Decoupling of Analog and Digital Beamformers  
C. Full-Dimensional (FD) MIMO in 3GPP

IV. Hybrid Beamforming with Selection  
A. Design of Analog Precoding/Combining Block  
B. Design of Selection Matrix

V. Hybrid Beamforming at mm-Wave  
A. Hybrid Beamforming Methods Exploiting Channels’ Sparsity  
B. Hybrid Beamforming in mm-Wave MU Scenarios

VI. Conclusion