@ARTICLE {21589,
author={D. Castanheira and P. Lopes and A.  Silva and A. Gameiro},
doi={10.1109/ACCESS.2017.2762361},
journal={IEEE Access},
title={Hybrid Beamforming Designs for Massive MIMO Millimeter-Wave Heterogeneous Systems},
year={2017},
month={December},
volume={5},
number={1},
pages={21806-21817},
ISSN={2169-3536}
}