  This paper considers cell-free and user-centric approaches for coverage
improvement in wireless cellular systems operating at millimeter wave
frequencies, and proposes downlink power control algorithms aimed at maximizing
the global energy efficiency. To tackle the non-convexity of the problems, an
interaction between sequential and alternating optimization is considered. The
use of hybrid analog/digital beamformers is also taken into account. The
numerical results show the benefits obtained from the power control algorithm,
as well as that the user-centric approach generally outperforms the cell-free
one.
