  Cell-free massive multiple-input multiple-output (CF mMIMO) systems are
expected to provide faster and more robust connections to user equipments (UEs)
by cooperation of a massive number of distributed access points, and to be one
of the key technologies for beyond 5G (B5G). In B5G, energy efficiency (EE) is
one of the most important key indicators because various kinds of devices
connect to the network and communicate with each other. While previously
proposed transmit power control methods in CF mMIMO systems have aimed to
maximize spectral efficiency or total EE, we evaluate in this paper a different
approach for maximizing the minimum EE among all UEs. We show that this
algorithm can provide the optimum solution in polynomial time, and demonstrate
with simulations the improved minimum EE compared to conventional methods.
