  In this paper, we employ a user-centric (UC) cell-free massive MIMO (CFmMIMO)
network for providing ultra reliable low latency communication (URLLC) when
traditional ground users (GUs) coexist with unmanned aerial vehicles (UAVs). We
study power control in both the downlink and the uplink when partial
zero-forcing (PZF) transmit/receive beamforming and maximum ratio
transmission/combining are utilized. We consider optimization problems where
the objective is to maximize either the users' sum URLLC rate or the minimum
user's URLLC rate. The URLLC rate function is both complicated and nonconvex
rendering the considered optimization problems nonconvex. Thus, we propose two
approximations for the complicated URLLC rate function and employ successive
convex optimization (SCO) to tackle the considered optimization problems.
Specifically, we propose the SCO with iterative concave lower bound
approximation (SCO-ICBA) and the SCO with iterative interference approximation
(SCO-IIA). We provide extensive simulations to evaluate SCO-ICBA and SCO-IIA
and compare UC CFmMIMO deployment with traditional colocated massive MIMO
(COmMIMO) systems. The obtained results reveal that employing the SCO-IIA
scheme to optimize the minimum user's rate for CFmMIMO with MRT in the
downlink, and PZF reception in the uplink can provide the best URLLC rate
performances.
