  Integrating cell-free massive MIMO (CF-mMIMO) into satellite-unmanned aerial
vehicle (UAV) networks offers an effective solution for enhancing connectivity.
In this setup, UAVs serve as access points (APs) of a terrestrial CF-mMIMO
network extending the satellite network capabilities, thereby ensuring robust,
high-quality communication links. In this work, we propose a successive convex
approximation algorithm for maximizing the downlink energy efficiency (EE) at
the UAVs under per-UAV power budget and user quality-of-service constraints. We
derive a closed-form expression for the EE that accounts for maximum-ratio
transmission and statistical channel knowledge at the users. Simulation results
show the effectiveness of the proposed algorithm in maximizing the EE at the
UAV layer. Moreover, we observe that a few tens of UAVs transmitting with a
fine-tuned power are sufficient to empower the service of satellite networks
and significantly increase the spectral efficiency.
