Energy Efficiency Analysis and Optimization for Cell-Free mMIMO Networks

Cell-free massive multiple-input multiple-output (CF mMIMO) networks, in which multiple antennas simultaneously serve multiple user equipments (UEs), offer significant spectral efficiency (SE) gains. However, their energy efficiency (EE) performance still requires further investigation. Traditional approaches to radio resource allocation in CF mMIMO systems focus on solving the two-dimensional UE-antenna precoding problem. In this work, we propose a novel resource allocation framework that addresses the four-dimensional UE-antennafrequency-time precoding allocation for EE maximization. Considering the frequency-domain fast fading variations and timedomain traffic dynamics, we develop algorithms for EE maximization. Our heuristic delayed scheduling algorithm enhances EE by up to 10% compared to the algorithm designed for sum SE maximization. Furthermore, we demonstrate that EE performance is highly sensitive to system load, achieving a 7.4% higher EE at 69% system load compared to full load under the simulation settings. Finally, we analyze the impact of UE load on IP packet delay, establishing a relationship between the maximum UE load and packet delay budget.