Power Optimization for Energy Efficiency in Cell-Free Massive MIMO with ZF Receiver

In this paper, a pilot-contaminated uplink cell-free massive multiple-input multiple-output (mMIMO) system with zero-forcing (ZF) receiver is considered. Then this paper derives a novel lower-bound expression for uplink energy efficiency (EE), which enables us to propose a resource optimization problem to maximize the total EE. This considered power optimization scheme takes into account the quality-of-service (QoS) requirement, each user power constraint and power consumption. Specifically, the power consumption model includes circuit power, data transmission power and backhaul power. Since the proposed power control problem is non-convex, a novel path-following approximation algorithm is characterized to tackle this problem. Simulation results indicate that the proposed algorithm only needs a few iterations to converge. Moreover, compared with equal power control (EPC) scheme, our algorithm can significantly improve the total EE.