Towards Optimal Energy Efficiency in Cell-Free Massive MIMO Systems

A. Papazafeiropoulos, H. Q. Ngo, P. Kourtessis, S. Chatzinotas, J. M. Senior

Research output: Contribution to journalArticlepeer-review

2 Citations (Scopus)
85 Downloads (Pure)


Motivated by the ever-growing demand for green wireless communications and the advantages of cell-free (CF) massive multiple-input multiple-output (mMIMO) systems, we focus on the design of their downlink (DL) for optimal energy efficiency (EE). To address this fundamental topic, we assume that each access point (AP) is deployed with multiple antennas and serves multiple users on the same time-frequency resource while the APs are Poisson point process (PPP) distributed, which approaches realistically their opportunistic spatial randomness. Relied on tools from stochastic geometry, we derive a lower bound on the DL average achievable spectral efficiency (SE). Next, we consider a realistic power consumption model for CF mMIMO systems. These steps enable the formulation of a tractable optimization problem concerning the DL EE, which results in the analytical determination of the optimal pilot reuse factor, the AP density, and the number of AP antennas and users that maximize the EE. Hence, we provide useful design guidelines for CF mMIMO systems relating to fundamental system variables towards optimal EE. Among the results, we observe that an optimal pilot reuse factor and AP density exist, while larger values result in an increase of the interference, and subsequently, lower EE. Overall, it is shown that the CF mMIMO technology is a promising candidate for next-generation networks achieving simultaneously high SE and EE.

Original languageEnglish
JournalIEEE Transactions on Green Communications and Networking
Early online date12 Feb 2021
Publication statusEarly online date - 12 Feb 2021

Bibliographical note

Publisher Copyright:

Copyright 2021 Elsevier B.V., All rights reserved.


  • beyond 5G MIMO.
  • Cell-free massive MIMO systems
  • energy efficiency
  • small cells networks
  • stochastic geometry

ASJC Scopus subject areas

  • Renewable Energy, Sustainability and the Environment
  • Computer Networks and Communications


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