In this paper, the downlink of cell-free massive multiple-input multiple-output (MIMO) with zero-forcing processing is considered. To maximize the system energy efficiency (EE), we design power allocation algorithms taking into account imperfect channel state information, hardware, and backhaul power consumption. The total EE optimization problem is nonconvex, which traditionally is solved by the successive convex approximation framework which involves second order cone programs (SOCPs). As such methods have high complexity, the run time is extremely long, especially in large-scale systems with thousands of access points (APs) and users. To overcome this problem, in this paper, we propose to apply two computationally efficient methods, namely proximal gradient (PG) method and accelerated proximal gradient (APG) method to solve the considered problem. Numerical results show that, compared to the conventional SOCPs approximation methods, our proposed methods achieve the same performance while the run time is much smaller.
Bibliographical noteFunding Information:
Hien Quoc Ngo received the B.S. degree in electrical engineering from the Ho Chi Minh City University of Technology, Vietnam, in 2007, the M.S. degree in electronics and radio engineering from Kyung Hee University, South Korea, in 2010, and the Ph.D. degree in communication systems from Linköping University (LiU), Sweden, in 2015. In 2014, he visited the Nokia Bell Labs, Murray Hill, New Jersey, USA. From January 2016 to April 2017, Hien Quoc Ngo was a VR researcher at the Department of Electrical Engineering (ISY), LiU. He was also a Visiting Research Fellow at the School of Electronics, Electrical Engineering and Computer Science, Queen’s University Belfast, UK, funded by the Swedish Research Council.
Parts of this work were presented at the 2020 ICCE Conference Mai et al. (2021)  .The work of Trang C. Mai and Hien Quoc Ngo was supported by the UK Research and Innovation Future Leaders Fellowships under Grant MR/S017666/1 . The work of Le-Nam Tran was supported in part by a Grant from Science Foundation Ireland under Grant number 17/CDA/4786 .
© 2021 Elsevier B.V.
- Accelerated proximal gradient
- Cell-free massive MIMO
- Energy efficiency
- First order
- Proximal gradient
ASJC Scopus subject areas
- Electrical and Electronic Engineering