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Cell-free Massive MIMO (multiple-input multiple-output) refers to a distributed Massive MIMO system where all the access points (APs) cooperate to coherently serve all the user equipments (UEs), suppress inter-cell interference and mitigate…

Information Theory · Computer Science 2019-09-09 Giovanni Interdonato , Hien Quoc Ngo , Pål Frenger , Erik G. Larsson

In massive multiple-input multiple-output (MIMO) downlink systems, the physical implementation of the base stations (BSs) requires the use of cheap and power-efficient power amplifiers (PAs) to avoid high hardware cost and high power…

Signal Processing · Electrical Eng. & Systems 2023-09-04 Yatao Liu , Mingjie Shao , Wing-Kin Ma

This work proposes novel approaches that jointly design user equipment (UE) association and power control (PC) in a downlink user-centric cell-free massive multiple-input multiple-output (CFmMIMO) network, where each UE is only served by a…

Information Theory · Computer Science 2024-05-21 Chongzheng Hao , Tung Thanh Vu , Hien Quoc Ngo , Minh N. Dao , Xiaoyu Dang , Chenghua Wang , Michail Matthaiou

This paper takes into consideration the non-ideal efficiency characteristics of realistic power amplifiers (PAs) along with the daily traffic profile in order to investigate the impact of PA dimensioning on the energy efficiency (EE) of…

Networking and Internet Architecture · Computer Science 2014-11-10 M. M. Aftab Hossain , Riku Jäntti , Cicek Cavdar

A Cell-Free Massive MIMO (multiple-input multiple-output) system comprises a very large number of distributed access points (APs)which simultaneously serve a much smaller number of users over the same time/frequency resources based on…

Information Theory · Computer Science 2017-01-18 Hien Quoc Ngo , Alexei Ashikhmin , Hong Yang , Erik G. Larsson , Thomas L. Marzetta

In this work, we consider the downlink of a multi-cell multiple-input multiple-output (MIMO) system and find the jointly optimal number of base station (BS) antennas and transmission powers that minimize the power consumption while…

Information Theory · Computer Science 2019-02-22 Kamil Senel , Emil Björnson , Erik G. Larsson

In multi-user multiple-input multiple-output (MU-MIMO) systems, the non-linear behavior of the power amplifiers (PAs) may cause degradation of the linear precoding schemes dealing with interference between user equipments (UEs), e.g., the…

Signal Processing · Electrical Eng. & Systems 2025-12-03 Juan Vidal Alegría , Ashkan Sheikhi , Ove Edfors

In this paper, we analyze the benefits of including downlink pilots in a cell-free massive MIMO system. We derive an approximate per-user achievable downlink rate for conjugate beamforming processing, which takes into account both uplink…

Information Theory · Computer Science 2019-09-10 Giovanni Interdonato , Hien Quoc Ngo , Erik G. Larsson , Pål Frenger

Cell-free Massive MIMO is considered as a promising technology for satisfying the increasing number of users and high rate expectations in beyond-5G networks. The key idea is to let many distributed access points (APs) communicate with all…

Information Theory · Computer Science 2019-09-19 Emil Björnson , Luca Sanguinetti

Multiple-input multiple-output (MIMO) millimeter wave (mmWave) systems are vulnerable to hardware impairments due to operating at high frequencies and employing a large number of radio- frequency (RF) hardware components. In particular,…

Information Theory · Computer Science 2018-06-06 Nima N. Moghadam , Gábor Fodor , Mats Bengtsson , David J. Love

We consider a cell-free massive multiple-input multiple-output (CF-mMIMO) system with joint unicast and multi-group multicast transmissions. We derive exact closed-form expressions for the downlink achievable spectral efficiency (SE) of…

Information Theory · Computer Science 2024-10-07 Mustafa S. Abbas , Zahra Mobini , Hien Quoc Ngo , Michail Matthaiou

Cell-free massive multiple-input multiple-output (MIMO), with a large number of distributed access points (APs) that jointly serve the user equipments (UEs), is a promising network architecture for future wireless communications. To reduce…

Information Theory · Computer Science 2017-09-12 Jiayi Zhang , Yinghua Wei , Emil Björnson , Yu Han , Xu Li

Due to the nonlinearity of power amplifiers (PAs), the transmit signal is distorted. Previous works have studied the spatial distribution of this distortion for a central massive MIMO array. In this work, we extend the analysis for…

Signal Processing · Electrical Eng. & Systems 2021-06-21 François Rottenberg , Gilles Callebaut , Liesbet Van der Perre

We consider the downlink of a cell-free massive multiple-input multiple-output (MIMO) system where large number of access points (APs) simultaneously serve a group of users. Two fundamental problems are of interest, namely (i) to maximize…

Signal Processing · Electrical Eng. & Systems 2022-01-13 Muhammad Farooq , Hien Quoc Ngo , Le-Nam Tran

Cell-free massive MIMO is a key 6G technology, offering superior spectral and energy efficiency. However, its dense deployment of low-cost access points (APs) makes hardware impairments unavoidable. While narrowband impairments are…

Signal Processing · Electrical Eng. & Systems 2025-07-30 Özlem Tuğfe Demir , Muhammed Selman Somuncu , Ahmet M. Elbir , Emil Björnson

M-MIMO is one of the crucial technologies for increasing spectral and energy efficiency of wireless networks. Most of the current works assume that M-MIMO arrays are equipped with a linear front end. However, ongoing efforts to make…

Machine Learning · Computer Science 2026-04-20 Marcin Hoffmann , Paweł Kryszkiewicz

We consider a cell-free massive MIMO system with multiple antennas on the users and access points. In previous works, the downlink spectral efficiency (SE) has been evaluated using the hardening bound that requires no downlink pilots. This…

Signal Processing · Electrical Eng. & Systems 2024-04-30 Eren Berk Kama , Junbeom Kim , Emil Björnson

We consider a cell-free massive multiple-input multiple-output (MIMO) system with multiple antennas on the users and access points (APs). In previous works, the downlink spectral efficiency (SE) has been evaluated using the hardening bound…

Information Theory · Computer Science 2026-01-01 Eren Berk Kama , Junbeom Kim , Emil Björnson

In this paper, we investigate downlink power control in massive multiple-input multiple-output (MIMO) networks with distributed antenna arrays. The base station (BS) in each cell consists of multiple antenna arrays, which are deployed in…

Information Theory · Computer Science 2020-01-14 Noman Akbar , Emil Björnson , Erik G. Larsson , Nan Yang

The channel hardening effect is less pronounced in the cell-free massive multiple-input multiple-output (mMIMO) system compared to its cellular counterpart, making it necessary to estimate the downlink effective channel gains to ensure…

Information Theory · Computer Science 2024-04-12 Weiyang Xu , Ruiguang Wang , Yuan Zhang , Hien Quoc Ngo , Wei Xiang