IEEE International Symposium on Personal, Indoor and Mobile Radio Communications
12–15 September 2022 // Virtual Conference

Tu06: Beyond-5G Massive MIMO systems: User-centric cell-free networks

Lecturer(s)

Prof. Carmen D’Andrea (University of Cassino and Southern Latium, Italia)

Carmen D’Andrea is currently a non-tenured Assistant Professor at the University of Cassino and Lazio Meridionale, Italy, and an Adjunct Professor at the University of Molise, Italy. She was born in Italy on 16 July 1991 and received her B.S., M.S., and Ph.D. degrees, all with honors, in Telecommunications Engineering from the University of Cassino and Southern Latium, Italy, in 2013, 2015, and 2019 respectively. In 2017, she was a Visiting Ph.D. student with the Wireless Communications (WiCom) Research Group in the Department of Information and Communication Technologies at Universitat Pompeu Fabra in Barcelona, Spain. In the spring of 2020, she spent three months as a visiting researcher with the Communication System Division of the Department of Electrical Engineering at the Linkoping University in Sweden. Since 2020, she is Associate Editor for IEEE Communications Letters and IEEE Open Journal of the Communications Society. She is currently a regular reviewer for several journals and conferences in the communications field and a TPC member of various conference tracks. She has been recently awarded by the Editorial Board of the IEEE Transactions on Communications as Exemplary Reviewer 2021. Her research interests are focused on beyond-5G topics such as cell-free massive MIMO, millimeter-wave and sub-THz wireless networks, beyond-OFDM modulations, joint sensing and communications, and RIS-aided communications.

Prof. Giovanni Interdonato (University of Cassino and Southern Latium, Italia)

Giovanni Interdonato is currently a non-tenured Assistant Professor at the Department of Electrical and Information Engineering of the University of Cassino and Southern Latium. He received the M.Sc. degree in computer and telecommunication systems engineering from the University Mediterranea of Reggio Calabria, Italy, in 2015, and the Ph.D. degree in electrical engineering with specialization in communication systems from Linköping University, Sweden, in 2020. From October 2015 to October 2018, he was a researcher at the radio network department at Ericsson Research in Linköping, and a Marie Sklodowska-Curie research fellow of the H2020 ITN 5Gwireless project. During his Ph.D. studies, he co-invented about 30 filed patent applications (Ericsson’s IP), including the popular Ericsson Radio Stripes concept, and was a recipient of a grant from the Ericsson Research Foundation in 2019. Dr. Interdonato spent six months in 2017/2018 as a visiting Ph.D. student at the Signal Processing and Communications Group of the Universitat Politecnica de Catalunya, Barcelona, Spain. He was a visiting researcher at the Centre Tecnologic de Telecomunicacions de Catalunya, Barcelona, Spain, for six months in 2014, within the Erasmus+ programme. His main research interests include signal processing aspects of beyond-5G technologies, radio resource management and communication protocols, with specific focus on co- located/distributed massive MIMO systems at sub-6GHz and millimetre Wave bands, multi-access edge computing and RIS-aided communications. Currently, he serves as an associate editor for IEEE Communications Letters, and has been recently awarded by the Editorial Board of the IEEE Transactions on Communications as Exemplary Reviewer 2021.

Abstract

This tutorial aims at presenting a comprehensive overview of cell-free massive MIMO (multiple-input multiple-output), illustrating its main benefits and drawbacks, explaining how it works, how it can be analyzed, and highlighting its potentialities and challenges.
Cell-free massive MIMO is one of the key candidate technologies for future 6G wireless networks. While Massive MIMO has played a key role in the deployment of 5G networks, the need for granting more uniform network coverage and for providing as uniform and stable as possible performance across network users has led to the introduction and consideration of this new technology.
The tutorial will present transceiver signal processing and resource allocation schemes tailored for cell-free massive MIMO systems.
Particular attention will be devoted to the discussion of peculiarities of cell-free massive MIMO systems at millimeter wave (mmWave) carrier frequencies. Indeed, despite a distributed network architecture that seems to be ideally suited for coping with the blockage effects and large path loss incurred at such high frequencies, most of the research on this topic has focused on sub-6 GHz frequencies. Topics such as beam alignment and hybrid beamforming schemes will be also tackled.
Overall, the tutorial will present a well-rounded overall picture of such key enabling technology for future 6G Networks.

Motivation and Context

This tutorial aims at presenting a comprehensive overview of cell-free massive MIMO (multiple-input multiple-output), illustrating its main benefits and drawbacks, explaining how it works, how it can be analyzed, and by highlighting its potentialities and challenges.

Cell-free massive MIMO is one of the key candidate technologies for future 6G wireless networks. While Massive MIMO has played a key role in the deployment of 5G networks, the need for granting more uniform network coverage and for providing an as uniform and stable as possible performance across network users has led to the introduction and consideration of this new technology.

In cell-free massive MIMO, many antennas are geographically distributed in low-complexity access points (APs) to serve the users jointly and coherently at the same time-frequency resources and coordinated by one or more central processing units (CPUs).

Cell-free massive MIMO combines the physical layer operation of massive MIMO, the joint coherent signal processing at multiple APs of network MIMO, and the network ultra-densification. In a cell-free massive MIMO system, each user experiences being in the centre of its own tailored cell served by many APs, thereby experiencing no cell boundary effects. Hence, the terminology cell-free.

The tutorial will present transceiver signal processing and resource allocation schemes tailored for cell-free massive MIMO systems. Particular attention will be devoted to the discussion of peculiarities of cell-free massive MIMO systems at millimeter wave (mmWave) carrier frequencies. Indeed, despite a distributed network architecture seems to be ideally suited for coping with the blockage effects and large path loss incurred at such high frequencies, most of the research on this topic has focuses on sub-6 GHz frequencies. Topics such as beam alignment and hybrid beamforming schemes will be also tackled.

Overall, the tutorial will present a well-rounded overall picture of such key enabling technology for future 6G Networks.

Structure and Content

1. Preliminaries on massive MIMO (15 minutes)

  • Key ingredients: beamforming gain, spatial diversity, and spatial multiplexing
  • Favourable propagation and channel hardening
  • Caveats: cell-edge performance, blockage phenomena

2. Beyond-5G distributed multiple-antenna technologies (15 minutes)

  • Motivation: ensuring excellent quality of service and connectivity to everyone
  • Taxonomy and related concepts

3. Cell-free massive MIMO (60 minutes)

  • System model and general characterization
  • Pilot-based uplink and downlink training, Pilot contamination.
  • Overview on coherent precoding and combining schemes.
  • Radio resource allocation: user-centric AP-user association, pilot assignment, power control
  • Cell-free massive MIMO at millimeter-wave: potentialities and challenges

4. Cell-free massive MIMO at millimeter-wave: Potentialities and Challenges (60 minutes)

  • The millimeter-wave propagation and channel models
  • Transceiver signal processing for cell-free at millimeter-wave
  • Description of beam alignment procedure
  • Cell-free massive MIMO and Mobility

5. Practical cell-free networks (30 minutes)

  • Network scalability
  • Hardware impairments, AP synchronization
  • Capacity-limited fronthaul network: quantization and low-dimensional signalling exchange
  • Novel architectures: Radio Stripes, pCell, RadioWeaves