Scalable Cell-Free Massive MIMO Systems

By Emil Björnson, Luca Sanguinetti. IEEE Transactions on Communications, 2019

945 citations recorded by the source corpus.

Imagine a coverage area with many wireless access points that cooperate to jointly serve the users, instead of creating autonomous cells. Such a cell-free network operation can potentially resolve many of the interference issues that appear in current cellular networks. This ambition was previously called Network MIMO (multiple-input multiple-output) and has recently reappeared under the name Cell-Free Massive MIMO. The main challenge is to achieve the benefits of cell-free operation in a practically feasible way, with computational complexity and fronthaul requirements that are scalable to large networks with many users. We propose a new framework for scalable Cell-Free Massive MIMO systems by exploiting the dynamic cooperation cluster concept from the Network MIMO literature. We provide a novel algorithm for joint initial access, pilot assignment, and cluster formation that is proved to be scalable. Moreover, we adapt the standard channel estimation, precoding, and combining methods to become scalable. A new uplink and downlink duality is proved and used to heuristically design the precoding vectors on the basis of the combining vectors. Interestingly, the proposed scalable precoding and combining outperform conventional maximum ratio (MR) processing and also performs closely to the best unscalable alternatives.

Subfields: Computer Networks and Communications, Electrical and Electronic Engineering

View Paper: https://www.semanticscholar.org/paper/dd344eb6ffc51d355703cdaa13ab915f515384f3

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In Computer Networks and Communications

In Electrical and Electronic Engineering

Citations in the corpus

What Will the Future of UAV Cellular Communications Be? A Flight From 5G to 6G (2021, background): “Research is ongoing on various aspects of cell-free operation that are still not fully resolved, including scalability [147],”
Foundations of User-Centric Cell-Free Massive MIMO (2020, methodology): “A framework for creating the user-centric clusters in a decentralized fashion was proposed in [29], where the scalability of the different signal processing tasks was also analyzed.”
Prospective Multiple Antenna Technologies for Beyond 5G (2019, methodology): “There is also a series of papers that consider partially centralized precoding and combining for cell-free massive MIMO [46], [54], [57], [63].”
A Comprehensive Overview on 5G-and-Beyond Networks With UAVs: From Communications to Sensing and Intelligence (2020, background): “Nevertheless, key issues that remain to be solved include efficient centralized and distributed power control, low-complexity fronthaul/backhaul provisioning, and network scalability with respect to UAV swarms [85]–[88].”
Understanding O-RAN: Architecture, Interfaces, Algorithms, Security, and Research Challenges (2022, background): “Another extension can combine the centralized control of the O-RAN architecture with cell-free cellular networks (i.e., a version of massive MIMO with distributed antennas and centralized processing) [214], providing support for coordination across the different antenna endpoints.”
User-Centric Cell-Free Massive MIMO Networks: A Survey of Opportunities, Challenges and Solutions (2021, methodology): “Distributed resource allocation schemes help scale down the complexity of optimized resource allocation.”