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Uplink Postcoding in User-Cluster-Centric Cell-Free Massive MIMO

Ryo TAKAHASHI, Hidenori MATSUO, Sijie XIA, Qiang CHEN, Fumiyuki ADACHI

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Summary :

Cell-free massive MIMO (CF-mMIMO), which cooperatively utilizes a large number of antennas deployed over a communication area, has been attracting great attention as an important technology for realizing 5G-advanced and 6G systems. Recently, to ensure system scalability and mitigate inter-user interference in CF-mMIMO, a user-centric (UC) approach was investigated. In this UC approach, user-centric antenna-sets are formed by selecting appropriate antennas for each user, and postcoding is applied to reduce the strong interference from users whose antenna-sets overlap. However, in very high user density environments, since the number of interfering users increases due to increased overlapping of antenna-sets, the achievable link capacity may degrade. In this paper, we propose a user-cluster-centric (UCC) approach, which groups neighborhood users into a user-cluster and associates the predetermined number of antennas to this user-cluster for spatial multiplexing. We derive the uplink postcoding weights and explain the effectiveness of the proposed UCC approach in terms of the computational complexity of the weight computation. We also compare the uplink user capacities achievable with UC and UCC approaches by computer simulation and clarify situations where the UCC approach is effective. Furthermore, we discuss the impact of the number of interfering users considered in the zero-forcing and minimum mean square error postcoding weight computation on the user capacity.

Publication
IEICE TRANSACTIONS on Communications Vol.E106-B No.9 pp.748-757
Publication Date
2023/09/01
Publicized
2023/03/08
Online ISSN
1745-1345
DOI
10.1587/transcom.2022FGT0001
Type of Manuscript
Special Section PAPER (Special Section on Technologies and Proof-of-Concept Activities for 5G Advanced and 6G)
Category

Authors

Ryo TAKAHASHI
  Tohoku University
Hidenori MATSUO
  Tohoku University
Sijie XIA
  Tohoku University
Qiang CHEN
  Tohoku University
Fumiyuki ADACHI
  Tohoku University

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