University of Oulu

N. T. Nguyen, V. -D. Nguyen, H. V. Nguyen, H. Q. Ngo, S. Chatzinotas and M. Juntti, "Spectral Efficiency Analysis of Hybrid Relay-Reflecting Intelligent Surface-Assisted Cell-Free Massive MIMO Systems," in IEEE Transactions on Wireless Communications, vol. 22, no. 5, pp. 3397-3416, May 2023, doi: 10.1109/TWC.2022.3217828

Spectral efficiency analysis of hybrid relay-reflecting intelligent surface-assisted cell-Free massive MIMO systems

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Author: Nguyen, Nhan Thanh1; Nguyen, Van-Dinh2; Nguyen, Hieu Van3;
Organizations: 1Centre for Wireless Communications, University of Oulu, 90014 Oulu, Finland
2College of Engineering and Computer Science, VinUniversity, Hanoi 100000, Vietnam
3Faculty of Electronics and Telecommuni- cation Engineering, The University of Danang—University of Science and Technology, Da Nang 50000, Vietnam
4School of Electronics, Electrical Engineering and Computer Science, Queen’s University Belfast, BT7 1NN Belfast, U.K.
5Interdisciplinary Centre for Security, Reliability and Trust (SnT), University of Luxembourg, L-1855 Esch-sur- Alzette, Luxembourg
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 2.3 MB)
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Language: English
Published: Institute of Electrical and Electronics Engineers, 2022
Publish Date: 2023-09-13


A cell-free (CF) massive multiple-input-multiple-output (mMIMO) system can provide uniform spectral efficiency (SE) with simple signal processing. On the other hand, a recently introduced technology called hybrid relay-reflecting intelligent surface (HR-RIS) can customize the physical propagation environment by simultaneously reflecting and amplifying radio waves in preferred directions. Thus, it is natural that incorporating HR-RIS into CF mMIMO can be a symbiotic convergence of these two technologies for future wireless communications. This motivates us to consider an HR-RIS-aided CF mMIMO system to utilize their combined benefits. We first model the uplink/downlink channels and derive the minimum-mean-square-error estimate of the effective channels. We then present a comprehensive analysis of SE performance of the considered system. Specifically, we derive closed-form expressions for the uplink and downlink SE. The results reveal important observations on the performance gains achieved by HR-RISs compared to conventional systems. The presented analytical results are also valid for conventional CF mMIMO systems and those aided by passive reconfigurable intelligent surfaces. Such results play an important role in designing new transmission strategies and optimizing HR-RIS-aided CF mMIMO systems. Finally, we provide extensive numerical results to verify the analytical derivations and the effectiveness of the proposed system design under various settings.

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Series: IEEE transactions on wireless communications
ISSN: 1536-1276
ISSN-E: 1558-2248
ISSN-L: 1536-1276
Volume: 22
Issue: 5
Pages: 3397 - 3416
DOI: 10.1109/TWC.2022.3217828
Type of Publication: A1 Journal article – refereed
Field of Science: 213 Electronic, automation and communications engineering, electronics
Funding: The work of Nhan Thanh Nguyen and Markku Juntti was supported in part by the Academy of Finland under 6Genesis Flagship under Grant 318927, in part by the EERA Project under Grant 332362, and in part by the Infotech Program Funded by the University of Oulu Graduate School. The work of Van-Dinh Nguyen, Hieu Van Nguyen, and Symeon Chatzinotas was supported by the Luxembourg National Research Fund (FNR)—RISOTTI Project, ref. FNR/C20/IS/14773976/RISOTTI. The work of Hien Quoc Ngo was supported by the U.K. Research and Innovation Future Leaders Fellowships under Grant MR/S017666/1.
Academy of Finland Grant Number: 318927
Detailed Information: 318927 (Academy of Finland Funding decision)
332362 (Academy of Finland Funding decision)
Copyright information: © The Author(s) 2022. This work is licensed under a Creative Commons Attribution 4.0 License. For more information, see