University of Oulu

N. T. Nguyen, Q. -D. Vu, K. Lee and M. Juntti, "Hybrid Relay-Reflecting Intelligent Surface-Assisted Wireless Communications," in IEEE Transactions on Vehicular Technology, vol. 71, no. 6, pp. 6228-6244, June 2022, doi: 10.1109/TVT.2022.3158686

Hybrid relay-reflecting intelligent surface-assisted wireless communications

Saved in:
Author: Nguyen, Nhan Thanh1; Vu, Quang-Doanh2,3; Lee, Kyungchun4;
Organizations: 1Centre for Wireless Communications, University of Oulu, P.O.Box 4500, FI-90014, Finland
2Centre for Wireless Communications, University of Oulu
3Present address: Mobile Networks, Nokia, 90650 Oulu, Finland
4Department of Electrical and Information Engineering, Seoul National University of Science and Technology, Seoul 01811, Republic of Korea
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 1.4 MB)
Persistent link:
Language: English
Published: Institute of Electrical and Electronics Engineers, 2022
Publish Date: 2022-06-09


Reconfigurable intelligent surface (RIS) has emerged as a cost- and energy-efficient solution to enhance the wireless communications capacity. However, recent studies show that a very large surface is required for a RIS-assisted communications system; otherwise, they may be outperformed by the conventional relay. Furthermore, the performance gain of a RIS can be considerably degraded by hardware impairments such as limited-resolution phase shifters. To overcome those challenges, we propose a hybrid relay-reflecting intelligent surface (HR-RIS) architecture, in which a single or few elements serve as active relays, while the remaining only reflect the incident signals. We propose two HR-RIS architectures, namely, the fixed and dynamic HR-RIS. The joint transmit beamforming at the base station and hybrid relay-reflecting at the HR-RIS are designed based on alternating optimization and power allocation strategies. The simulation results for a 4x4 multiple-input multiple-output system show that the proposed HR-RIS with only a single active element can achieve about 95% and 75% improvement in spectral efficiency and energy efficiency, respectively, with respect to the conventional RIS-aided system. The results also show that the HR-RIS can outperform the conventional relaying scheme in most of the considered scenarios.

see all

Series: IEEE transactions on vehicular technology
ISSN: 0018-9545
ISSN-E: 1939-9359
ISSN-L: 0018-9545
Volume: 71
Issue: 6
Pages: 6228 - 6244
DOI: 10.1109/TVT.2022.3158686
Type of Publication: A1 Journal article – refereed
Field of Science: 213 Electronic, automation and communications engineering, electronics
Funding: This work has been supported in part by Academy of Finland under 6G Flagship (grant 318927), EERA Project (grant 332362), and Infotech Program funded by University of Oulu Graduate School.
Academy of Finland Grant Number: 318927
Detailed Information: 318927 (Academy of Finland Funding decision)
332362 (Academy of Finland Funding decision)
Copyright information: © The Authors. This work is licensed under a Creative Commons Attribution 4.0 License. For more information, see