University of Oulu

N. T. Nguyen et al., "Fairness Enhancement of UAV Systems with Hybrid Active-Passive RIS," in IEEE Transactions on Wireless Communications, doi: 10.1109/TWC.2023.3317934.

Fairness enhancement of UAV systems with hybrid active-passive RIS

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Author: Nguyen, Nhan Thanh1; Nguyen, Van-Dinh2,3; Van Nguyen, Hieu4;
Organizations: 1Centre for Wireless Communications, University of Oulu, P.O.Box 4500, Finland
2College of Engineering and Computer Science, Hanoi, Vietnam
3Center for Environmental Intelligence, VinUniversity, Vinhomes Ocean Park, Hanoi, Vietnam
4Faculty of Electronic and Telecommunication Engineering, The University of Danang, University of Science and Technology, Da Nang, Vietnam
5Department of Electronic Engineering, Shanghai Jiao Tong University, China
6Interdisciplinary Centre for Security, Reliability and Trust (SnT), University of Luxembourg, Luxembourg
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 1.8 MB)
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Language: English
Published: Institute of Electrical and Electronics Engineers, 2023
Publish Date: 2023-10-31


We consider unmanned aerial vehicle (UAV)-enabled wireless systems where downlink communications between a multi-antenna UAV and multiple users are assisted by a hybrid active-passive reconfigurable intelligent surface (RIS). We aim at a fairness design of two typical UAV-enabled networks, namely the static-UAV network where the UAV is deployed at a fixed location to serve all users at the same time, and the mobile-UAV network which employs the time division multiple access protocol. In both networks, our goal is to maximize the minimum rate among users through jointly optimizing the UAV’s location/trajectory, transmit beamformer, and RIS coefficients. The resulting problems are highly nonconvex due to a strong coupling between the involved variables. We develop efficient algorithms based on block coordinate ascend and successive convex approximation to effectively solve these problems in an iterative manner. In particular, in the optimization of the mobile-UAV network, closed-form solutions to the transmit beamformer and RIS passive coefficients are derived. Numerical results show that a hybrid RIS equipped with only 4 active elements and a power budget of 0 dBm offers an improvement of 38% — 63% in minimum rate, while that achieved by a passive RIS is only about 15%, with the same total number of elements.

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Series: IEEE transactions on wireless communications
ISSN: 1536-1276
ISSN-E: 1558-2248
ISSN-L: 1536-1276
Volume: Online first
DOI: 10.1109/twc.2023.3317934
Type of Publication: A1 Journal article – refereed
Field of Science: 213 Electronic, automation and communications engineering, electronics
Copyright information: This work is licensed under a Creative Commons Attribution 4.0 License. For more information, see