Hybrid relay-reflecting intelligent surface-assisted wireless communications
Nguyen, Nhan Thanh; Vu, Quang-Doanh; Lee, Kyungchun; Juntti, Markku (2022-03-11)
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
© The Authors. This work is licensed under a Creative Commons Attribution 4.0 License. For more information, see https://creativecommons.org/licenses/by/4.0/.
https://creativecommons.org/licenses/by/4.0/
https://urn.fi/URN:NBN:fi-fe2022060945106
Tiivistelmä
Abstract
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.
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