Abstract
Simultaneously transmitting and reflecting reconfigurable intelligent surfaces (STAR-RISs) have been attracting significant attention in both academia and industry for their advantages of achieving 360° coverage and enhanced degrees-of-freedom. This article first identifies the fundamentals of STAR-RIS, by discussing the hardware models, channel models, and signal models. Then, three representative categorizing approaches for STAR-RISs are introduced from the phase-shift, directional, and energy consumption perspectives. Furthermore, the beamforming design of STAR-RISs is investigated for both independent and coupled phase-shift cases. As a recent advance, a general optimization framework, which has high compatibility and provable optimality regardless of the application scenarios, is proposed. As a further advance, several promising applications are discussed to demonstrate the potential benefits of applying STAR-RISs in sixth-generation wireless communication. Lastly, a few future directions and research opportunities are highlighted.
摘要
融合透射与反射智能超表面(STAR-RIS)因其可实现360°覆盖和增强自由度的优势而备受学术界和工业界关注. 本文首先从硬件模型、 信道模型和信号模型3个角度概述STAR-RIS的基本原理. 随后, 从相移、 方向性和能耗角度介绍STAR-RIS的3种代表性分类方法. 本文还研究了独立相移和耦合相移情况下STAR-RIS的波束成形设计, 并针对两种相移模型提出一个通用优化框架. 该框架具有很高的兼容性和可证明的最优性, 并且不受应用场景限制. 为展现STAR-RIS的潜在优势, 进一步讨论了STAR-RIS在第六代无线通信(6G)中几个前景广阔的应用. 最后, 针对性地探讨了STAR-RIS未来的研究方向和机遇.
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Yuanwei LIU (lead), Jiaqi XU, Zhaolin WANG, and Xidong MU drafted the paper. Jianhua ZHANG and Ping ZHANG revised and finalized the paper.
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Jianhua ZHANG and Ping ZHANG are executive associate editor-in-chief and associate editor-in-chief of Frontiers of Information Technology & Electronic Engineering respectively, and they were not involved with the peer review process of this paper. All the authors declare that they have no conflict of interest.
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Project supported by CHIST-ERA (SUNRISE CHIST-ERA-20-SICT-005), the Engineering and Physical Sciences Research Council (No. EP/W035588/1), and the PHC Alliance Franco-British Joint Research Programme (No. 822326028)
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Liu, Y., Xu, J., Wang, Z. et al. Simultaneously transmitting and reflecting (STAR) RISs for 6G: fundamentals, recent advances, and future directions. Front Inform Technol Electron Eng 24, 1689–1707 (2023). https://doi.org/10.1631/FITEE.2300490
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DOI: https://doi.org/10.1631/FITEE.2300490
Key words
- Sixth-generation wireless communication (6G)
- Reconfigurable intelligent surface (RIS)
- Smart radio environment
- Simultaneous transmission and reflection