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Reconfigurable intelligent surfaces (RISs) have been introduced as a remedy for mitigating frequent blockages in millimeter wave (mmWave) multiple-input multiple-output (MIMO) communication networks. However, perfect or nearly perfect…

Signal Processing · Electrical Eng. & Systems 2021-06-22 Rafaela Schroeder , Jiguang He , Markku Juntti

Reconfigurable intelligent surface (RIS) has been widely discussed as new technology to improve wireless communication performance. Based on the unique design of RIS, its elements can reflect, refract, absorb, or focus the incoming waves…

Signal Processing · Electrical Eng. & Systems 2020-09-03 Salah Eddine Zegrar , Liza Afeef , Huseyin Arslan

Reconfigurable intelligent surfaces (RISs) have been proposed recently as new technology to tune the wireless propagation channels in real-time. However, most of the current works assume single-RIS (S-RIS)-aided systems, which can be…

Signal Processing · Electrical Eng. & Systems 2021-09-21 Khaled Ardah , Sepideh Gherekhloo , André L. F. de Almeida , Martin Haardt

Intelligent reflecting surface (IRS) is envisioned as a promising technology to broaden signal coverage and enhance transmission in terahertz (THz) communications. Due to the passivity of IRS, the channel measurement can not be achieved by…

Information Theory · Computer Science 2020-03-17 Boyu Ning , Zhi Chen , Wenrong Chen , Yiming Du

This study centers on Line-of-Sight (LoS) MIMO communication enabled by a Transmissive Reconfigurable Intelligent Surface (RIS) operating in the Terahertz (THz) frequency bands. The study demonstrates that the introduction of RIS can render…

Information Theory · Computer Science 2023-12-05 Nithish Sharvirala , Amine Mezghani , Ekram Hossain

Reconfigurable intelligent surfaces (RISs) consist of many passive elements of metamaterials whose impedance can be controllable to change the characteristics of wireless signals impinging on them. Channel estimation is a critical task when…

Information Theory · Computer Science 2023-09-14 Özlem Tuğfe Demir , Emil Björnson

Reconfigurable intelligent surfaces (RISs) have been recently considered as a promising candidate for energy-efficient solutions in future wireless networks. Their dynamic and lowpower configuration enables coverage extension, massive…

Information Theory · Computer Science 2022-07-05 Li Wei , Chongwen Huang , Qinghua Guo , Zhaohui Yang , Zhaoyang Zhang , George C. Alexandropoulos , Merouane Debbah , Chau Yuen

Considering the dimensionality of a typical reconfigurable intelligent surface (RIS), channel state information acquisition in RIS-assisted systems requires lengthy pilot transmissions. Moreover, the large aperture of the RIS may cause…

Signal Processing · Electrical Eng. & Systems 2023-12-27 Mehdi Haghshenas , Parisa Ramezani , Maurizio Magarini , Emil Björnson

A reconfigurable intelligent surface (RIS) reflects incoming signals in different ways depending on the phase-shift pattern assigned to its elements. The most promising use case is to aid the communication between a base station and a user…

Information Theory · Computer Science 2022-12-06 Emil Björnson , Parisa Ramezani

In reconfigurable intelligent surface (RIS)-assisted millimeter-wave (mmWave) communication systems, the large-scale RIS introduces pronounced geometric effects that lead to the coexistence of far-field and near-field propagation.…

Signal Processing · Electrical Eng. & Systems 2026-02-09 Xiaokun Tuo , Ming-Min Zhao , Xiang Wang , Changsheng You , Min-Jian Zhao

Channel estimation in reconfigurable intelligent surfaces (RIS)-aided systems is crucial for optimal configuration of the RIS and various downstream tasks such as user localization. In RIS-aided systems, channel estimation involves…

Signal Processing · Electrical Eng. & Systems 2023-12-19 Firas Fredj , Amal Feriani , Amine Mezghani , Ekram Hossain

Reconfigurable intelligent surfaces (RISs) have attracted increasing interest from both academia and industry, thanks to their unique features on controlling electromagnetic (EM) waves. Although theoretical models for RIS-empowered…

Information Theory · Computer Science 2024-03-05 Jian Sang , Jifeng Lan , Mingyong Zhou , Boning Gao , Wankai Tang , Xiao Li , Michail Matthaiou , Shi Jin , Marco Di Renzo

A reconfigurable intelligent surface (RIS) can be used to improve the channel gain between a base station (BS) and user equipment (UE), but only if its $N$ reflecting elements are configured properly. This requires accurate estimation of…

Signal Processing · Electrical Eng. & Systems 2022-05-24 Özlem Tuğfe Demir , Emil Björnson , Luca Sanguinetti

This paper studies wideband channel estimation for OFDM systems assisted by extremely large RIS (XL-RIS). Due to the large aperture of XL-RISs, the user equipment may operate in the near-field region, while the base station-XL-RIS link…

Signal Processing · Electrical Eng. & Systems 2026-03-24 Lanqing Zhi , Hongwei Wang , Lingxiang Li , Zhi Chen

Channel estimation is challenging for the reconfigurable intelligence surface (RIS) assisted millimeter wave (mmWave) communications. Since the number of coefficients of the cascaded channels in such systems is closely dependent on the…

Signal Processing · Electrical Eng. & Systems 2021-06-22 Yushan Liu , Shun Zhang , Feifei Gao , Jie Tang , Octavia A. Dobre

Accurate channel estimation is essential to achieve the performance gains promised by the use of reconfigurable intelligent surfaces (RISs) in wireless communications. In the uplink of multi-user orthogonal frequency division multiple…

Signal Processing · Electrical Eng. & Systems 2022-01-25 Sumin Jeong , Arman Farhang , Nemanja Stefan Perović , Mark F. Flanagan

Reconfigurable intelligent surfaces (RISs) are one of the foremost technological enablers of future wireless systems. They improve communication and localization by providing a strong non-line-of-sight path to the receiver. In this paper,…

Signal Processing · Electrical Eng. & Systems 2022-04-26 Kamran Keykhosravi , Henk Wymeersch

In this letter, the channel estimation problem is studied for wireless communication systems assisted by large intelligent surface. Due to features of assistant channel, channel estimation (CE) problem for the investigated system is shown…

Information Theory · Computer Science 2019-11-07 Junliang Lin , Gongpu Wang , Rongfei Fan , Theodoros A. Tsiftsis , Chintha Tellambura

Accurate channel modeling is essential for realizing the potential of terahertz (THz) communications in 6G indoor networks, where existing models struggle with severe frequency selectivity and multipath effects. We propose a physically…

Signal Processing · Electrical Eng. & Systems 2025-10-07 Ziang Zhao , Weixi Liang , Kai Hu , Qun Zhang , Xiongbin Yu , Qiang Li

Terahertz (THz) communication signals are susceptible to severe degradation because of the molecular interaction with the atmosphere in the form of subsequent absorption and re-radiation. Recently, reconfigurable intelligent surface (RIS)…

Signal Processing · Electrical Eng. & Systems 2022-10-04 Anish Pradhan , Mohamed A. Abd-Elmagid , Harpreet S. Dhillon , Andreas F. Molisch