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Optimally extracting the advantages available from reconfigurable intelligent surfaces (RISs) in wireless communications systems requires estimation of the channels to and from the RIS. The process of determining these channels is…

Information Theory · Computer Science 2021-10-04 A. Lee Swindlehurst , Gui Zhou , Rang Liu , Cunhua Pan , Ming Li

The emerging reconfigurable intelligent surface (RIS) technology is promising for applications in the millimeter wave (mmWave) communication systems to effectively compensate for propagation loss or tackle the blockage issue. Considering…

Signal Processing · Electrical Eng. & Systems 2023-02-08 Yu Liu , Ming Chen , Cunhua Pan , Yijin Pan , Yinlu Wang , Yaoming Huang , Tianyang Cao , Jiangzhou Wang

Accurate estimation of the cascaded channel from a user equipment (UE) to a base station (BS) via each reconfigurable intelligent surface (RIS) element is critical to realizing the full potential of the RIS's ability to control the overall…

Signal Processing · Electrical Eng. & Systems 2024-11-08 Özlem Tuğfe Demir , Emil Björnson , Luca Sanguinetti

A reconfigurable intelligent surface (RIS) is a holographic MIMO surface composed of a large number of passive elements that can induce adjustable phase shifts to the impinging waves. By creating virtual line-of-sight (LOS) paths between…

Signal Processing · Electrical Eng. & Systems 2023-04-06 Mehdi Haghshenas , Parisa Ramezani , Maurizio Magarini , Emil Björnson

In this letter, we study efficient uplink channel estimation design for a simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR-RIS) assisted two-user communication systems. We first consider the time switching…

Information Theory · Computer Science 2021-12-03 Chenyu Wu , Changsheng You , Yuanwei Liu , Xuemai Gu , Yunlong Cai

Reconfigurable Intelligent Surface (RIS) technology has emerged as a key enabler for future wireless communications. However, its potential is constrained by the difficulty of acquiring accurate user-to-RIS channel state information (CSI),…

Signal Processing · Electrical Eng. & Systems 2026-04-20 Md. Shahriar Sadid , Ali A. Nasir , Saad Al-Ahmadi , Samir Al-Ghadhban

Reconfigurable intelligent surfaces (RISs) can establish favorable wireless environments to combat the severe attenuation and blockages in millimeter-wave (mmWave) bands. However, to achieve the optimal enhancement of performance, the…

Information Theory · Computer Science 2022-03-02 Muxin He , Jindan Xu , Wei Xu , Hong Shen , Ning Wang , Chunming Zhao

This work studies the problems of channel estimation and beamforming for active reconfigurable intelligent surface (RIS)-assisted multiple-input multiple-output (MIMO) communication, incorporating the mutual coupling (MC) effect through an…

Signal Processing · Electrical Eng. & Systems 2025-07-31 Pinjun Zheng , Simon Tarboush , Hadi Sarieddeen , Tareq Y. Al-Naffouri

Reconfigurable intelligent surface (RIS) is a newly-emerged technology that, with its unique features, is considered to be a game changer for future wireless networks. Channel estimation is one of the most critical challenges for the…

Signal Processing · Electrical Eng. & Systems 2023-03-30 Mehdi Haghshenas , Parisa Ramezani , Emil Björnson

Channel estimation is the main hurdle to reaping the benefits promised by the intelligent reflecting surface (IRS), due to its absence of ability to transmit/receive pilot signals as well as the huge number of channel coefficients…

Signal Processing · Electrical Eng. & Systems 2021-06-23 Rui Wang , Liang Liu , Shuowen Zhang , Changyuan Yu

The sparsity of millimeter wave (mmWave) channels in the angular and temporal domains is beneficial to channel estimation, while the associated channel parameters can be utilized for localization. However, line-of-sight (LoS) blockage poses…

Signal Processing · Electrical Eng. & Systems 2024-02-27 Kunlun Li , Jiguang He , Mohammed El-Hajjar , Lie-Liang Yang

This chapter focuses on a hardware architecture for semi-passive Reconfigurable Intelligent Surfaces (RISs) and investigates its consideration for boosting the performance of Multiple-Input Multiple-Output (MIMO) communication systems. The…

Signal Processing · Electrical Eng. & Systems 2025-06-19 George C. Alexandropoulos , Konstantinos D. Katsanos , Evangelos Vlachos

Recent research has focused on reconfigurable intelligent surface (RIS)-assisted cell-free systems with the goal of enhancing coverage and lowering the cost of cell-free networks. However, current research makes the assumption that the…

Signal Processing · Electrical Eng. & Systems 2022-07-29 Songjie Yang , Chenfei Xie , Mingwei Wang , Zhongpei Zhang

Reconfigurable intelligent surfaces (RIS) can be crucial in next-generation communication systems. However, designing the {RIS} phases according to the instantaneous channel state information (CSI) can be challenging in practice due to the…

Information Theory · Computer Science 2023-09-26 Athira Subhash , Abla Kammoun , Ahmed Elzanaty , Sheetal Kalyani , Yazan H. Al-Badarneh , Mohamed-Slim Alouini

The upper mid-band (UMB) spectrum is a key enabler for 6G systems, yet reconfigurable intelligent surface (RIS)-assisted UMB communications face severe channel estimation challenges due to near-field propagation and transitional scattering,…

Signal Processing · Electrical Eng. & Systems 2026-03-09 Jeongjae Lee , Chanwon Kim , Songnam Hong

Reconfigurable intelligent surface (RIS) is a recent low-cost and energy-efficient technology with potential applicability for future wireless communications. Performance gains achieved by employing RIS directly depend on accurate channel…

Signal Processing · Electrical Eng. & Systems 2024-12-24 Paulo R. B. Gomes , Amarilton L. Magalhães , André L. F. de Almeida

The deployment of multiple reconfigurable intelligent surfaces (RISs) enhances the propagation environment by improving channel quality, but it also complicates channel estimation. Following the conventional wireless communication system…

Information Theory · Computer Science 2024-11-22 Weicong Chen , Yu Han , Chao-Kai Wen , Xiao Li , Shi Jin

Channel estimation is one of the key challenges for the deployment of extremely large-scale reconfigurable intelligent surface (XL-RIS) assisted multiple-input multiple-output (MIMO) systems. In this paper, we study the channel estimation…

Signal Processing · Electrical Eng. & Systems 2024-04-29 Jeongjae Lee , Hyeongjin Chung , Yunseong Cho , Sunwoo Kim , Songnam Hong

In this paper, we develop a low-complexity channel estimation for hybrid millimeter wave (mmWave) systems, where the number of radio frequency (RF) chains is much less than the number of antennas equipped at each transceiver. The proposed…

Information Theory · Computer Science 2017-03-14 Lou Zhao , Derrick Wing Kwan Ng , Jinhong Yuan

Reconfigurable intelligent surface is a potential technology component of future wireless networks due to its capability of shaping the wireless environment. The promising MIMO systems in terms of extended coverage and enhanced capacity…

Information Theory · Computer Science 2022-07-07 Paulo R. B. Gomes , Gilderlan T. de Araújo , Bruno Sokal , André L. F. de Almeida , Behrooz Makki , Gábor Fodor