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Beyond diagonal reconfigurable intelligent surface (BD-RIS) architectures offer superior beamforming gain over conventional diagonal RISs. However, the channel estimation overhead is the main hurdle for reaping the above gain in practice.…

Signal Processing · Electrical Eng. & Systems 2026-02-25 Rui Wang , Junyuan Gao , Shuowen Zhang , Bruno Clerckx , Liang Liu

In wireless communication, accurate channel state information (CSI) is of pivotal importance. In practice, due to processing and feedback delays, estimated CSI can be outdated, which can severely deteriorate the performance of the…

Signal Processing · Electrical Eng. & Systems 2021-04-02 Muhammad Karam Shehzad , Luca Rose , Mohamad Assaad

Reconfigurable intelligent surface (RIS) is a newly-emerged technology that might fundamentally change how wireless networks are operated. Though extensively studied in recent years, the practical limitations of RIS are often neglected when…

Signal Processing · Electrical Eng. & Systems 2023-12-12 Parisa Ramezani , Yasaman Khorsandmanesh , Emil Björnson

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

Reconfigurable intelligent Surfaces (RIS) and half-duplex decoded and forwarded (DF) relays can collaborate to optimize wireless signal propagation in communication systems. Users typically have different rate demands and are clustered into…

Information Theory · Computer Science 2025-06-04 Huijun Tang , Jieling Zhang , Zhidong Zhao , Huaming Wu , Hongjian Sun , Pengfei Jiao

Simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR-RIS)-aided cell-free massive multiple-input multiple-output (CF-mMIMO) systems are investigated under spatially correlated fading channels using realistic…

Information Theory · Computer Science 2025-01-06 Zeping Sui , Hien Quoc Ngo , Michail Matthaiou , Lajos Hanzo

Cell-Free Massive multiple-input multiple-output (MIMO) and reconfigurable intelligent surface (RIS) are two promising technologies for application to beyond-5G networks. This paper considers Cell-Free Massive MIMO systems with the…

Information Theory · Computer Science 2021-12-20 Trinh Van Chien , Hien Quoc Ngo , Symeon Chatzinotas , Marco Di Renzo , Björn Ottersten

The focus of this letter is on the reduction of the large pilot overhead in orthogonal frequency division multiplexing (OFDM) based massive multiple-input multiple-output (MIMO) systems. We propose a novel joint channel estimation and…

Information Theory · Computer Science 2022-12-16 Danilo Lelin Li , Arman Farhang

We consider a multiuser (MU) multiple-input multiple-output (MIMO) time-division duplexing (TDD) system in which the base station (BS) is equipped with a large number of antennas for communicating with single-antenna mobile users. In such a…

Information Theory · Computer Science 2013-12-05 Ko-Feng Chen , Yen-Cheng Liu , Yu T. Su

We study the channel estimation problem for a reconfigurable intelligent surface (RIS)-assisted millimeter-wave (mmWave) multi-user multiple-input multiple-output (MU-MIMO) system. In particular, it is assumed that the channel between a RIS…

Signal Processing · Electrical Eng. & Systems 2024-10-18 Jeongjae Lee , Songnam Hong

In intelligent reflecting surface (IRS) assisted communication systems, the acquisition of channel state information (CSI) is a crucial impediment for achieving the beamforming gain of IRS because of the considerable overhead required for…

Information Theory · Computer Science 2020-06-25 Zhaorui Wang , Liang Liu , Shuguang Cui

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

Reconfigurable intelligent surface (RIS)-assisted cell-free (CF) multiple-input multiple-output (MIMO) networks can significantly enhance system performance. However, the extensive deployment of RIS elements imposes considerable channel…

Signal Processing · Electrical Eng. & Systems 2025-06-30 Hongqin Ke , Jindan Xu , Wei Xu , Chau Yuen , Zhaohua Lu

To achieve the more significant passive beamforming gain in the double-intelligent reflecting surface (IRS) aided system over the conventional single-IRS counterpart, channel state information (CSI) is indispensable in practice but also…

Information Theory · Computer Science 2021-03-12 Beixiong Zheng , Changsheng You , Rui Zhang

For downlink massive multiple-input multiple-output (MIMO) operating in time-division duplex protocol, users can decode the signals effectively by only utilizing the channel statistics as long as channel hardening holds. However, in a…

Information Theory · Computer Science 2022-05-17 Tung T. Vu , Trinh Van Chien , Canh T. Dinh , Hien Quoc Ngo , Michail Matthaiou

In this paper, we consider and study a cell-free massive MIMO (CF-mMIMO) system aided with reconfigurable intelligent surfaces (RISs), where a large number of access points (APs) cooperate to serve a smaller number of users with the help of…

Information Theory · Computer Science 2021-05-17 Bayan Al-Nahhas , Mohanad Obeed , Anas Chaaban , Md. Jahangir Hossain

In wireless communication Multiple Input Multiple Output (MIMO) technology has brought significant improvement in service by adopting Orthogonal Frequency Division Multiplexing (OFDM), a digital modulation technique. To achieve great…

Networking and Internet Architecture · Computer Science 2024-05-14 Shahriar Hassan , Umme Farhana , Md Karam Newaz

Reconfigurable intelligent surfaces (RISs) have recently received widespread attention in the field of wireless communication. An RIS can be controlled to reflect incident waves from the transmitter towards the receiver; a feature that is…

Information Theory · Computer Science 2021-09-15 Jiangfeng Hu , Haifan Yin , Emil Björnson

We investigate a general channel estimation problem in the massive multiple-input multiple-output (MIMO) system which employs the hybrid analog/digital precoding structure with limited radio-frequency (RF) chains. By properly designing RF…

Information Theory · Computer Science 2017-12-27 Leyuan Pan , Le Liang , Wei Xu , Xiaodai Dong

This paper considers a simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR-RIS)-aided cell-free massive multiple-input multiple-output (CF-mMIMO) system, accounting for imperfect hardware in spatially…

Information Theory · Computer Science 2024-08-27 Zeping Sui , Hien Quoc Ngo , Michail Matthaiou