Multi-Hop RIS-Empowered Terahertz Communications: A DRL-Based Hybrid Beamforming Design

Huang, Chongwen; Yang, Zhaohui; Alexandropoulos, George C.; Xiong, Kai; Li, Wei; Yuen, Chau; Zhang, Zhaoyang; Debbah, Mérouane

doi:10.1109/jsac.2021.3071836

Cited by 336 publications

(150 citation statements)

References 56 publications

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“…In this method, by observing the predefined rewards with state and action spaces, the joint design of active and passive beamforming is optimized through trial-and-error interactions with the environment. Specifically, DRL based methods were applied in the RIS-aided multi-user systems to solve spectrum-efficiency optimization problem in [98], secure capacity optimization problem in [99], energy-efficiency optimization problem in [100], and the Terahertz communication in [101].…”

Section: Deep Reinforcement Learning Based Methodsmentioning

confidence: 99%

Reconfigurable intelligent surfaces for smart wireless environments: channel estimation, system design and applications in 6G networks

Liang

Chen

Long

et al. 2021

Sci. China Inf. Sci.

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Reconfigurable intelligent surface (RIS), one of the key enablers for the sixth-generation (6G) mobile communication networks, is considered by designers to smartly reconfigure the wireless propagation environment in a controllable and programmable manner. Specifically, an RIS consists of a large number of low-cost and passive reflective elements (REs) without radio frequency chains. The system gain of RIS wireless systems can be achieved by adjusting the phase shifts and amplitudes of the REs so that the desired signals can be added constructively at the receiver. However, an RIS typically has limited signal processing capability and cannot perform active transmitting/receiving in general, which leads to new challenges in the physical layer design of RIS wireless systems. In this paper, we provide an overview of the RIS-aided wireless systems, including the reflection principle, channel estimation, and system design. In particular, two types of emerging RIS systems are considered: RIS-aided wireless communications (RAWC) and RISbased information transmission (RBIT), where the RIS plays the role of the reflector and the transmitter, respectively. We also envision the potential applications of RIS in 6G networks.

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Section: Deep Reinforcement Learning Based Methodsmentioning

confidence: 99%

Reconfigurable intelligent surfaces for smart wireless environments: channel estimation, system design and applications in 6G networks

Liang

Chen

Long

et al. 2021

Sci. China Inf. Sci.

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“…The system model of the DS-FTTD architecture at the m th carrier can be expressed as We consider that the CSI has been obtained, while the impact of imperfect CSI is numerically evaluated in Sec. V. In this work, we focus on the hybrid beamforming at transmitter, while one potential future extension is the use of reconfigurable intelligent surfaces (RIS) to manipulate the communication environment, which not only improves the coverage distance [46] but also reduces the complexity of beamforming at the transmitter [47].…”

Section: A Problem Formulation For Ds-fttd Hybrid Beamformingmentioning

confidence: 99%

Energy-efficient Dynamic-subarray with Fixed True-time-delay Design for Terahertz Wideband Hybrid Beamforming

Liu¹,

Chen²,

Yuan³

2022

Preprint

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Hybrid beamforming for Terahertz (THz) ultra-massive multiple-input multiple-output (UM-MIMO) systems is a promising technology for 6G space-air-ground integrated networks, which can overcome huge propagation loss and offer unprecedented data rates. With ultra-wide bandwidth and ultra-largescale antennas array in THz band, the beam squint becomes one of the critical problems which could reduce the array gain and degrade the data rate substantially. However, the traditional phase-shiftersbased hybrid beamforming architectures cannot tackle this issue due to the frequency-flat property of the phase shifters. In this paper, to combat the beam squint while keeping high energy efficiency, a novel dynamic-subarray with fixed true-time-delay (DS-FTTD) architecture is proposed. Compared to the existing studies which use the complicated adjustable TTDs, the DS-FTTD architecture has lower power consumption and hardware complexity, thanks to the low-cost FTTDs. Furthermore, a lowcomplexity row-decomposition (RD) algorithm is proposed to design hybrid beamforming matrices for the DS-FTTD architecture. Extensive simulation results show that, by using the RD algorithm, the DS-FTTD architecture achieves near-optimal array gain and significantly higher energy efficiency than the existing architectures. Moreover, the spectral efficiency of DS-FTTD architecture with the RD algorithm is robust to the imperfect channel state information.

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“…III-C) in a multi-hop network [248]. For example, simulation results illustrate the feasibility and advancement of multi-hop THz RIS assisted networks, compared to single-hop systems and those without RIS [249]. Specifically, the management of direction is supported by deep reinforcement learning (DRL) to achieve the optimization for NP-hard hybrid beamforming.…”

Section: Multi-hop Communications With Active and Passive Relaysmentioning

confidence: 99%

TeraHertz Band Communication: An Old Problem Revisited and Research Directions for the Next Decade

Akyildiz¹,

Han²,

Hu³

et al. 2021

Preprint

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TeraHertz (THz) band communications are envisioned as a key technology for 6G and Beyond. As a fundamental wireless infrastructure, THz communication can boost abundant promising applications. In 2014, our team published two comprehensive roadmaps for the development and progress of THz communication networks [1], [2], which helped the research community to start research on this subject afterwards. In particular, this topic became very important and appealing to the research community due to 6G wireless systems design and development in recent years. Many papers are getting published covering different aspects of wireless systems using the THz band. With this paper, our aim is looking back to the last decade and revisiting the old problems and pointing out what has been achieved in the research community so far. Furthermore, in this paper still to be investigated new research challenges for the THz band communication systems are presented by covering diverse subtopics such as from perspectives of devices, channel behavior, communication and networking problems, physical testbeds and demonstration systems. The key aspects presented in this paper will enable THz communications as a pillar of 6G and Beyond wireless systems in the next decade.

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Multi-Hop RIS-Empowered Terahertz Communications: A DRL-Based Hybrid Beamforming Design

Cited by 336 publications

References 56 publications

Reconfigurable intelligent surfaces for smart wireless environments: channel estimation, system design and applications in 6G networks

Reconfigurable intelligent surfaces for smart wireless environments: channel estimation, system design and applications in 6G networks

Energy-efficient Dynamic-subarray with Fixed True-time-delay Design for Terahertz Wideband Hybrid Beamforming

TeraHertz Band Communication: An Old Problem Revisited and Research Directions for the Next Decade

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