Aug 2026· International Symposium on Wireless Communication Systems· pp. 1-6· 0 citations· 11 references
Abstract
Stacked Intelligent Metasurfaces (SIMs) are promising for next-generation multi-input multi-output (MIMO) systems, as they can realize low-cost and energy-efficient wavedomain transformations. However, SIM-assisted MIMO systems face challenging channel estimation and beamforming optimization, since passive SIM elements lack signal processing capability and the resulting precoding problem is highly non-convex. To tackle these challenges, we exploit the time-division duplex (TDD) channel reciprocity to perform over-the-air gradient backpropagation, and propose a physical projected gradient descent (P2GD) framework. The proposed method jointly handles channel acquisition and beamforming without requiring explicit channel state information, while optimizing the achievable sum rate under zero-forcing (ZF) constraints. Simulation results show that P2GD achieves effective multi-user beamforming with significantly reduced channel estimation overhead, providing a practical low-cost solution for SIM-assisted systems.
Tri-hybrid multiple-input multiple-output architectures have recently emerged as a promising enabler for next-generation wireless systems, as they potentially provide enhanced design flexibility without a proportional increase in hardware cost or power consumption. However, the resulting triple-domain coupling renders...
Pin-Jun Zheng, Md. Jahangir Hossain, Anas Chaaban· IEEE Transactions on Signal...· 1 citation
This letter investigates robust multiuser downlink beamforming for a base-station-side stacked intelligent metasurface (SIM) with finite-resolution phase control and imperfect channel state information. Because the effective channel depends on the SIM configuration, we estimate the SIM-output-to-user channel from multi...
Shabih Ul Hassan, Jian-Cheng An, Fahim Niaz et al.· IEEE Wireless Communications...· 1 citation
In this paper, we investigate beamforming for a wideband terahertz (THz) communication system serving multiple users in the near-field region. A hybrid beamforming architecture employing fixed true time delays (FTTDs) and phase shifters (PSs) is introduced to reduce the spatial wideband effect. Both fully-connected (FC...
Wen-Qiang Chu, Qiu-Yan Liu, Yan-Xia Cao et al.· IEEE Transactions on Wireles...· 0 citations
A circuit-based metasurface is proposed for multiuser orthogonal beamforming and multiple-input-multiple-output (MIMO) wireless communications. The metasurface consists of several pairs of propagation and phased shifter layers, stacked several times to form an electrically thin structure that provides the necessary non...
Feiyu Shan, Hao Luo, Ahmed Alkhateeb et al.· Metamaterials· 0 citations
The phenomena of distance-dependent degrees of freedom (DoFs) and spherical wavefronts in the near-field region open new avenues for the development of integrated sensing and communication (ISAC). However, most existing works that employ hybrid beamforming architectures lack the flexibility to accommodate spatially var...
Yi-Fei Zhao, Yong Zhou, Hong-Lin Hu et al.· IEEE Transactions on Communi...· 0 citations
This paper studies continuous transmissive reconfigurable intelligent surface (CT-RIS)-enabled multiuser downlink communications, where passive beamforming is characterized by a phase function defined over the continuous aperture. We employ a distance-dependent spherical-wave model for the base station (BS)-to-CT-RIS l...
Bei-Ning Han, Shu-Meng Zhang, De-You Zhang et al.· 0 citations
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