Terahertz Massive MIMO With Holographic Reconfigurable Intelligent Surfaces
Ziwei Wana b, Zhen Gaoa b, Feifei Gaoc d e, Marco Di Renzof, Mohamed‐Slim Alouinig
- aAdvanced Research Institute of Multidisciplinary Science, Beijing Institute of Technology, Beijing, China
- bSchool of Information and Electronics, Beijing Institute of Technology, Beijing, China
- cDepartment of Automation, Beijing National Research Center for Information Science and Technology (BNRist), Tsinghua University, Beijing, China
- dInstitute for Artificial Intelligence, Tsinghua University (THUAI), Beijing, China
- eState Key Laboratory of Intelligent Technologies and Systems, Tsinghua University, Beijing, China
- fUniversité Paris-Saclay, CNRS, CentraleSupélec, Laboratoire des Signaux et Systèmes, 3 Rue Joliot-Curie, Gif-sur-Yvette, France
- gComputer, Electrical, and Mathematical Science and Engineering Division, King Abdullah University of Science and Technology (KAUST), Thuwal, Saudi Arabia
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Abstract
We propose a holographic version of a reconfigurable intelligent surface (RIS) and investigate its application to terahertz (THz) massive multiple-input multiple-output systems. Capitalizing on the miniaturization of THz electronic components, RISs can be implemented by densely packing sub-wavelength unit cells, so as to realize continuous or quasi-continuous apertures and to enable holographic communications. In this paper, in particular, we derive the beam pattern of a holographic RIS. Our analysis reveals that the beam pattern of an ideal holographic RIS can be well approximated by that of an ultra-dense RIS, which has a more practical hardware architecture. In addition, we propose a closed-loop channel estimation (CE) scheme to effectively estimate the broadband channels that characterize THz massive MIMO systems aided by holographic RISs. The proposed CE scheme includes a downlink coarse CE stage and an uplink finer-grained CE stage. The uplink pilot signals are judiciously designed for obtaining good CE performance. Moreover, to reduce the pilot overhead, we introduce a compressive sensing-based CE algorithm, which exploits the dual sparsity of THz MIMO channels in both the angular domain and delay domain. Simulation results demonstrate the superiority of holographic RISs over the non-holographic ones, and the effectiveness of the proposed CE scheme.