Digital Twin Enabled 6G Cell-Free Multi-Function Reconfigurable Metasurfaces Communications: Concepts, Challenges, and Future Directions

Cell-free massive multiple-input multiple-output (CF-mMIMO) and multi-function reconfigurable metasurfaces are two potential technologies for coping with 6G demands. Their coexistence, also called cell-free reconfigurable metasurfaces (CFRM) communications, contribute to enhancing wireless network performances in an energy-and-hardware-efficient manner but shows great voracious appetite for data, optimization and resources. Digital twin (DT) provides a hotbed for the development of CFRM communications. This article aims to present how DT and CFRM communications are organically merged as an integrated whole, which enable 6G deployment from a perspective of three typical cases, including intelligent reconfigurable holographic surface (RHS)/reconfigurable intelligent surface (RIS) deployment optimization, hybrid beamforming optimization and intelligent model/resource orchestration. A real-world DT enabled CFRM communications application is presented, and simulation results have demonstrated that DT enabled CFRM can provide remarkable evaluate the implementation platform for subarray reconfigurable metasurfaces based on reinforcement learning to improve the energy efficiency of CFRM. Finally, we conclude the article with potential challenges of RHS/RISs and several future research topics.