Optimal Control for Digital-Twin THz/VLC Communication Networks

In this paper, the problem of delay minimization is investigated for digital-twin communication networks with both terahertz (THz) and visible light communication (VLC). In the studied framework, one macro base station (BS) transmits virtual reality (VR) images to small base stations (SBSs) and SBSs transmit images to users over THz link. The VLC positioning system provides accurate positions of indoor VR users to the outside BS, so that the BS can generate corresponding VR images. The problem is formulated as an optimization task aiming to minimize the total serving time for all users through appropriate VLC access points (VAP)s' selections, SBSs' selections and user association. The formulated problem is evidenced to be nonlinear and NP-complete, which is difficult to solve. To handle the difficulty, the problem is equivalently transformed into a mixed linear integer program, where the Big-M method is introduced. Simulation results reveal that the proposed method can reduce up to 33.2 % transmission delay compared with conventional methods.