In the design of reconfigurable intelligent surfaces (RISs)-aided visible light communication (VLC) systems, most studies have focused on the deployment of mirror arrays and metasurfaces on walls to influence signal propagation and enhance communication performance. This paper provides a new research direction in the design and performance optimization of RIS-aided VLC systems whereby voltage-controlled tunable liquid crystals (LCs) are deployed as part of the VLC receiver. The purpose of the LC RIS is to provide incident light steering and intensity amplification in order to improve the received signal strength and the corresponding achievable data rate. More specifically, an LC RIS-based VLC receiver design is proposed and its operating principles and the channel model for a VLC system with such a receiver are provided. Since the refractive index of the LC RIS plays a critical role in the wave-guiding and light amplification capabilities of this novel receiver, a rate maximization problem is considered to achieve the optimal refractive index and the required voltage to obtain the best light amplification and data rate performances. This communication design problem is a non-convex optimization problem for which a metaheuristic approach is developed based on the sine-cosine algorithm. Simulation results are used to confirm the considerable data rate improvement by the proposed LC RIS-based VLC receiver and optimization algorithm when compared to a VLC receiver without the LC RIS and a baseline scheme, respectively.
This letter studies the energy efficiency (EE) 1 optimization of cooperative visible light communication (VLC) 2 systems while considering the inter-cell interference and the line-3 of-sight blockage problems. Specifically, the optimization problem 4 of subchannel and power allocation to maximize EE under 5 transmit power budgets and users' minimum rate constraints is 6 considered. The formulated problem turns out to be a difficult 7 nonlinear fractional program for which a low-complexity 8 iterative solution based on fractional programming theory 9 and the quadratic transform approach is proposed. Extensive 10 simulations are conducted to show the efficacy of the proposed 11 scheme over conventional approaches. In addition, the outage 12 analysis and impacts of varying the transmit power and the 13 subchannel bandwidth on the EE performance are investigated.
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