Hybrid Dimming Scheme based on Transmit Antenna Selection and Precoding for MU MC VLC System

This paper proposes a hybrid dimming scheme based on joint design of transmit antenna selection and precoding (TASP-HD) for dimmable multi-cell multi-user multiple-input single-output visible light communications systems. In TASPHD, both the direct current bias and the number of activated light-emitting-diodes are dynamically adjusted to achieve efficient communications under the constraints of dimming level and illumination uniformity. With the goal of maximizing the sum-rate of users, a joint transmit antenna selection and precoding design problem is formulated. This problem is a non-convex, mixed integer problem, and thus it is non-deterministic polynomial time hard. To solve the problem, the original problem is seperated into two subproblems. The first subproblem is a mixed integer problem in terms of transmit antenna selection, which is solved by the branch-and-bound algorithm. With the obtained transmit antenna selection matrix, the second subproblem in terms of the precoding matrix is solved by the Lagrangian dual method. Finally, these two subproblems are iteratively solved to obtain a convergent solution. The simulation results verify that the proposed TASP-HD can achieve 6 dB signal-to-noise ratio gains over the analog dimming scheme when the dimming level is 70% for a target bit error rate of $10^{-3}$.