  In this paper, we investigate the secrecy performance of a single-input
single-output visible light communication (VLC) channel in the presence of an
eavesdropper. The studied VLC system comprises distributed light-emitting
diodes (LEDs) and multiple randomly located users (UEs) within an indoor
environment. A sum secrecy rate maximization problem is formulated to enhance
confidential transmission by selecting the optimal LED for each UE. To address
the non-convex and non-continuous nature of this problem, we propose a tabu
search-based algorithm that prevents entrapment in local optima by organizing
the trial vectors from previous iterations. Furthermore, we develop three
straightforward LED selection strategies that reduce computational complexity
by employing fixed criteria to choose one LED for each UE. We also examine the
convergence and complexity analysis of the proposed algorithm and strategies.
The results demonstrate that the secrecy performance of our proposed algorithm
is very close to the global optimal value and surpasses that of the developed
strategies.
