  Channel capacity bounds are derived for a point-to-point indoor visible light
communications (VLC) system with signal-dependent Gaussian noise. Considering
both illumination and communication, the non-negative input of VLC is
constrained by peak and average optical intensity constraints. Two scenarios
are taken into account: one scenario has both average and peak optical
intensity constraints, and the other scenario has only average optical
intensity constraint. For both two scenarios, we derive closed-from expressions
of capacity lower and upper bounds. Specifically, the capacity lower bound is
derived by using the variational method and the property that the output
entropy is invariably larger than the input entropy. The capacity upper bound
is obtained by utilizing the dual expression of capacity and the principle of
"capacity-achieving source distributions that escape to infinity". Moreover,
the asymptotic analysis shows that the asymptotic performance gap between the
capacity lower and upper bounds approaches zero. Finally, all derived capacity
bounds are confirmed using numerical results.
