  In this paper, an improved channel model of visible light communication (VLC)
for ranging in presented. For indoor channel model of VLC, distance is
estimated based on received signal strength. In this model, received shot noise
as a distance-dependent parameter is considered in range estimation accuracy.
Moreover, based on this model, the Cramer-Rao lower bound is computed as the
theoretical limits on the performance and accuracy of any unbiased estimator.
In this way, the effects of horizontal and vertical distances are investigated.
In addition, the transmitted power effect on RSN and accordingly on CRLB is
demonstrated.
