  In this work, we investigate the transmission sum rate as well as the secrecy
sum rate of indoor visible light communication (VLC) networks for mobile
devices with the power domain non-orthogonal multiple access (NOMA)
transmission, where multiple legitimate users are equipped with photodiodes
(PDs). We introduce a body blockage model of the legitimate users as well as
the eavesdropper to focus on the case where the communications from
transmitting light-emitting diodes (LEDs) to receiving devices are blocked by
the bodies of receiving users. Furthermore, in order to improve the secrecy
without any knowledge of the channel state information (CSI) of the
eavesdropper, a novel LED arrangement is introduced to reduce the overlapping
area covered by LED units supporting different users. We also propose two LED
operation strategies, called simple and smart LED linking, and evaluate their
performance against the conventional broadcasting in terms of transmission sum
rate and secrecy sum rate. Through computer simulations, the superiority of our
proposed strategies is demonstrated.
