Leveraging IRS Induced Time Delay for Enhanced Physical Layer Security in VLC Systems

Indoor visible light communication (VLC) is considered secure against attackers outside the confined area where the light propagates, but it is still susceptible to interception from eavesdroppers inside the coverage area. A new technology, intelligent reflecting surfaces (IRS), has been recently introduced, offering a way to control and steer light propagation in VLC systems. This letter proposes an innovative approach for enhancing the physical layer security (PLS) in IRS-assisted VLC by utilising the effect of the time delay induced by the IRS reflections. More specifically, we consider how to allocate the IRS elements in a way that produces destructive intersymbol interference at the eavesdropper's location while enhancing the signal reception at the legitimate user. Our results show that, at a fixed light-emitting diode power of 3W, the secrecy capacity can be enhanced by up to 253% at random positions for the legitimate user when the eavesdropper is located within a 1-meter radius of the LED. We show that careful IRS allocation can lead to enhanced PLS even when the eavesdropper has a more favorable position than the legitimate user.