Pointing error evaluation in IRS-assisted VLC systems for indoor hospital environments: a comparative analytical study

Abstract

Visible light communication (VLC) has emerged as a promising technology for indoor wireless networks that offers immunity to electromagnetic interference and enhanced physical-layer security, properties that are particularly valuable in hospital and clinical environments. Intelligent reflecting surfaces (IRSs) have recently been proposed to extend VLC coverage by enabling non-line-of-sight (NLoS) transmission when direct optical paths are blocked by medical staff, equipment, or movable infrastructure. However, the cascaded transmitter–IRS–receiver geometry introduces compounded misalignment effects that are not present in conventional line-of-sight (LoS) links, and their analytical characterization remains an open problem. This study presents a unified analytical framework for quantifying and comparing pointing errors on conventional LoS and IRS-assisted VLC links in indoor hospital environments. Closed-form expressions are derived for the composite pointing-error variance, and the radial displacement is modeled using a Rayleigh distribution. Analytical expressions for the average received power, electrical signal-to-noise ratio (SNR), and outage probability are then obtained for both link configurations. The results indicate that IRS deployment results in an SNR degradation of approximately 3–5 dB under practical conditions, and the probability of outage increases significantly with the variance of the pointing error, underscoring the importance of precise beam alignment and robust IRS control for reliable hospital wireless connectivity.