Enhancing Secrecy Rates in Indoor Visible Light Communication via Spatially Confined Data Transmission and Artificial Noise Under Multipath Reflections

Visible light communication (VLC) is inherently a broadcast medium, since any receiver inside the illuminated volume can capture the transmitted signal. Physical layer security exploits the asymmetry between the legitimate and eavesdropping channels, yet lighting design pursues a uniform illumination that suppresses exactly this asymmetry. This paper quantifies the resulting trade-off for three luminaire layouts, namely four symmetric clusters, a single central cluster and a distributed grid, in a 5 m × 5 m × 3 m room, under an amplitude-constrained Gaussian wiretap model and a lower bound on the secrecy capacity. Unlike most prior studies, the channel model includes diffuse multipath reflections, obtained from an interreflection matrix truncated at the third order. Three schemes are compared, namely common SISO broadcasting, spatially confined data transmission (SCDT) and SCDT with artificial noise (SCDT-AN). Uniform illumination yields the lowest secrecy under SISO, whereas SCDT and SCDT-AN create the required asymmetry through the transmission itself. At the best receiver location with a 20° half-power semi-angle and reflections included, the average secrecy rate of the four-cluster layout rises from 2.10 to 5.36 and 5.68 bit per channel use. It is found that although reflections reduce the SISO rate at every position, SCDT can overcome the residual reflected lights with a nearly unchanged rate, and SCDT-AN further improves it.