Relay-Aided Physical Layer Security in Multi-Eavesdropper VLC via Optimization of Beamforming Vector and Spatial Position

We propose a novel relay-aided physical layer security scheme for multi-eavesdropper visible light communication. When eavesdroppers outnumber relays, we strategically position relays to prioritize blocking line-of-sight (LoS) paths from the light source to the subset of eavesdroppers with stronger interception capabilities, ingeniously transforming potential limitations of obstacles into security advantages. Subsequently, relays are designed to broadcast jamming signals, with beamforming vector optimized to minimize the sum signal-to-interference-plus-noise-ratio at remaining eavesdroppers. Conversely, we solely determine relay placement to obstruct all LoS paths from the light source to eavesdroppers. Numerical results demonstrate that our scheme significantly outperforms traditional schemes in security capacity.