Relay-Aided Based Physical Layer Security in VLC System With Improved Noise Model

A visible light communication (VLC) system with an improved noise model applied to physical layer security (PLS) is investigated, where secure beamforming signals with superposition coding are used. In the improved model, the output signal follows Gaussian distribution, but its variance is signal-dependent. Two different methods are proposed to obtain lower and upper bounds on the secrecy rate of the strong user for direct transmission. Under some constraints, closed-form expressions of the lower and upper bounds on secrecy rate regions for various (trusted cooperative half-duplex) relaying schemes are derived. Moreover, the scenarios of blockage/outside coverage are included, and the relevant security performances are discussed. Numerical results show that the lower and upper bounds on secrecy rate regions are tight enough, and the cooperative jamming is superior over other relaying schemes.