Secure Cooperative Hybrid VLC-RF Systems

In this paper, a cooperative hybrid visible light communication (VLC)-radio frequency (RF) system with spatially random terminals is considered. Especially, a source node ( $S$ ) with a group of light-emitting diode (LED) lamps transmits information bits to a destination ( $D$ ), which is located out of $S$ ’s coverage area, via a relay node ( $R$ ). $R$ is equipped with a photodetector and an antenna to set up a VLC link between $S$ and $R$ , and a radio frequency (RF) link between $R$ and $D$ , respectively. Meanwhile, an eavesdropper ( $E$ ) equipped with a photodetector and an antenna tries to overhear the information delivery over VLC and RF links. Also, diversity receiving scheme is considered at $E$ , while the same modulation scheme is considered over both VLC and RF links. Furthermore, decode-and-forward scheme is adopted at $R$ to process and forward the received VLC signals. By employing stochastic geometry, we first characterize the probability density function and cumulative distribution function of the received signal-to-noise-ratio over both VLC and RF links, while considering the randomness of the locations of both $R$ , $E$ , and $D$ . Then, the secrecy performance of the target system is studied by deriving the approximated expressions for the secrecy outage probability under various cases. Finally, the proposed analytical models are verified via Monte-Carlo simulations.