Secure reconfigurable intelligent surface aided heterogeneous VLC–RF cooperative NOMA networks

In this paper, we investigate the physical layer security for a reconfigurable intelligent surface (RIS)-aided heterogeneous visible light communication (VLC) and radio-frequency (RF) network with two legitimate user equipments (UEs) in cooperative nonorthogonal multiple access (NOMA). An external eavesdropper (Eve) tries to eavesdrop the information from the cooperative channel. Since VLC is mainly available for line-of-sight path, and the UEs and Eve under the worktable cannot directly receive signals from the optical access point, a device is naturally employed to perform optical–electrical conversion and RF transmission. Further the device and RIS are jointly employed to eliminate blind spots and extend communication coverage. With these settings, the statistical characteristics of the VLC link and RF link are determined based on the feature of the optical channel and the RIS-aided wireless channel, respectively. The close-form expression of the secrecy outage probability for the proposed RIS-aided heterogeneous VLC–RF cooperative NOMA network is derived. Simulation results show the secrecy outage performance of the proposed network depends on not only the reflecting meta-surface number of the RIS, the power allocation based on NOMA, but also the tradeoff design between the optical and electrical parameters. •Comprehensive secrecy performance analysis of an RIS-aided heterogeneous VLC–RF cooperative NOMA network is presented.•Statistical characteristics of the VLC link and the RF link are determined.•Close-form expression of secrecy outage probability for the proposed network is derived.•Tradeoff design between the optical and electrical parameters has great effect on the secrecy outage performance.•Proposed RIS-aided heterogeneous VLC–RF network performs better than VLC–RF multi-hop AF relay network in the secrecy outage probability.