Relay-Aided Secure Broadcasting for Visible Light Communications

TL;DR

This paper investigates secure visible light communication broadcast channels with multiple relays, deriving achievable secrecy rates and proposing relaying schemes with secure beamforming to enhance security against eavesdroppers.

Contribution

It introduces novel relaying schemes with secure beamforming for VLC broadcast channels, deriving secrecy rate regions under amplitude constraints, and compares their effectiveness.

Findings

Relaying schemes outperform direct transmission in secrecy rates.

Secure beamforming effectively reduces eavesdropper's information.

Optimal relaying scheme depends on eavesdropper's position and relay layout.

Abstract

A visible light communication broadcast channel is considered, in which a transmitter luminaire communicates with two legitimate receivers in the presence of an external eavesdropper. A number of trusted cooperative half-duplex relay luminaires are deployed to aid with securing the transmitted data. Transmitters are equipped with single light fixtures, containing multiple light emitting diodes, and receiving nodes are equipped with single photo-detectors, rendering the considered setting as a single-input single-output system. Transmission is amplitude-constrained to maintain operation within the light emitting diodes' dynamic range. Achievable secrecy rate regions are derived under such amplitude constraints for this multi-receiver wiretap channel, first for direct transmission without the relays, and then for multiple relaying schemes: cooperative jamming, decode-and-forward, and amplify-and-forward. Superposition coding with uniform signaling is used at the transmitter and the relays. Further, for each relaying scheme, secure beamforming vectors are carefully designed at the relay nodes in order to hurt the eavesdropper and/or benefit the legitimate receivers. Superiority of the proposed relaying schemes, with secure beamforming, is shown over direct transmission. It is also shown that the best relaying scheme depends on how far the eavesdropper is located from the transmitter and the relays, the number of relays, and their geometric layout.