Enhanced secrecy outage probability for multiple-input single-output-VLC systems through optical beamforming and improved light emitting diodes deployment

Abstract

The authors propose to arrange the light emitting diodes (LEDs) on the ceiling for an indoor visible light communication system in order to minimise the secrecy outage probability (SOP) at the location of the legitimate user (LU). More precisely, by deriving the secrecy capacity for a multiple-input single-output-VLC system, we evaluate the SOP at the LU's location which is used as the appropriate metric to determine the position of the LEDs on the ceiling. To mitigate the effect of the eavesdropper, we derive the optimal beamforming coefficients which are used at the transmitter LED array with the aim of maximising the signal-to-noise ratio at the LU. Simulation results show that for a SOP of 10⁻⁴, the proposed SOP-based LED arrangement with optimal beamforming offers up to 3 dB gain in transmit power compared to the classical uniform LED arrangement with sub-optimal zero-forcing beamforming. Moreover, they show that by using the proposed method, the SOP is kept below a desired threshold, over a wider area inside the indoor environment compared to classical methods.