Securing Visible Light Communication Systems by Beamforming in the Presence of Randomly Distributed Eavesdroppers

摘要

This paper considers secrecy enhancement mechanisms in visible lightcommunication (VLC) systems with spatially distributed passive eavesdroppers(EDs) under the assumption that there are multiple LED transmitters and onelegitimate receiver (UE). Based on certain amplitude constraints, we propose anoptimal beamforming scheme to optimize secrecy performance. Contrary to thecase where null-steering is made possible by using knowledge of the EDlocations, we show that the optimal solution when only statistical informationabout ED locations is available directs the transmission along a particulareigenmode related to the intensity of the ED process and the intended channel.Then, a sub-optimal LED selection scheme is provided to reduce the secrecyoutage probability (SOP). An approximate closed-form for the SOP is derived byusing secrecy capacity bounds. All analysis is numerically verified by MonteCarlo simulations. The analysis shows that the optimal beamformer yieldssuperior performance to LED selection. However, LED selection is still a highlyefficient suboptimal scheme due to the complexity associated with the use ofmultiple transmitters in the full beamforming approach. These performancetrends and exact relations between system parameters can be used to develop asecure VLC system in the presence of randomly distributed EDs.