[Paper Review] Securing Visible Light Communication Systems by Beamforming in the Presence of Randomly Distributed Eavesdroppers

Sung Hwan Cho, Gaojie Chen+1 more|arXiv (Cornell University)|Jul 21, 2017

Optical Wireless Communication Technologies21 references4 citations

TL;DR

This paper proposes an optimal beamforming scheme for visible light communication (VLC) systems with multiple LED transmitters and a single user equipment (UE), securing transmission against randomly distributed eavesdroppers (EDs) using only statistical knowledge of ED locations. By optimizing beamforming based on the intensity of the ED process and the intended channel, the scheme achieves superior secrecy performance compared to LED selection, with a closed-form approximation for secrecy outage probability (SOP) derived via secrecy capacity bounds.

ABSTRACT

This paper considers secrecy enhancement mechanisms in visible light communication (VLC) systems with spatially distributed passive eavesdroppers (EDs) under the assumption that there are multiple LED transmitters and one legitimate receiver (UE). Based on certain amplitude constraints, we propose an optimal beamforming scheme to optimize secrecy performance. Contrary to the case where null-steering is made possible by using knowledge of the ED locations, we show that the optimal solution when only statistical information about ED locations is available directs the transmission along a particular eigenmode related to the intensity of the ED process and the intended channel. Then, a sub-optimal LED selection scheme is provided to reduce the secrecy outage probability (SOP). An approximate closed-form for the SOP is derived by using secrecy capacity bounds. All analysis is numerically verified by Monte Carlo simulations. The analysis shows that the optimal beamformer yields superior performance to LED selection. However, LED selection is still a highly efficient suboptimal scheme due to the complexity associated with the use of multiple transmitters in the full beamforming approach. These performance trends and exact relations between system parameters can be used to develop a secure VLC system in the presence of randomly distributed EDs.

Motivation & Objective

• To enhance physical layer security in VLC systems where eavesdroppers are randomly distributed and their locations are unknown.
• To design a beamforming strategy that maximizes secrecy performance under amplitude constraints when only statistical information about eavesdropper distribution is available.
• To propose a suboptimal LED selection scheme that reduces secrecy outage probability (SOP) with lower complexity than full beamforming.
• To derive approximate closed-form expressions for SOP using secrecy capacity bounds under the LED selection scheme.
• To validate the theoretical analysis through Monte Carlo simulations and compare performance with benchmark schemes.

Proposed method

• The optimal beamformer is derived by maximizing secrecy performance metrics (e.g., SNR, secrecy capacity bounds) under amplitude constraints, using the dominant eigenmode associated with the intended channel and the statistical ED process intensity.
• The system models eavesdroppers as a homogeneous Poisson point process (PPP) on the work plane, enabling stochastic geometry-based analysis of the minimum distance to the nearest ED.
• The signal-to-noise ratio (SNR) at the UE is modeled as a function of distance using a path-loss model with exponent m+3, incorporating DC bias and LED power.
• The secrecy outage probability (SOP) is analyzed using bounds on secrecy capacity, and a closed-form approximation is derived by approximating the area function A(d) with piecewise linear functions.
• A suboptimal LED selection scheme is proposed, selecting the transmitter closest to the UE to reduce complexity while maintaining good secrecy performance.
• Monte Carlo simulations are used to numerically verify the analytical results and compare the performance of optimal beamforming and LED selection.

Experimental results

Research questions

• RQ1 How can physical layer security be enhanced in VLC systems when eavesdropper locations are unknown but their spatial intensity is known?
• RQ2 What is the optimal beamforming strategy that maximizes secrecy performance under amplitude constraints when only statistical information about eavesdropper distribution is available?
• RQ3 How does the performance of the optimal beamformer compare to a low-complexity LED selection scheme in terms of secrecy outage probability?
• RQ4 Can a closed-form approximation for the secrecy outage probability be derived under the LED selection scheme using secrecy capacity bounds?
• RQ5 What is the impact of system parameters such as LED intensity, user distance, and eavesdropper density on secrecy performance?

Key findings

• The optimal beamformer, derived from the dominant eigenmode of the intended channel and the ED process intensity, achieves superior secrecy performance compared to LED selection.
• The proposed LED selection scheme significantly reduces complexity while maintaining strong secrecy performance, especially when the UE is close to one of the LEDs.
• A closed-form approximation for the secrecy outage probability (SOP) is derived under LED selection, enabling efficient system design and parameter optimization.
• Monte Carlo simulations confirm that the optimal beamforming scheme outperforms LED selection in terms of secrecy outage probability, with the performance gap narrowing as the UE approaches a transmitter.
• The analytical SOP bounds are shown to closely match simulation results, validating the accuracy of the derived expressions.
• The study establishes that the optimal beamformer's performance is robust to uncertainty in eavesdropper locations, making it suitable for real-world VLC deployments in open indoor environments.