This paper proposes a novel zero-forcing (ZF) beamforming strategy that can simultaneously cope with active and passive eavesdroppers (EDs) in visible light communication systems. A related optimization problem is formulated to maximize the signal-to-noise ratio (SNR) of the legitimate user (UE) while suppressing the SNR of active ED to zero and constraining the average SNR of passive EDs. The proposed beamforming directs the transmission along a particular eigenmode related to the null space of the active ED channel and the intensity of the passive ED point process. An inverse free preconditioned Krylov subspace projection method is used to find the eigenmode. The numerical results show that the proposed ZF beamforming scheme yields better performance relative to a traditional ZF beamforming scheme in the sense of increasing the SNR of the UE and reducing the secrecy outage probability.
This paper proposes a novel zero-forcing (ZF) beamforming strategy that can simultaneously cope with active and passive eavesdroppers (EDs) in visible light communication systems. A related optimization problem is formulated to maximize the signal-to-noise ratio (SNR) of the legitimate user (UE) while suppressing the SNR of active ED to zero and constraining the average SNR of passive EDs. The proposed beamforming directs the transmission along a particular eigenmode related to the null space of the active ED channel and the intensity of the passive ED point process. An inverse free preconditioned Krylov subspace projection method is used to find the eigenmode. The numerical results show that the proposed ZF beamforming scheme yields better performance relative to a traditional ZF beamforming scheme in the sense of increasing the SNR of the UE and reducing the secrecy outage probability.
This article proposes zero-forcing (ZF) beamforming strategies that can simultaneously deal with active and passive eavesdroppers in visible light communication (VLC) systems. First, we propose a ZF beamforming scheme that steers a transmission beam to the null space of active eavesdroppers' (AEDs) channel, while simultaneously considering the SNRs for a legitimate user (UE) and passive eavesdroppers (PEDs) residing at unknown locations. To find an eigenmode related to the optimal beamforming vector, we adopt an inverse free preconditioned Krylov subspace projection method. For unfavorable VLC secrecy environments, the proposed ZF beamformer appears to be incapable of effectively coping with the PEDs due to the strict condition that the data transmission must be in the null space of the AEDs' channel matrix. Hence, an alternative beamforming scheme is proposed by relaxing the constraint on the SNRs of the AEDs. The related optimization problem is formulated to reduce the secrecy outages caused by PEDs, while simultaneously satisfying the target constraints on the SNRs of the UE and the AEDs. To simplify the mathematical complexity of the approach, Lloyd's algorithm is employed to sample the SNR field, which in turn discretizes the problem, thus making it tractable for practical implementation. The numerical results show that both the exact and relaxed ZF beamforming methods achieve superior performance in the sense of secrecy outage relative to a benchmark ZF scheme. Moreover, the proposed relaxed ZF beamforming method is shown to cope with PEDs better than the exact ZF beamforming approach for unfavorable VLC environments.
This paper proposes a novel cooperative beamforming and jamming scheme to deal with passive and active eavesdroppers (EDs) in indoor visible light communication (VLC) networks. An ED in VLC systems can augment its front-end receiver by implementing possible device modifications; thus, jamming is very useful for curbing such an enhanced ED since it would be impossible to distinguish between the information and jamming signals. In contrast to the traditional artificial noise strategies for VLC that can only deal with either passive or active EDs, we propose a combined scheme of beamforming and jamming that significantly improves secrecy performance when both types of EDs exist. The proposed scheme is designed to maximize the signal-to-interference-plus-noise ratio (SINR) of the legitimate receiver, entirely suppress the SINRs of the active EDs, and restrict the average SINR of the passive EDs. We apply an inverse free preconditioned Krylov subspace projection method and the convex-concave procedure to obtain the suboptimal beamforming weight and jamming intensity vectors. Also, an optimal power splitter coefficient is found through the golden section search method. The numerical results verify that the proposed scheme shows superior performance compared to the three benchmarks: 1) zero-forcing beamforming; 2) artificial noise scheme; and 3) enhanced zero-forcing beamforming.
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 user equipment. Based on certain amplitude constraints, we propose a beamforming scheme to improve secrecy performance. Contrary to the case where null-steering is made possible by using knowledge of the ED locations, the proposed beamforming 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 LED selection scheme that is less complicated than beamforming is provided to reduce the secrecy outage probability (SOP). An approximate closed-form for the SOP is derived by using secrecy rate bounds. All the analysis is numerically verified by Monte-Carlo simulations. The analysis shows that the beamformer yields superior performance to LED selection. However, LED selection is still a highly efficient alternative 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.
Recent developments in visible light communications (VLC) have focused on enhancing its security and privacy. This paper studies the physical layer security in VLC networks with multiple users when there is a single wiretap eavesdropper. In particular, our aim is to design the optimal artificial noise (AN)-aided precoding scheme to improve the secrecy performance in terms of legitimate users and eavesdropper’s signal-to-interference-plus-noise ratios (SINRs). The purpose of our AN-aided precoding design is to ensure a fairness of the legitimate users’ SINRs while impairing the quality of eavesdropper’s channel as much as possible. Depending on the availability of the eavesdropper’s channel state information (CSI) at the transmitters, there are generally two design strategies. When the eavesdropper’s CSI is unknown to the transmitters (i.e., passive eavesdropper), the AN is constructed to be orthogonal to the users’ aggregate channel matrix. In case the eavesdropper’s CSI is available (i.e., active eavesdropper), the AN design strategy is to keep the SINR of the eavesdropper below a certain predefined threshold. Aside from the general design, we also study a specific design with the zero-forcing (ZF) technique and compare its performance with that of the general design. In both designs, numerical results show that significant gaps between users’ and eavesdropper’s SINR can always be achieved, thus guaranteeing a high secrecy performance. It is also observed that while the general design outperforms the ZF one in terms of the users’ SINRs, it does not result in lower eavesdropper’s SINRs compared to the ZF design, especially in the low transmit power region.
In this paper, we address the secure data transmission through visible light communication (VLC) using physical layer security (PLS) techniques and particularly, optical beamforming with the zero-forcing algorithm. More precisely, we consider the secrecy capacity of classical multiple-input single-output VLC so that the system can deal with eavesdroppers by minimizing the secrecy outage probability (SOP). The considered wireless channel is modeled by the Gaussian distribution, which is subject to amplitude constraints. We quantity the achievable secrecy capacity and SOP for the conventional line-of-sight VLC link and show that how the beamforming can determine the optimal placement of the transmitters. We also show that for a given SOP, the proposed optimal placement offers a signal-to-noise ratio gain of up to 6 dB compared to classical methods such as uniform placement of the transmitters. Our numerical results indicate that the proposed optimal LED arrangement can achieve an SOP of 10−10 while the SOP with uniform arrangement is equal to 10−4.
Recently, the hybrid radio frequency (RF)/ visible light communication (VLC) network has been widely studied due to the advantages of high data transmission and no interference between the two networks. Taking the physical layer security (PLS) into account, most work on hybrid RF/VLC network focused on single user. However, many practical scenarios require hybrid network to serve multiple users (MU). Thus, in this paper, we make a study on the PLS of MU hybrid RF/VLC network where the messages to each of the users must be kept confidential from the other and also from the external eavesdropper. To enhance the secrecy performance of the hybrid network, we propose a zero forcing (ZF) beamforming strategy to ensure that the information of each legitimate user can not be received by other users and the eavesdropper. A sum secrecy rate (SSR) optimization problem is formulated under the ZF constraint and the constraint of the power transmitted from the VLC and the RF access point. To reduce the complexity of the original problem, we decouple it into two successive sub-problems and solve them via convex optimization theory and matrix theory. Simulation results show that a positive SSR can always be achieved, and the SSR of the MU hybrid RF/VLC network is superior to that of the standalone RF and VLC networks.