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IEEE Wireless Communications Letters

Secure Beamforming for MISO Visible Light Communications With ISI and NLoS Components

Jin‐Yuan Wang, Yin-Chang Yu, Ding-Shan Lu, Dao-Peng Su

Published Jan 8, 2024• 8 citations
Publisher

Abstract

For simplicity, most works on visible light communications (VLC) neglect the non-line-of-sight (NLoS) channel gain and the inter-symbol interference (ISI). This letter investigates the optimal and robust secure beamforming problems for multiple-input single-output VLC systems, where both the NLoS channel gain and ISI are considered. Under perfect channel state information (CSI), we formulate an optimal beamforming problem to maximize the secrecy rate under amplitude constraints on beamformers. The problem is shown to be nonconvex. We transform it into multiple tractable quasiconvex subproblems, and propose an iterative algorithm to solve it. To be more practical, we then consider the imperfect CSI and design the robust secure beamformers. Numerical results verify the efficiency of the proposed beamforming schemes. Moreover, it is also shown that the NLoS channel gain can improve the secrecy rate and well-designed beamformers can reverse the effect of ISI.

DOI
10.1109/lwc.2024.3350544

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For simplicity, most works on visible light communications (VLC) neglect the non-line-of-sight (NLoS) channel gain and the inter-symbol interference (ISI). This letter investigates the optimal and robust secure beamforming problems for multiple-input single-output VLC systems, where both the NLoS channel gain and ISI are considered. Under perfect channel state information (CSI), we formulate an optimal beamforming problem to maximize the secrecy rate under amplitude constraints on beamformers. The problem is shown to be nonconvex. We transform it into multiple tractable quasiconvex subproblems, and propose an iterative algorithm to solve it. To be more practical, we then consider the imperfect CSI and design the robust secure beamformers. Numerical results verify the efficiency of the proposed beamforming schemes. Moreover, it is also shown that the NLoS channel gain can improve the secrecy rate and well-designed beamformers can reverse the effect of ISI.
This work considers secure downlink transmission in indoor multiple-input, single-output visible-light communication (VLC) links. In particular, we study the design of transmit beamformers that maximize the achievable secrecy rate subject to amplitude constraints imposed by the limited dynamic range of the light-emitting diodes (LEDs). Such constraints render the design problem nonconvex and difficult to solve. We show, however, that this nonconvex problem can be transformed into a solvable quasiconvex line search problem. We also consider the more realistic case of imperfect channel information regarding the receiver's and eavesdropper's links. We tackle the worst-case secrecy rate maximization problem, again subject to amplitude constraints. In our treatment, uncertainty in the receiver's channel is due to limited feedback, and is modeled by spherical sets. On the other hand, there is no feedback from the eavesdropper, and the transmitter shall utilize the line-of-sight channel gain equation to map the eavesdropper's nominal location and orientation into an estimate of the channel gain. Thus, we derive uncertainty sets based on inaccurate information regarding the eavesdropper's location and orientation, as well as the emission pattern of the LEDs. We also consider channel mismatches caused by the uncertain non-line-of-sight components. We provide numerical examples to demonstrate the performance gain of the optimal beamformer compared with the suboptimal schemes, and the robust beamformer compared with its nonrobust counterparts. We also evaluate the worst-case secrecy rate performance of the robust beamformer in a typical VLC scenario along with the aforementioned uncertainty sources.
To improve the performance of physical-layer security, secure beamforming schemes were designed for artificial noise (AN)-aided multiple-input single-output visible light communication (VLC) systems. To address the issue that non-line-of-sight (NLoS) channel gains were easily overlooked, a system model that simultaneously considers line-of-sight and NLoS channel gains was established. Under perfect and imperfect channel state information conditions, optimal and robust secure beamforming problems were formulated, respectively. Considering the limitations of semidefinite relaxation (SDR) and Gaussian randomization methods, secure beamforming schemes combining semidefinite programming and penalty function were proposed. Numerical results show that, compared with SDR and Gaussian randomization methods, the proposed schemes can provide at least 3 dB of power gain. Moreover, both the adoption of AN technology and the consideration of NLoS channel gain can effectively reduce the system’s transmission power.
In this paper, the physical-layer secrecy problem is investigated for the indoor multiple-input single-output (MISO) visible light communication systems. First, when the channel state information (CSI) of eavesdroppers is perfect, two kinds of optimal secure beamformers are, respectively, designed to minimize the transmit power and to maximize the secrecy rate. Moreover, it is shown that the secrecy rate maximization problem can be decomposed into a sequence of convex feasibility problems, which can be efficiently solved by using interior point methods. Second, when the CSI of eavesdroppers is imperfect, an ellipsoidal region model is applied to characterize the CSI uncertainty. This model leads to an infinite number of complicated constraints for the design of robust secure beamformers. By using theS\mathcal {S}S-lemma and semidefinite relaxation, this nonconvex problem is transformed into the convex semidefinite program. Finally, numerical results demonstrate the optimality and robustness of the proposed methods.
Visible light communication (VLC) is a promising technology for next-generation indoor wireless broadband communication systems. Physical layer security (PLS) is one proposed method to ensure data security for VLC in public areas. However, most PLS studies in the literature neglect the reflections in the VLC channel and do not consider inter-symbol interference (ISI). This paper investigates the ISI effects on the secrecy rate in multiple-input single-output VLC systems where the reflections are not neglected for the cases of perfect and imperfect knowledge of the eavesdropper’s channel state information. We aim to compensate for the ISI effects by designing zero-forcing (ZF) and artificial noise (AN) beamformers. In addition, we formulate optimization problems to maximize the secrecy rate resulting in non-convex and NP-hard problems. Thus, we utilize the particle swarm optimization algorithm for solutions and also convert non-convex optimization problems into easily solvable linear problems. Furthermore, robust ZF and AN beamformers for the worst-case scenario are considered for the cases of ISI and no ISI. The results reveal that ISI severely degrades the secrecy rate; however, well-designed beamformers can reverse the ISI effects.
This paper analyzes the secrecy rate and designs the secure beamforming for an indoor visible light communication (VLC) network consisting of one transmitter, one legitimate receiver, one eavesdropper, and several friendly jammers. In the VLC network, both the main and wiretapping channels have a uniformly distributed signal input and corrupted with additive white Gaussian noise. The imperfect channel state information (CSI) is considered by using the ellipsoidal approximation method. Under the amplitude constraints of the data and the interfering signal, the secrecy rate for the VLC network is analyzed. A beamforming optimization problem is proposed to maximize the secrecy rate with the given constraints. It is shown that the optimization problem is non-convex. In this paper, it is transformed into a solvable quasi-convex linear search problem. Numerical results demonstrate the performance gain of the optimal beamformer compared to the zero-forcing scheme. Moreover, the secrecy performance under different CSI uncertainties is also provided.
Securing visible light communication (VLC) systems with physical-layer technologies has drawn increasing attention. In this paper, we leverage both transmit beamforming and jamming techniques to enhance communication secrecy for a multiple-input single-output (MISO) VLC system with presence of multiple eavesdroppers. The transmit beamformer and jamming precoder are jointly optimized in the sense that the signal-to-noise ratio (SNR) of the legitimate user is maximized subject to maximum SNR constraints imposed on eavesdroppers, as well as light-emitting diode (LED) optical power constraints. Despite the fact that the corresponding optimization problem has a nonconvex fractional form, we are able to determine its locally optimal solution via Charnes-Cooper transformation and minorization-maximization algorithm. Furthermore, we study the extension to a more complicated scenario where perfect channel state information at the transmitter (CSIT) is not available. The superiority of the proposed algorithms is finally verified via simulations.