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.
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.
This paper considers improving the confidentiality of visible light communication (VLC) links within the framework of physical-layer security. We study a VLC scenario with one transmitter, one legitimate receiver, and one eavesdropper. The transmitter has multiple light sources, while the legitimate and unauthorized receivers have a single photodetector, each. We characterize secrecy rates achievable via transmit beamforming over the multiple-input, single-output (MISO) VLC wiretap channel. For VLC systems, intensity modulation (IM) via light-emitting diodes (LEDs) is the most practical transmission scheme. Because of the limited dynamic range of typical LEDs, the modulating signal must satisfy certain amplitude constraints. Hence, we begin with deriving lower and upper bounds on the secrecy capacity of the scalar Gaussian wiretap channel subject to amplitude constraints. Then, we utilize beamforming to obtain a closed-form secrecy rate expression for the MISO wiretap channel. Finally, we propose a robust beamforming scheme to consider the scenario wherein information about the eavesdropper's channel is imperfect due to location uncertainty. A typical application of the proposed scheme is to secure the communication link when the eavesdropper is expected to exist within a specified area. The performance is measured in terms of the worst-case secrecy rate guaranteed under all admissible realizations of the eavesdropper's channel.
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.
Despite offering higher security than radio frequency (RF) channels, the broadcast nature of the visible light communication (VLC) channel makes VLC links inherently susceptible to eavesdropping by unauthorized users. In this work, we consider the physical-layer security of VLC links aided by friendly jamming. The jammer has multiple light sources, but does not have access to the data transmitted. The eavesdropper's reception is degraded by a jamming signal that causes no interference to the legitimate receiver. Due to the limited dynamic range of typical light-emitting diodes (LEDs), both the data and jamming signals are subject to amplitude constraints. Therefore, we begin with deriving a closed-form secrecy rate expression for the corresponding wiretap channel, and adopt secrecy rate as the performance measure. Then, we formulate a linear programming problem to maximize the secrecy rate when the eavesdropper's channel is accurately known to the jammer. Finally, we consider robust beamforming to maximize the worst-case secrecy rate when information about the eavesdropper's channel is uncertain due to location uncertainty. The robust scheme makes use of simple linear programming, making real-time implementation feasible in a variety of real-world scenarios.
Visible-light communication (VLC) is an enabling technology that exploits the lighting infrastructure to provide ubiquitous indoor broadband coverage via high-speed short-range wireless communication links. On the other hand, physical-layer security has the potential to supplement conventional encryption methods with an additional secrecy measure that is provably unbreakable regardless of the computational power of the eavesdropper. The lack of wave-guiding transmission media in VLC channels makes the communication link inherently susceptible to eavesdropping by unauthorized users existing in areas illuminated by the data transmitters. In this thesis, we study transmission techniques that enhance the secrecy of VLC links within the framework of physical-layer security. Due to linearity limitations of typical light-emitting diodes (LEDs), the VLC channel is more accurately modelled with amplitude constraints on the channel input, rather than the conventional average power constraint. Such amplitude constraints render the prevalent Gaussian input distribution infeasible for VLC channels, making it difficult to obtain closed-form secrecy capacity expressions. Thus, we begin with deriving lower bounds on the secrecy capacity of the Gaussian wiretap channel subject to amplitude constraints. We then consider the design of optimal beamformers for secrecy rate maximization in the multiple-input single-output (MISO) wiretap channel under amplitude constraints. We show that the design problem is nonconvex and difficult to solve, however it can be recast as a solvable quasiconvex line search problem. We also consider the design of robust beamformers for worst-case secrecy rate maximization when channel uncertainty is taken into account. Finally, we study the design of linear precoders for the two-user MISO broadcast channel with confidential messages. We consider not only amplitude constraints, but also total and per-antenna average power constraints. We formulate the design problem as a nonconvex weighted secrecy sum rate maximization problem, and provide an efficient search algorithm to obtain a solution for such a nonconvex problem. We extend our approach to handle uncertainty in channel information. The design techniques developed throughout the thesis provide valuable tools for tackling real-world problems in which channel uncertainty is almost always inevitable and amplitude constraints are often necessary to accurately model hardware limitations.
This paper considers physical layer security enhancement mechanisms that utilize simultaneous beamforming and jamming in visible light communication systems with a randomly located eavesdropper under the assumption that there are multiple light-emitting diode (LED) transmitters and one intended user. When an eavesdropper with an augmented front-end receiver is present, the jamming is very useful for preventing the eavesdropper from wiretapping the information since it is not possible to extract only the information component from the received signal if the jamming signal is random. Thus, in this paper, an optimization problem is formulated with a focus on the signal-to-interference-plus-noise ratio for the legitimate link, and it is solved by a heuristic method called the concave-convex procedure. Then, a ternary scheme is proposed, which is less complicated than the full (joint) scheme, and it is optimized by adopting a formulation based on an assignment problem, the solution of which is effectively obtained by the so-called tabu search procedure. In addition, the problem of maximizing the average secrecy rate is investigated by utilizing a continuous LED model, which significantly relaxes the complication that rises from calculating the expectation with respect to the location of the eavesdropper. Our analysis and simulation results show that the proposed simultaneous beamforming and jamming strategies (both joint and ternary) are good proxies for maximizing the average secrecy rate by utilizing the statistical information on the eavesdropper's random location.
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.