Enhancement of Physical Layer Security with Simultaneous Beamforming and Jamming for Visible Light Communication Systems

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

Physical Layer Security in Visible Light Communication Systems with Randomly Located Colluding Eavesdroppers

This letter investigates the secrecy performance in visible light communication (VLC) in the presence of randomly located colluding eavesdroppers (EDs). Colluding EDs can combine their observations and degrade the secrecy performance of the VLC systems. Utilizing the numerical inversion of a characteristic function, the probability distribution of the combined signal-to-noise ratio of colluding EDs is analyzed. The closed-form expression of the secrecy outage probability is derived and verified by Monte Carlo simulations

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

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

Securing Visible Light Communications with Spatial Jamming

In this paper, we propose a secure visible light communication (VLC) system with a novel spatial jamming scheme, which is inspired by practical observations of indoor VLC environments. In reality, probable and approximate locations of VLC users can be anticipated by analyzing the user behavior characteristic and the layout of the room. Based on the available location knowledge of a legitimate user (UE) and an eavesdropper (ED), an LED transmitter can choose to convey data or a jamming signal. We call this strategy spatial jamming. By employing a continuous LED model, the related optimization problems are formulated and analyzed based on the signal-to-interference-plus-noise ratio and the secrecy rate, respectively. The numerical results are provided to validate the prediction that the proposed spatial jamming scheme can effectively secure a VLC transmission even when the LEDs do not know the exact location of the ED

Highly Moldable Electrospun Clay-Like Fluffy Nanofibers for Three-Dimensional Scaffolds

The development of three-dimensional polymeric systems capable of mimicking the extracellular matrix is critical for advancing tissue engineering. To achieve these objectives, three-dimensional fibrous scaffolds with “clay”-like properties were successfully developed by coaxially electrospinning polystyrene (PS) and poly­(ε-caprolactone) (PCL) and selective leaching. As PS is known to be nonbiodegradable and vulnerable to mechanical stress, PS layers present at the outer surface were removed using a “selective leaching” process. The fibrous PCL scaffolds that remained after the leaching step exhibited highly advantageous characteristics as a tissue engineering scaffold, including moldability (i.e., clay-like), flexibility, and three-dimensional structure (i.e., cotton-like). More so, the “clay-like” PCL fibrous scaffolds could be shaped into any desired form, and the microenvironment within the clay scaffolds was highly favorable for cell expansion both in vitro and in vivo. These “electrospun-clay” scaffolds overcome the current limitations of conventional electrospun, sheet-like scaffolds, which are structurally inflexible. Therefore, this work extends the scope of electrospun fibrous scaffolds toward a variety of tissue engineering applications

Additional file 1 of Exploring the Smoking-Epilepsy Nexus: a systematic review and meta-analysis of observational studies

Additional file 1