A conventional visible light communication system consists of a transmitter, a jammer that includes a few light emitting diodes, a legal listener and an eavesdropper. In this work, a similar system is designed with a collimating lens in order to create an extra layer of practical physical security measure. The use of a collimating lens makes it available to spatially limiting data transmission to an area under the lensed transmitter. Also focused data transmission through the optical lens, increases the secrecy rate. To investigate the applicability of the proposed design we designed a sample experimental setup using USRP and implemented in a laboratory environment. In the proposed set up, the receiver is in a fixed position. However, it is possible to implement an easy, practical and cheap hardware solution with respect to a beamforming type VLC that uses directional beam forming method to establish transmission to a dynamic target. In addition, it is achievable to control the size of the area where a receiver can access data by manipulating the distance between the optical lens and transmitter.
A conventional visible light communication system consists of a transmitter, a jammer that includes a few light emitting diodes, a legal listener and an eavesdropper. In this work, a similar system is designed with a collimating lens in order to create an extra layer of practical physical security measure. The use of a collimating lens makes it available to spatially limiting data transmission to an area under the lensed transmitter. Also focused data transmission through the optical lens, increases the secrecy rate. To investigate the applicability of the proposed design we designed a sample experimental setup using USRP and implemented in a laboratory environment. In the proposed set up, the receiver is in a fixed position. However, it is possible to implement an easy, practical and cheap hardware solution with respect to a beamforming type VLC that uses directional beam forming method to establish transmission to a dynamic target. In addition, it is achievable to control the size of the area where a receiver can access data by manipulating the distance between the optical lens and transmitter.
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.
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.
Visible light communication (VLC) is a new enabling communication technology that exploits illumination devices, mostly high-brightness light-emitting diodes (LEDs), to establish high-speed short-range wireless communication links. VLC is a promising technology that has gained significant interest in the last decade due to its high data rates and low cost of deployment. Although VLC systems are less susceptible to eavesdropping than RF systems since light does not penetrate through walls, they become as vulnerable as their radio-frequency (RF) counterparts when their nodes are deployed in public areas and/or when there are large windows. Thus, security for VLC systems is as important as it is for RF systems. Security in wireless communication systems may be enhanced by introducing physical layer security (PLS) techniques. In fact, PLS has been applied to a wide range of RF applications in an effort to improve the overall security by complementing existing cryptography-based security techniques. The potential of PLS stems from its ability of leveraging features of the surrounding environments via sophisticated encoding techniques at the physical layer. Indeed, PLS schemes can be applied in the same spirit to VLC systems. \n \nThere exist many specificities that characterize VLC systems, leading to major differences compared to RF systems. Specifically, VLC channels are quasi-static and real valued channels, which seemingly simplify the application of PLS techniques. However, due to the limited dynamic range of the LEDs, VLC systems impose an amplitude constraint on the channel input, which makes unbounded inputs not admissible. As a result, the performance of PLS schemes must be revised in the VLC context due to its different operating constraints. \n \nWe propose in this thesis enhancing the secrecy performance of VLC systems through PLS techniques. Firstly, we consider the degraded single-input single-output (SISO) VLC system. We derive achievable secrecy rates using continuous and discrete input distributions and we demonstrate the substantial improvement in the secrecy performance by using discrete distributions. Secondly, we consider the multiple-input single-output (MISO) VLC systems. We consider at first the case of randomly located eavesdroppers, in which we develop an associated achievable secrecy rate and we develop a beamforming-based precoding scheme that enhances the secrecy performance of this class of systems. In the second part, we consider the multi-user (MU) MISO broadcast system with confidential messages and we develop linear precoding schemes that enhance typical secrecy performance measures, including the max-min fairness and the weighted fairness. Finally, we consider the multiple-input multiple-output (MIMO) VLC system. We derive achievable secrecy rates using continuous and discrete distributions and we develop linear precoding schemes that improve its secrecy performance.
In this paper, a method is proposed for improving the physical layer security for indoor visible light communication (VLC) networks with angle diversity transmitters. An angle diversity transmitter usually consists of multiple narrow-beam light-emitting diode (LED) elements with different orientations. Angle diversity transmitters are suitable for confidential data transmission, since data transmission via narrow light beams can effectively avoid the leakage of messages. In order to improve security performance, protection zones are introduced to the systems with angle diversity transmitters. Simulation results show that over 50% performance improvement can be obtained by adding protection zones.
In order to improve the security performance of multiuser visible light communication (VLC) and facilitate the secure application of optical wireless communication technology in Internet-of-Things, we investigate the physical-layer security in a multiuser VLC system with non-orthogonal multiple access (NOMA). When the light-emitting diode (LED) transmitter communicates with multiple legitimate users by downlink NOMA, both single eavesdropper and multi-eavesdropper scenarios are considered. In the presence of single eavesdropper, based on transmission characteristics of the optical wireless channel, with known instantaneous channel state information (CSI) of the NOMA legitimate channels and statistical CSI of the eavesdropper channel, an exact expression of secrecy outage probability (SOP) is derived, which acts as a benchmark of the security performance to guide selecting or optimizing parameters of the LED transmitter and the photodiode receiver of NOMA legitimate users. In the multi-eavesdropper case, based on the spatial distribution of legitimate users and eavesdroppers, the SOP is obtained via a stochastic geometry theory, so as to guide the NOMA legitimate users to keep away from the area with high eavesdropper density. For typical parameters of the indoor LED transmitter and the PD receiver, simulation results show that the SOP performance improves with the increasing of LED transmission power or transmission signal-to-noise ratio (SNR) in both scenarios. Specifically, in the single eavesdropper case, enlarging the channel condition difference of user groups or deviating the eavesdropper from the given user group can improve the SOP performance, and for a given NOMA legitimate user, the SOP eventually settles around 0.2 while the semiangle at half illuminance of the LED varies between 15° to 60°. In the multi-eavesdropper case, we can get a better SOP performance when reducing the eavesdropper density or the semi-angle at half illuminance of the LED for a given eavesdropper density.