Providing security guarantees for the information “traveling” through the air is of critical importance for today's applications. Previous research concentrated on studying this problem when the medium used for communication is radio frequency (RF) channels. However, providing security guarantees on RF channels is a complicated task as RF channels' conditions are prone to rapid variations due small scale fading and at a given moment it is difficult to predict which of the main or wiretapper's channel has a better quality. Wireless optical communication is inherently more secure than regular RF communication. Despite this fact, optical communication is not completely immune against wiretapping and signal interception. The purpose of this paper is to study the secrecy capacity of a direct detection optical communication system. For the degraded Poisson wiretap channel, we give a complete characterization of the secrecy capacity in terms of the system parameters.
Providing security guarantees for the information “traveling” through the air is of critical importance for today's applications. Previous research concentrated on studying this problem when the medium used for communication is radio frequency (RF) channels. However, providing security guarantees on RF channels is a complicated task as RF channels' conditions are prone to rapid variations due small scale fading and at a given moment it is difficult to predict which of the main or wiretapper's channel has a better quality. Wireless optical communication is inherently more secure than regular RF communication. Despite this fact, optical communication is not completely immune against wiretapping and signal interception. The purpose of this paper is to study the secrecy capacity of a direct detection optical communication system. For the degraded Poisson wiretap channel, we give a complete characterization of the secrecy capacity in terms of the system parameters.
Providing security guarantees for wireless communication is critically important for today's applications. While previous work in this area has concentrated on radio frequency (RF) channels, providing security guarantees for RF channels is inherently difficult because they are prone to rapid variations due small scale fading. Wireless optical communication, on the other hand, is inherently more secure than RF communication due to the intrinsic aspects of the signal propagation in the optical and near-optical frequency range. In this paper, secure communication over wireless optical links is examined by studying the secrecy capacity of a direct detection system. For the degraded Poisson wiretap channel, a closed-form expression of the secrecy capacity is given. A complete characterization of the general rate-equivocation region is also presented. For achievability, an optimal code is explicitly constructed by using the structured code designed by Wyner for the Poisson channel. The converse is proved in two different ways: the first method relies only on simple properties of the conditional expectation and basic information theoretical inequalities, whereas the second method hinges on the recent link established between minimum mean square estimation and mutual information in Poisson channels.
Optical and near-optical band communication systems are known to be intrinsically more secure than comparable RF channels, due to their narrow beamwidths and, in some cases, their high atmospheric absorption. The use of coding against wiretapping for such channels is investigated. For the degraded Poisson wiretap channel model, the secrecy capacity is determined exactly. Moreover, a complete characterization of the rate-equivocation region is presented. For achievability, an optimal code is constructed explicitly by using a code designed by Wyner for the Poisson channel. The converse is proved in two ways: the first method leverages the low-SNR nature of the channel and relies only on simple properties of conditional expectation and classical information inequalities. The second method uses a link recently established between minimum mean square error estimation and mutual information over Poisson channels.
This paper addresses the degraded discrete-time Poisson wiretap channel (DT--PWC) in an optical wireless communication system based on intensity modulation and direct detection. Subject to nonnegativity, peak- and average-intensity as well as bandwidth constraints, we study the secrecy-capacity-achieving input distribution of this wiretap channel and prove it to be unique and discrete with a finite number of mass points; one of them located at the origin. Furthermore, we establish that every point on the boundary of the rate-equivocation region of this wiretap channel is also obtained by a unique and discrete input distribution with finitely many mass points. In general, the number of mass points of the optimal distributions is greater than two. This is in contrast with the degraded continuous-time PWC when the signaling bandwidth is not restricted and where the secrecy capacity and the entire boundary of the rate-equivocation region are achieved by binary distributions. Furthermore, we extend our analysis to the case where only an average-intensity constraint is active. For this case, we find that the secrecy capacity and the entire boundary of the rate-equivocation region are attained by discrete distributions with countably \textit{infinite} number of mass points, but with finitely many mass points in any bounded interval.
This paper addresses the degraded discrete-time Poisson wiretap channel (DT-PWC) in an optical wireless communication system based on intensity modulation and direct detection (IM-DD). Subject to nonnegativity, average-intensity, and bandwidth constraints, we find that the secrecy capacity and the entire boundary of the rate-equivocation region are attained by discrete distributions with a countably infinite number of mass points, but with finitely many mass points in any bounded interval. Additionally, we shed light on the asymptotic behavior of the secrecy capacity in the regimes where the average intensity constraint either tends to zero (low-intensity) or tends to infinity (high-intensity). In the low-intensity regime, we observe that: when the channel gains of the legitimate receiver and the eavesdropper are identical, the secrecy capacity scales linearly in the average-intensity ε; whereas when the channel gains are different, the secrecy capacity scales, to within a constant, like(αB−αE)EloglogE1, where αBand αEare the legitimate receiver's and the eavesdropper's channel gains, respectively. In the high-intensity regime, we establish that the secrecy capacity does not scale with the average intensity constraint.
The emergence of an array of new wireless networks has led researchers to evaluate the prospect of utilizing the physical properties of the wireless medium in order to design secure systems. In this paper, the physical layer secrecy performance of a mixed radio frequency-free space optical (RF-FSO) system with variable gain relaying scheme is investigated in the presence of an eavesdropper. We assume that the eavesdropper can wiretap the transmitted confidential data from the RF link only. It is further assumed that the main and eavesdropper RF links are modeled as generalized Gamma (GG) fading channel, and the free space optical (FSO) link experiences Málaga turbulence with pointing error impairment. Our primary concern is to protect this confidential information from being wiretapped. Besides pointing error, the atmospheric turbulence and two types of detection techniques (i.e. heterodyne detection and intensity modulation with direct detection) are also taken into consideration. Utilizing amplify-and-forward (AF) scheme, the novel mathematical closed-form expressions for average secrecy capacity, lower bound of secrecy outage probability, and strictly positive secrecy capacity are derived. As both the links (RF and FSO) undergo generalized fading channels, the derived expressions are also general. We present a unification of some existing works utilizing the proposed model to better clarify the novelty of this work. Finally, all the derived expressions are justified via Monte-Carlo simulations.
In physical-layer security, communication secrecy is commonly achieved by providing the legitimate receiver a physical-layer advantage over the eavesdropper or, equivalently, by making the eavesdropper's channel more degraded than the legitimate receiver's, a setting traditionally known as the degraded wiretap channel. There may be situations, however, where such advantages cannot be guaranteed. One example is the wireless channel where the legitimate receiver's channel may be more degraded than the eavesdropper's owing to a deep fade (outage), additive interference at the edge of a network cell, etc. To our knowledge, such scenarios have not been remedied in the related literature. Thus, we propose in this work the first physical-layer security scheme that achieves communication in a setting where the eavesdropper has the physical-layer advantage over the legitimate receiver, a scenario that we call the reversely-degraded wiretap channel. Precisely, we show that by constraining the transmitter's input to be discrete uniformly distributed (such as an on-off keying modulation) and by using nonlinear threshold-based signal detection, the legitimate receiver is guaranteed to have a positive secrecy capacity even though the eavesdropper has a better signal-to-noise ratio (SNR). The former requirement on the input distribution is to limit the capacity gains of the eavesdropper at high SNR. The latter requirement allows the communication channel to exhibit supra-threshold stochastic resonance, a phenomenon whereby noise improves signal detection and increases the mutual information. A numerical example is provided to confirm our claims.