Located Eavesdroppers Research Articles

Safeguarding Millimeter Wave Communications Against Randomly Located Eavesdroppers

Millimeter wave offers a sensible solution to the capacity crunch faced by 5G wireless communications. This paper comprehensively studies physical layer security in a multi-input single-output (MISO) millimeter wave system where multiple single-antenna eavesdroppers are randomly located. Concerning the specific propagation characteristics of millimeter wave, we investigate two secure transmission schemes, namely maximum ratio transmitting (MRT) beamforming and artificial noise (AN) beamforming. Specifically, we first derive closed-form expressions of the connection probability for both schemes. We then analyze the secrecy outage probability (SOP) in both non-colluding eavesdroppers and colluding eavesdroppers scenarios. Also, we maximize the secrecy throughput under a SOP constraint, and obtain optimal transmission parameters, especially the power allocation between AN and the information signal for AN beamforming. Numerical results are provided to verify our theoretical analysis. We observe that the density of eavesdroppers, the spatially resolvable paths of the destination and eavesdroppers all contribute to the secrecy performance and the parameter design of millimeter wave systems.

Caching-Aided Physical Layer Security in Wireless Cache-Enabled Heterogeneous Networks

Caching popular contents is a promising way to offload the mobile data traffic in wireless networks, but so far the potential advantage of caching in improving physical layer security (PLS) is rarely considered. In this paper, we contribute to the design and theoretical understanding of exploiting the caching ability to improve the transmission security in a wireless heterogeneous network. Two transmission schemes, namely Symbol-level scheme and Bit-level scheme, are considered in such network to improve PLS by utilizing the content property of cached files. In Symbol-level scheme, the base station (BS) ensures the secrecy of communication by transmitting the requested file along with a pre-cached file of the user such that the eavesdropper’s channel is degraded. In Bit-level scheme, the BS encodes the requested file with a pre-cached file to fully resist the overhearing of eavesdroppers in bit level, e.g., network coding. Accordingly, the node locations of BSs, users and eavesdroppers are first modeled as mutually independent Poisson point processes and the corresponding file access protocol is developed. We consider two scenarios where each scheme is employed respectively, and then derive analytical expressions of two secrecy metrics in terms of average secrecy rate and secrecy coverage probability. Numerical results are provided to show the significant security advantages of the proposed schemes and to characterize the impacts of the cache ability and network resources on the security performance.

TPA: Prediction of Spoofing Attack Using Thermal Pattern Analysis in Ultra Dense Network for High Speed Handover Scenario

With the rising demand for a high-data rate by the subscribers, security becomes a prominent and critical issue for the emerging ultra-dense networks (UDNs). Although, more access points (APs) are involved with the purpose to strengthen the signal quality and aid in user equipment (UE) throughput enhancement. Thus, the UDN serves as a promising approach to accommodate a large number of APs (and UE’s) and ensure them with seamless connectivity and ubiquitous coverage. However, this intensification of base station (BS) densities will upsurge the handover (HO) rates for high-speed users. In this context, this paper investigates the security issues for the roaming users in UDN, pertaining to the increased HO percentage. Toward this goal, a novel approach called as thermal pattern analysis (TPA) is proposed to determine the probable region of attack, for high-speed users through tracking their footprints of thermal energy patterns (i.e., energy and spectral efficiency). We also perform the secrecy capacity check on wandering users, considering the fact that eavesdropper (or Eve) location is erratic. Comprehensive simulations are performed for real-time deployment and results validate the effectiveness of the proposed approach. Consequently, thermal analysis can be performed for all variety of mobile communication scenarios to uncover the adversary tremor. A real-time implementation using hardware components related to the prototype study has been carried out to access the performance in the actual world. From the analysis of the results, it is quite evident that TPA is more accurate in finding the probable region of low security for the UDN environment.

Probabilistic Caching Placement in the Presence of Multiple Eavesdroppers

The wireless caching has attracted a lot of attention in recent years, since it can reduce the backhaul cost significantly and improve the user‐perceived experience. The existing works on the wireless caching and transmission mainly focus on the communication scenarios without eavesdroppers. When the eavesdroppers appear, it is of vital importance to investigate the physical‐layer security for the wireless caching aided networks. In this paper, a caching network is studied in the presence of multiple eavesdroppers, which can overhear the secure information transmission. We model the locations of eavesdroppers by a homogeneous Poisson Point Process (PPP), and the eavesdroppers jointly receive and decode contents through the maximum ratio combining (MRC) reception which yields the worst case of wiretap. Moreover, the main performance metric is measured by the average probability of successful transmission, which is the probability of finding and successfully transmitting all the requested files within a radius R. We study the system secure transmission performance by deriving a single integral result, which is significantly affected by the probability of caching each file. Therefore, we extend to build the optimization problem of the probability of caching each file, in order to optimize the system secure transmission performance. This optimization problem is nonconvex, and we turn to use the genetic algorithm (GA) to solve the problem. Finally, simulation and numerical results are provided to validate the proposed studies.

On the security of K-tier heterogeneous cellular networks

Motivated by recent developments in heterogeneous cellular networks and physical-layer security, we aim to characterize the fundamental limits of secure communication in networks. Based on a general model in which both transmitters and receivers are randomly scattered in space, we model the locations of K-tier base stations, users, and potential eavesdroppers as independent two-dimensional Poisson point processes. Using the proposed model, we analyze the achievable secrecy rates for an arbitrarily located mobile user. Assuming that the cell selection is based on achievable-secrecy-rate threshold, we obtain approximations for: (a) secrecy coverage probability and (b) average secrecy load per tier. We also investigate how the network performance is affected by secrecy rate threshold, eavesdropper density, and different access strategies are analyzed, respectively. Finally, our theoretical claims are confirmed by the numerical results.

Exploiting Opportunistic Scheduling in Uplink Wiretap Networks

Opportunistic scheduling schemes are investigated for uplink wiretap channels with multiple asymmetrically located legitimate users (LUs) and eavesdroppers. To exploit multiuser diversity, the cumulative distribution function-based scheduling method is leveraged to schedule the transmissions of the LUs. Under this scheduling framework, the closed-form expressions of the secrecy outage probability and ergodic secrecy rate are derived, illustrating the interplay among the system parameters, such as the channel statistics and the number of LUs and eavesdroppers. Through the secrecy outage analysis of the proposed scheduling schemes, we observe that the secrecy throughput is not always maximized with a larger channel access ratio (CAR), and consequently, we design a CAR adjustment scheme to maximize the secrecy throughput while satisfying the required secrecy level. We also prove that under our proposed scheduling schemes, the secrecy diversity order of each LU is equal to the reciprocal of the LU's CAR, implying that full diversity order is achieved, and the ergodic secrecy rate of each LU normalized by its CAR achieves the optimal double-logarithmic growth when the number of LUs increases to infinity.

Energy-Efficient Secrecy in Wireless Networks Based on Random Jamming

This paper considers secure energy-efficient routing in the presence of multiple passive eavesdroppers. Previous work in this area has considered secure routing assuming probabilistic or exact knowledge of the location and channel-state-information (CSI) of each eavesdropper. In wireless networks, however, the locations and CSIs of passive eavesdroppers are not known, making it challenging to guarantee secrecy for any routing algorithm. We develop an efficient (in terms of energy consumption and computational complexity) routing algorithm that does not rely on any information about the locations and CSIs of the eavesdroppers. Our algorithm guarantees secrecy even in disadvantaged wireless environments, where multiple eavesdroppers try to eavesdrop each message, are equipped with directional antennas, or can get arbitrarily close to the transmitter. The key is to employ additive random jamming to exploit inherent non-idealities of the eavesdropper's receiver, which makes the eavesdroppers incapable of recording the messages. We have simulated our proposed algorithm and compared it with existing secrecy routing algorithms in both single-hop and multi-hop networks. Our results indicate that when the uncertainty in the locations of eavesdroppers is high and/or in disadvantaged wireless environments, our algorithm outperforms existing algorithms in terms of energy consumption and secrecy.

Safeguarding Decentralized Wireless Networks Using Full-Duplex Jamming Receivers

In this paper, we study the benefits of full-duplex (FD) receiver jamming in enhancing the physical-layer security of a two-tier decentralized wireless network with each tier deployed with a large number of pairs of a single-antenna transmitter and a multi-antenna receiver. In the underlying tier, the transmitter sends unclassified information, and the receiver works in the halfduplex (HD) mode receiving the desired signal. In the overlaid tier, the transmitter deliveries confidential information in the presence of randomly located eavesdroppers, and the receiver works in the FD mode radiating jamming signals to confuse eavesdroppers and receiving the desired signal simultaneously. We provide a comprehensive performance analysis and network design under a stochastic geometry framework. Specifically, we consider the scenarios where each FD receiver uses single- and multi-antenna jamming, and analyze the connection probability and the secrecy outage probability of a typical FD receiver by providing accurate expressions and more tractable approximations for the two metrics. We further determine the optimal deployment of the FD-mode tier in order to maximize networkwide secrecy throughput subject to constraints including the given dual probabilities and the network-wide throughput of the HD-mode tier. Numerical results are demonstrated to verify our theoretical findings, and show that network-wide secrecy throughput is significantly improved by properly deploying the FD-mode tier.

Optimal and Robust Beamforming for Secure Transmission in MISO Visible-Light Communication Links

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.

Location-Based Beamforming and Physical Layer Security in Rician Wiretap Channels

We propose a new location-based beamforming (LBB) scheme for wiretap channels, where a multi-antenna source communicates with a single-antenna legitimate receiver in the presence of a multi-antenna eavesdropper. We assume that all channels are in a Rician fading environment, the channel state information from the legitimate receiver is perfectly known at the source, and that the only information on the eavesdropper available at the source is her location. We first describe how the optimal beamforming vector that minimizes the secrecy outage probability of the system is obtained, illustrating its dependence on the eavesdropper's location. We then derive an easy-to-compute expression for the secrecy outage probability when our proposed LBB scheme is adopted. We also consider the positive impact a friendly jammer can have on our beamforming solution, showing how the path to optimality remains the same. Finally, we investigate the impact of location uncertainty on the secrecy outage probability, showing how our solution can still allow for secrecy even when the source only has a noisy estimate of the eavesdropper's location. Our work demonstrates how a multi-antenna array, operating in the most general channel conditions and most likely system set-up, can be configured rapidly in the field so as to deliver an optimal physical layer security solution.

Performance study of hybrid decode–amplify–forward (HDAF) relaying scheme for physical layer security in wireless cooperative network

SummaryIn this paper, the secrecy performance and power allocation of the signal‐to‐noise ratio‐based hybrid decode–amplify–forward (HDAF) relaying protocol in wireless cooperative network are investigated to get security at physical layer. The performance metrics considered are secrecy rate and intercept probability. The Ergodic secrecy rate is approximated theoretically. The effect of relay and eavesdropper locations on the secrecy performance of the system is analyzed. It is found that maximum secrecy rate is obtained for the relay close‐to‐destination case and minimum for the relay close‐to‐eavesdropper case. Jamming schemes are superior in secrecy rate performance than without jamming schemes. To enhance the secrecy rate further with the optimized relay and jammer powers, invasive weed optimization (IWO) algorithm‐based power allocation is proposed. Here, maximizing the secrecy rate is defined as the cost function for the proposed IWO algorithm‐based power allocation. Comparative study is done over the conventional equal and proposed power allocation schemes for validation. The proposed power allocation scheme proved to be superior. Copyright © 2016 John Wiley & Sons, Ltd.

A Half-Duplex Self-Protection Jamming Approach for Improving Secrecy of Block Transmissions in Underwater Acoustic Channels

Block transmissions are commonly used in underwater acoustic communications due to the large delay spread of the underlying channels. In this paper, we propose a novel jamming protocol based on the half-duplex nature of the underwater transceivers and the block-based transmission structure, taking advantage of the large propagation delays of underwater acoustic channels to create interference at the eavesdropper without affecting the reception of the intended user. This half-duplex jamming protocol acts like a self-protection scheme, which does not need any helpers but instead relies on the legitimate receiver itself to transmit jamming signals for the improvement of secrecy rate. The simulation results evaluate the secrecy rate improvement as a function of the eavesdropper locations.

Jamming-Aided Secure Communication in Massive MIMO Rician Channels

In this paper, we investigate the artificial noise-aided jamming design for a transmitter equipped with large antenna array in Rician fading channels. We figure out that when the number of transmit antennas tends to infinity, whether the secrecy outage happens in a Rician channel depends on the geometric locations of eavesdroppers. In this light, we first define and analytically describe the secrecy outage region (SOR), indicating all possible locations of an eavesdropper that can cause secrecy outage. After that, the secrecy outage probability (SOP) is derived, and a jamming-beneficial range, i.e., the distance range of eavesdroppers which enables uniform jamming to reduce the SOP, is determined. Then, the optimal power allocation between messages and artificial noise is investigated for different scenarios. Furthermore, to use the jamming power more efficiently and further reduce the SOP, we propose directional jamming that generates jamming signals at selected beams (mapped to physical angles) only, and power allocation algorithms are proposed for the cases with and without the information of the suspicious area, i.e., possible locations of eavesdroppers. We further extend the discussions to multiuser and multi-cell scenarios. At last, numerical results validate our conclusions and show the effectiveness of our proposed jamming power allocation schemes.

Multi-Antenna Transmission With Artificial Noise Against Randomly Distributed Eavesdroppers

In this paper, we study the secure multi-antenna transmission with artificial noise (AN) under slow fading channels coexisting with randomly located eavesdroppers. We provide a comprehensive secrecy performance analysis and system design/optimization under a stochastic geometry framework. Specifically, we first evaluate the secrecy outage performance, and derive a closed-form expression for the optimal power allocation ratio of the information signal power to the total transmit power that minimizes the secrecy outage probability (SOP). Subject to a SOP constraint, we then propose a dynamic parameter transmission scheme (DPTS) and a static parameter transmission scheme (SPTS) to maximize secrecy throughput, and provide explicit solutions on the optimal transmission parameters, including the wiretap code rates, the on-off transmission threshold and the power allocation ratio. Our results give new insight into secure transmission designs. For example, secrecy rate is a concave function of the power allocation ratio in DPTS, and AN plays a significant role under SOP constraints and in dense eavesdropper scenarios. In SPTS, transmission probability is a concave function of the power allocation ratio, and secrecy throughput is a quasi-concave function of the secrecy rate. Numerical results are demonstrated to validate our theoretical analysis.

The Thinnest Path Problem

We formulate and study the thinnest path problem for secure communication in wireless ad hoc networks. The objective is to find a path from a source to its destination that results in the minimum number of nodes overhearing the message by a judicious choice of relaying nodes and their corresponding transmission powers. We adopt a directed hypergraph model of the problem and establish the NP-completeness of the problem in 2-D networks. We then develop two polynomial-time approximation algorithms that offer √(n/2) and n/2√(n-1) approximation ratios for general directed hypergraphs (which can model nonisotropic signal propagation in space) and constant approximation ratios for ring hypergraphs (which result from isotropic signal propagation). We also consider the thinnest path problem in 1-D networks and 1-D networks embedded in a 2-D field of eavesdroppers with arbitrary unknown locations (the so-called 1.5-D networks). We propose a linear-complexity algorithm based on nested backward induction that obtains the optimal solution for both 1-D and 1.5-D networks. This algorithm does not require the knowledge of eavesdropper locations and achieves the best performance offered by any algorithm that assumes complete location information of the eavesdroppers.

Location-Based Secure Transmission for Wiretap Channels

Location information has been shown to be useful for a wide variety of applications in wireless networks, while its role in physical layer security has so far drawn little attention. In this work, we propose a new location-based secure transmission scheme for wiretap channels, where the accurate locations of the sources, destinations and any other authorized transceivers are known, but only an estimate of the eavesdropper's location is available. We outline how such an estimate of the eavesdropper's location can still allow for quantitative assessment of key security metrics. To provide focus, we describe how optimization of the effective secrecy throughput of a relay wiretap channel is obtained in our scheme, and investigate in detail the impact of the location uncertainty on the system performance. The work reported here provides insights into the design of new location-based physical layer security schemes in which the only information available on an eavesdropper is a noisy estimate of her location.

On Transmission Secrecy Outage of a Multi-Antenna System With Randomly Located Eavesdroppers

This letter studies the physical-layer security of a multi-antenna transmission system in the presence of Poisson distributed eavesdroppers. The transmission secrecy outage probability (TSOP) is adopted to evaluate the security. We derive an accurate integral expression as well as a closed-form upper bound on TSOP for the noncolluding eavesdroppers' case and a closed-form solution for the colluding eavesdroppers' case, respectively. Based on these, we define a novel concept of security region to intuitively illustrate the security from a spatial perspective. We further analyze the impacts of various factors on the security, such as the number of transmit antennas, the node intensity, and the target secrecy rate.

Secrecy Rates in Broadcast Channels with Confidential Messages and External Eavesdroppers

In this paper, we consider the broadcast channel with confidential messages and external eavesdroppers (BCCE), where a multi-antenna base station simultaneously communicates to multiple potentially malicious users, in the presence of randomly located external eavesdroppers. Using the proposed model, we study the secrecy rates achievable with regularized channel inversion (RCI) precoding by performing a large-system analysis that combines results from stochastic geometry and random matrix theory, where the number of users K and the number of transmit antennas N both grow to infinity in a fixed ratio. We obtain explicit expressions for the probability of secrecy outage and an upper bound on the rate loss due to the presence of external eavesdroppers. We show that both these quantities scale as \fraclambda_esqrt{N} as the density of external eavesdroppers λ_e grows, irrespective of their collusion strategy. Furthermore, we derive a practical rule for the choice of the regularization parameter, which is agnostic of channel state information and location of eavesdroppers, and yet provides close to optimal performance.

Unicasting on the Secrecy Graph

We consider the secrecy capacity of unicast channels of ad hoc networks exposed to randomly located eavesdroppers, as modeled by S-Graphs. Expressions that quantify the impact of fading and of the density of legitimate nodes relative to that of eavesdroppers are obtained, in terms of the probability that secrecy capacities of unicast channels are nonzero. The results indicate that depending on the relative density of eavesdroppers and the fading intensity, the secrecy capacity of unicast channels subject to fading may be higher than under additive white Gaussian noise (AWGN).

The Effect of Eavesdroppers on Network Connectivity: A Secrecy Graph Approach

This paper investigates the effect of eavesdroppers on network connectivity, using a wiretap model and percolation theory. The wiretap model captures the effect of eavesdroppers on link security. A link exists between two nodes only if the secrecy capacity of that link is positive. Network connectivity is defined in a percolation sense, i.e., connectivity exists if an infinite connected component exists in the corresponding secrecy graph. We consider uncertainty in location of eavesdroppers, which is modeled directly at the network level as correlated failures in the secrecy graph. Our approach attempts to bridge the gap between physical layer security under uncertain channel state information and network level connectivity under secrecy constraints. For square and triangular lattice secrecy graphs, we obtain bounds on the percolation threshold, which is the critical value of the probability of occurrence of an eavesdropper, above which network connectivity does not exist. For Poisson secrecy graphs, degree distribution and mean value of upper and lower bounds on node degree are obtained. Further, inner and outer bounds on the achievable region for network connectivity are obtained. Both analytic and simulation results show that uncertainty in location of eavesdroppers has a dramatic effect on network connectivity in a secrecy graph.