Positive Secrecy Capacity Probability Research Articles

On security performance analysis of IRS-aided VLC/RF hybrid system

Intelligent reflecting surface (IRS) has been introduced into wireless communication to improve physical layer security (PLS) due to its ability of reconfiguring propagation environments. However, most current research on IRS-aided PLS is for standalone radio frequency (RF) or visible light communication (VLC), and few has focused on IRS-aided VLC/RF hybrid systems combining the wide coverage of RF and high speed of VLC. We study the PLS of an IRS-aided dual-hop VLC/RF hybrid system, where the first VLC link is to transmit optical signal, and the second RF link assisted by IRS is to extend communication region inaccessible to visible light, and the two hops are connected by a relay in decode-and-forward or amplify-and-forward mode. Two eavesdropping scenarios are considered: eavesdropping from IRS and eavesdropping from relay. Then, the closed-form expressions of secrecy outage probability and strictly positive secrecy capacity probability are derived for four combinations of eavesdropping scenarios and relay modes, and corresponding asymptotic solutions are obtained. Finally, simulations are carried out to verify the superiority of the proposed system over a conventional hybrid system without IRS, and the proposed system shows different security performance for various scenarios and relay modes, and IRS has a positive effect on improving PLS.

Optimal Relay Selection for Secure NOMA Systems Under Untrusted Users

The key idea of non-orthogonal multiple access (NOMA) is to serve multiple users in the same frequency band to improve the spectral efficiency. Whereas a security flaw emerges in the presence of untrusted users or low security clearance users who can access the messages of trusted users due to the spectrum sharing and may work as eavesdroppers. To achieve reliable and secure communications of NOMA systems under untrusted users, we in this paper propose two relay selection (RS) schemes termed decode-and-forward (DF) and amplify-and-forward (AF) protocols based optimal relay selection (i.e., DORS and AORS) schemes, respectively. To explicitly reveal the benefits of the DORS and AORS schemes, we derive the exact and asymptotic closed-form expressions of the secrecy outage probability (SOP) and positive secrecy capacity probability (PSCP) achieved by the two schemes, and analyze the optimality of the two schemes. Analysis and simulation results indicate that both the DORS and AORS schemes significantly outperform the benchmark schemes, in addition to achieving the same SOP and desirable PSCP at high SNR.

Evaluating Secrecy Capacity for In-Body Wireless Channels

The next generation of implanted medical devices is expected to be wireless, bringing along new security threats. Thus, it is critical to secure the communication between legitimate nodes inside the body from a possible eavesdropper. This work assesses the feasibility of securing next generation multi-nodal leadless cardiac pacemakers using physical layer security methods. The secure communication rate without leakage of information to an eavesdropper, referred to as secrecy capacity, depends on the signal-to-noise ratios (SNRs) of the eavesdropper and legitimate channels and will be used as a performance metric. Numerical electromagnetic simulations are utilized to compute the wireless channel models for the respective links. These channel models can be approximated with a log-normal distribution which can be used to evaluate the probability of positive secrecy capacity and the outage probability of this secrecy capacity. The channels are modeled for three different frequency bands and a comparison between their secrecy capacities is provided with respect to the eavesdropper distance. It has been found that the positive secrecy capacity is achievable within the personal space of the human body for all the frequency bands, with the medical implant communication systems (MICS) band outperforming others.

Physical layer security of hybrid satellite‐terrestrial relay networks with multiple colluding eavesdroppers over non‐identically distributed Nakagami‐ m fading channels

This study investigates the physical layer security of a downlink hybrid satellite-terrestrial relay network (HSTRN) where the satellite channel follows shadowed-Rician fading and terrestrial channels are assumed to undergo independent and non-identically distributed Nakagami- m fading. Herein, the authors consider a multi-antenna satellite, which communicates with a terrestrial user via an amplify-and-forward relay in the presence of multiple colluding eavesdroppers at the earth. They derive novel expressions of secrecy outage probability (SOP), ergodic secrecy capacity, and probability of positive secrecy capacity for the proposed network. They further obtain the achievable secrecy diversity order of the considered HSTRN by employing asymptotic analysis of SOP expression. Finally, numerical and simulation results are provided to validate the accuracy of the proposed analysis and to highlight the impact of a multi-antenna satellite on future wireless systems.

Analysis of the physical layer security enhancing of wireless communication system under the random mobile

User mobility is a major feature of wireless networks. At present, physical layer security research rarely considers the impact of user mobility on the physical layer security performance in the network. In this study, the authors propose a random mobile user physical layer security model and study the impact of random waypoint movement users on the security performance of the physical layer in wireless networks, in which an artificial noise security scheme under the multi-antenna transmission model is considered. They derive the closed expression of positive secrecy capacity probability and secrecy outage probability under this model. The results prove that system security is enhanced because of the users’ mobility.

Experimental Phantom-Based Security Analysis for Next-Generation Leadless Cardiac Pacemakers.

With technological advancement, implanted medical devices can treat a wide range of chronic diseases such as cardiac arrhythmia, deafness, diabetes, etc. Cardiac pacemakers are used to maintain normal heart rhythms. The next generation of these pacemakers is expected to be completely wireless, providing new security threats. Thus, it is critical to secure pacemaker transmissions between legitimate nodes from a third party or an eavesdropper. This work estimates the eavesdropping risk and explores the potential of securing transmissions between leadless capsules inside the heart and the subcutaneous implant under the skin against external eavesdroppers by using physical-layer security methods. In this work, we perform phantom experiments to replicate the dielectric properties of the human heart, blood, and fat for channel modeling between in-body-to-in-body devices and from in-body-to-off-body scenario. These scenarios reflect the channel between legitimate nodes and that between a legitimate node and an eavesdropper. In our case, a legitimate node is a leadless cardiac pacemaker implanted in the right ventricle of a human heart transmitting to a legitimate receiver, which is a subcutaneous implant beneath the collar bone under the skin. In addition, a third party outside the body is trying to eavesdrop the communication. The measurements are performed for ultrawide band (UWB) and industrial, scientific, and medical (ISM) frequency bands. By using these channel models, we analyzed the risk of using the concept of outage probability and determine the eavesdropping range in the case of using UWB and ISM frequency bands. Furthermore, the probability of positive secrecy capacity is also determined, along with outage probability of a secrecy rate, which are the fundamental parameters in depicting the physical-layer security methods. Here, we show that path loss follows a log-normal distribution. In addition, for the ISM frequency band, the probability of successful eavesdropping for a data rate of 600 kbps (Electromyogram (EMG)) is about 97.68% at an eavesdropper distance of 1.3 m and approaches 28.13% at an eavesdropper distance of 4.2 m, whereas for UWB frequency band the eavesdropping risk approaches 0.2847% at an eavesdropper distance of 0.22 m. Furthermore, the probability of positive secrecy capacity is about 44.88% at eavesdropper distance of 0.12 m and approaches approximately 97% at an eavesdropper distance of 0.4 m for ISM frequency band, whereas for UWB, the same statistics are 96.84% at 0.12 m and 100% at 0.4 m. Moreover, the outage probability of secrecy capacity is also determined by using a fixed secrecy rate.

Impact of Mobility on Physical Layer Security Over Wireless Fading Channels

Wireless physical layer security has attracted great attention in recent years. Although mobility is an intrinsic property of wireless networks, most of the existing works only consider static scenarios and the impact of mobility on wireless physical layer security is not well understood. To fill this gap, in this paper, we investigate physical layer security in the scenario with a random mobile receiver under Rayleigh fading channel. We consider a common scenario where a base station or access point communicates to a random mobile receiver with a passive eavesdropper in a circular region. The secrecy performances under three typical random mobility models are studied: random waypoint model (RWP); random direction model (RD); and border move model. We investigate the secrecy characteristics of the mobile user under steady-state running and provide a general analytical framework for computing the ergodic secrecy capacity. We derive tractable closed-form expressions of positive secrecy capacity probability and secrecy outage probability for RWP and RD mobility users, respectively. By comparing the secrecy performance of mobility with static case, we find that the RWP mobile user can achieve much better secrecy performance than the others. We then investigate the secrecy performance of RWP mobile user with pause time. Furthermore, the two types of secrecy improvement strategies for random mobile users are proposed. In the first strategy, a transmit subcell for RWP users is bounded. We allow the transmitter to communicate with the mobile user only when he is moving within the subcell. In the other strategy, the transmitter is turned on only when the evaluated secrecy performance reaches to a required level. We strike a good trade-off between the secrecy improvements and transmit outage probability. Extensive simulation results validate our theoretical analysis. Finally, we extend our framework to other realistic scenarios, including nodes moving in other shapes of areas, and multiple non-cooperative and cooperative eavesdroppers.

Secrecy performance of noncoplanar SIMOME NLOS ultraviolet communications over turbulence channels

Abstract This paper considers improving the confidentiality of non-line-of-sight (NLOS) ultraviolet (UV) links within the framework of physical-layer security. We study an NLOS UV scenario with one transmitter, one legitimate receiver and an eavesdropper. The transmitter has only one receive aperture, while the legitimate and unauthorized receivers have multiple receive apertures. Maximum ratio combining (MRC) and equal gain combining (EGC) techniques are utilized to overcome the data rate bottleneck and security risk induced by scattered UV channels and atmospheric turbulence. Alignment errors are exit in the noncoplanar single-input multiple-output multi-apertures eavesdroppers (SIMOME) NLOS UV communication system. The expressions of the average secrecy capacity (ASC), the secrecy outage probability (SOP) and the probability of positive secrecy capacity (PPSC) are derived. It is founded that the smaller the transmit or receive elevation angles are, the better the secrecy performance is. Spatial diversity techniques can improve the confidentiality of NLOS UV links with smaller off-axis errors.

SIC-Based Secrecy Performance in Uplink NOMA Multi-Eavesdropper Wiretap Channels

A new paradigm of uplink non-orthogonal multiple access along with multiple eavesdroppers to achieve secrecy transmission is studied in this paper. We investigate the secrecy performance of a single transmitter in both non-colluding- and colluding-eavesdropper scenarios on basis of two decoding methods at the legitimate receiver, zero-forcing (ZF), and minimum mean-square error (MMSE), jointly with successive interference cancellation (SIC). We first evaluate the secrecy performance in three metrics: secrecy outage probability, effective secrecy throughput (EST), and positive secrecy capacity probability. Analytical results show: 1) the collusion of eavesdroppers deteriorates the secrecy performance, which is an affine combination of those regarding each single eavesdropper and 2) MMSE-SIC outperforms ZF-SIC, while the performance gap can be overcome via reducing the number of interferers, or increasing signal-to-noise ratio (SNR), or enhancing the spatial diversity gain. We then analyze the asymptotic behaviors of the secrecy performance, revealing the high-SNR secrecy performance for both ZF-SIC and MMSE-SIC approaches to the same result which is location-dependent only. Furthermore, we study the problem of optimal power allocation to each transmitter subject to limited total transmit power. An interesting solution to this problem is demonstrated with the aid of numerical results. Finally, we propose an SIC order scheduling scheme which is conjectured to be optimal in achieving total maximum EST in a high SNR regime.

ZF-SIC Based Individual Secrecy in SIMO Multiple Access Wiretap Channel

In this paper, a decoding method of joint zero-forcing and successive interference cancellation (ZF-SIC) is put forward to assist the study of the individual secrecy in the quasi-static Rayleigh fading single-input multiple-output multiple access wiretap channel. We first evaluate the individual secrecy performance by deriving the closed-form expressions in terms of positive secrecy capacity probability, secrecy outage probability, and effective secrecy throughput (EST). Besides the expected impact of the SIC order, we find, in high signal-to-noise ratio (SNR) regime, the secrecy performance is only determined by the transmitter’s relative distance to eavesdropper over legitimate receiver rather than the SNR. Such a result prompts us to propose an SIC order scheduling scheme (alternative scheme) on basis of the transmitters’ relative distances from the shortest to the longest. It is proved optimal in achieving total maximum EST in high SNR regime. Finally, we also investigate the problem of optimal power allocation to each transmitter under the constraint of the limited total power. An interesting solution to this problem is disclosed with the aid of numerical analysis.

Accumulate and Jam: Towards Secure Communication via A Wireless-Powered Full-Duplex Jammer

This paper develops a new cooperative jamming protocol, termed accumulate-and-jam (AnJ), to improve physical layer security in wireless communications. Specifically, a full-duplex (FD) friendly jammer is deployed to secure the direct communication between source and destination in the presence of a passive eavesdropper. We consider the friendly jammer as an energy-constrained node without embedded power supply but with an energy harvesting unit and rechargeable energy storage; it can thus harvest energy from the radio frequency (RF) signals transmitted by the source, accumulate the energy in its battery, and then use this energy to perform cooperative jamming. In the proposed AnJ protocol, based on the energy status of the jammer and the channel state of source-destination link, the system operates in either dedicated energy harvesting (DEH) or opportunistic energy harvesting (OEH) mode. Thanks to the FD capability, the jammer also harvests energy from the information-bearing signal that it overhears from the source. We study the complex energy accumulation and consumption procedure at the jammer by considering a practical finite-capacity energy storage, of which the long-term stationary distribution is characterized through applying a discrete-state Markov Chain. An alternative energy storage with infinite capacity is also studied to serve as an upper bound. We further derive closed-form expressions for two secrecy metrics, i.e., secrecy outage probability and probability of positive secrecy capacity. In addition, the impact of imperfect channel state information on the performance of our proposed protocol is also investigated. Numerical results validate all theoretical analyses and reveal the merits of the proposed AnJ protocol over its half-duplex counterpart.

Performance analysis of physical layer security over α – μ fading channel

Recently, many works have focused on analyzing the metrics of physical layer security over different wireless channels, such as additive white Gaussian noise (AWGN), Rayleigh, Rician and Nakagami-m fading distributions. In order to extend the analysis to the general case, α-μ fading channel is considered, which can span the aforementioned cases. For this purpose, the physical layer security over α-μ fading channel is presented in this letter. The closed-form expressions for the probability of positive secrecy capacity and upper bound of the secrecy outage probability are derived. Their accuracies are assessed through comparison of theoretical analysis and simulations results.

Enhancing Security in Correlated Channel With Maximal Ratio Combining Diversity

In this correspondence, we consider a confidential communication through slow non-selective correlated Rayleigh fading channel, where a single antenna transmitter communicates at a pre-decided constant rate with a legitimate receiver in the presence of an eavesdropper. Both the legitimate receiver and eavesdropper are equipped with multiple antennas and employ maximal ratio combining (MRC) reception scheme. With the presence of channel diversity, we find the closed-form expressions for the probability of non-zero secrecy capacity and the outage probability of secrecy capacity in terms of channel parameters such as correlation coefficient and the ratio of main and eavesdropper channel gains that will be called average channel gain ratio (CGR). The analysis of secure outage performance with the MRC diversity scheme tells how the channel diversity enhances the secrecy capacity. We quantify the effect of antenna correlation on the probability of positive secrecy capacity and the secure outage probability. We also investigate how the target secrecy rate influences the effect of antenna correlation on the secure outage probability. Moreover, as a result of obtaining the closed-form expressions for the probability of positive secrecy capacity and the outage probability, it is insightful to see how the channel parameters affect the secure outage performance of the correlated channels.