Main-to-eavesdropper Ratio Research Articles

Physical Layer Security of Cognitive Ambient Backscatter Communications for Green Internet-of-Things

The future sixth generation (6G) wireless communication networks will face the challenges of large-scale connections green communication. To meet these requirements, cognitive ambient backscatter communication (C-AmBC) has been proposed as a new spectrum paradigm for the green Internet-of-Things (IoT) with stringent energy and spectrum constraints, in which the backscatter device (BD) can achieve communications by simultaneously sharing both spectrum and radio-frequency (RF) sources. However, due to the broadcasting nature of wireless communication channels, BD is vulnerable to eavesdropping from unlicensed eavesdroppers. To address this, this paper proposes a framework of C-AmBC networks in the presence of an unlicensed eavesdropper. Specifically, we investigate the reliability and security of the proposed framework by invoking the outage probability (OP) and intercept probability (IP) with analytical derivations. In addition, the asymptotic behaviors are conducted for the OP in the high signal-to-noise ratio (SNR) regime and IP in the high main-to-eavesdropper ratio (MER) regime. Extensive analytical and computer simulated performance evaluation results show that: 1) when the considered system is under high SNR, the OP of the legitimate user and BD tends to be a non-zero fixed constant, indicating that the existence of error floors for the diversity orders; 2) the performance trade-off of reliability and security can be optimized by adjusting various parameters of the considered system; 3) with the increase of MER, the security of the legitimate user increases, while that of BD decreases.

Modified Backscatter Communication Model for Wireless Communication Network Applications

The green communication and large-scale connection issues will be faced by the wireless communication networks with futuristic sixth generation (6G) technology. The radio-frequency (RF) and spectrum sources may be shared simultaneously to achieve optimal communication in these networks by means of backscatter devices (BD) that may function in constrained spectrums as well as the stringent energy scenarios of green Internet-of-things (IoT) by means of the proposed novel modified backscatter communication model (BCM). Unlicensed eavesdroppers may interfere with the BD due to its vulnerability caused by the wireless communication channels and their broadcasting nature. The intrusion of an unlicensed eavesdropper is detected in an efficient manner by means of the proposed BCM. The analytical derivations of intercept probability (IP) and outage probability (OP) are invoked to analyze the security and reliability of the proposed architecture. Under high main-to-eavesdropper ratio (MER) regime, the IP and under high signal-to-noise ratio (SNR) regime, the OP asymptotic behaviors are estimated additionally. Based on the results of performance evaluation, it is evident that there is a decrease in the security of BD with the increase in MER while there is a simultaneous increase in the legitimate user security. Various system parameters may be adjusted for optimizing the security and reliability performance trade-off. For diverse orders, the existence of error floors are indicated by the non-zero fixed constant of BD and the legitimate user’s OP when high SNR value is observed at the system.

Hardware Impaired Ambient Backscatter NOMA Systems: Reliability and Security

Non-orthogonal multiple access (NOMA) and ambient backscatter communication have been envisioned as two promising technologies for the Internet-of-things due to their high spectral efficiency and energy efficiency. Motivated by this fact, we consider an ambient backscatter NOMA system in the presence of a malicious eavesdropper. Under the realistic assumptions of residual hardware impairments (RHIs), channel estimation errors (CEEs) and imperfect successive interference cancellation (ipSIC), we investigate the physical layer security (PLS) of the ambient backscatter NOMA systems with emphasis on reliability and security. In order to further improve the security of the considered system, an artificial noise scheme is proposed where the radio frequency (RF) source acts as a jammer that transmits interference signals to the legitimate receivers and eavesdropper. On this basis, the analytical expressions for the outage probability (OP) and the intercept probability (IP) are derived. To gain more insights, the asymptotic analysis and corresponding diversity orders for the OP in the high signal-to-noise ratio (SNR) regime are carried out, and the asymptotic behaviors of the IP in the high main-to-eavesdropper ratio (MER) region are explored as well. Finally, the correctness of the theoretical analysis is verified by the Monte Carlo simulation results. These results show that compared with the non-ideal conditions, the reliability of the considered system is high under ideal conditions, but the security is low.

Cognitive AmBC-NOMA IoV-MTS Networks With IQI: Reliability and Security Analysis

Internet-of-Vehicle (IoV) enabled Maritime Transportation Systems (MTS) communication is anticipated to support ultra-reliable and low latency, diverse quality-of-service (QoS) and large-scale connectivities. To meet such stringent demands, a cognitive ambient backscatter non-orthogonal multiple access (C-AmBC-NOMA) IoV-MTS network is proposed. We explore the reliable and secure performance of the proposed C-AmBC-NOMA IoV-MTS network with in-phase and quadrature phase imbalance (IQI) at radio-frequency (RF) front-ends and the existence of an eavesdropper. In particular, the analytical expressions on the outage probability (OP) and intercept probability (IP) are obtained after a series of calculations. For a deeper understanding, we discuss the asymptotic behavior of OPs in the high signal-to-noise ratio (SNR) region, the diversity orders of OPs, and IPs in the high main-to-eavesdropper ratio (MER) regime. The results of Monte-Carlo simulation and a series of corresponding theoretical analysis show that: i) As the SNR approaches infinity, the OPs tend to be fixed non-negative values, indicating that the diversity orders of the OPs have error floors; ii) When the MER approaches infinity, the IPs of legitimate users decrease continuously, while the IP of backscatter device (BD) increases; iii) Compared with the system performance under ideal condition, the system performance is less reliable under IQI condition, but the security performance is enhanced; iv) By carefully selecting the system parameters, a trade-off can be achieved between reliability and security.

Secrecy Outage and Diversity Analysis of Multiple Cooperating Source-Destination Pairs

We study the physical-layer security of multiple source-destination (SD) pairs communicating within a wireless network in the face of an eavesdropper attacking the SD pairs. In order to protect the wireless transmission against eavesdropping, we propose a cooperation framework relying on two stages. Specifically, an SD pair is selected to access the total allocated spectrum using an appropriately designed scheme at the beginning of the first stage. The other source nodes (SNs) simultaneously transmit their data to the SN of the above-mentioned SD pair relying on orthogonal resources during the first stage. Then, the SN of the chosen SD pair transmits the data packets containing its own messages and the other SNs’ messages to its dedicated destination node (DN) in the second stage. Finally, this dedicated DN will forward all the other DNs’ data to the application center via the core network. We conceive a specific SD pair selection scheme, termed as the transmit antenna selection aided source-destination pair selection (TAS-SDPS). We continue by deriving the secrecy outage probability (SOP) expressions of both the TAS-SDPS conceived, as well as of the conventional round-robin source-destination pair selection (RSDPS) and of the conventional non-cooperative (Non-coop) schemes for comparison. Furthermore, we carry out the secrecy diversity gain analysis in the high main-to-eavesdropper ratio (MER) region, showing that the TAS-SDPS scheme is capable of achieving the maximum attainable secrecy diversity order. Additionally, we show that increasing the number of transmitting pairs will reduce the SOP, whilst increasing the secrecy diversity order of the TAS-SDPS scheme. It is demonstrated that the SOP of the TAS-SDPS scheme is better than that of the RSDPS and of the conventional Non-coop schemes. We also demonstrate that the secrecy diversity gain of the proposed TAS-SDPS scheme is $M$ times that of the RSDPS scheme in the high-MER region, where $M$ is the number of the SD pairs.

Secure Cache-Aided Multi-Relay Networks in the Presence of Multiple Eavesdroppers

In this paper, we investigate the security of a cache-aided multi-relay communication network in the presence of multiple eavesdroppers, where each relay can pre-store a part of the requested files in order to assist secure data transmission from source to destination. If the relays have cached the requested file, then they can directly send it to the destination; otherwise, traditional dual-hop data transmission is used. For both cases, relay selection is performed to assist the secure data transmission. We analyze the network secrecy performance in both scenarios of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">non-colluding</i> and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">colluding</i> eavesdroppers, and obtain a closed-form expression for the average secrecy outage probability (SOP), as well as an asymptotic expression for the high main-to-eavesdropper ratio (MER). Through minimizing the network SOP, we further optimize the cache placement by proposing a stochastic sampling based cache learning (SacLe) strategy, which can be implemented in parallel and thus reduces the implementation latency substantially. Numerical and simulation results are finally presented to verify the proposed analysis, and show that the caching strategy has a significant impact on the network secrecy performance through affecting the caching diversity gain and signal cooperation gain at the relays. The proposed SacLe strategy is shown to be able to achieve the optimal performance obtained by the brute force (BF) algorithm.

The Security of Cognitive Multiuser Networks Over Space-and-Time Correlated Channels

In this paper, we investigate the secrecy performance of cognitive multi-input multi-output multiuser (MIMO-MU) wiretap networks over space-and-time correlated fading channels. Specifically, we propose a joint transmit antenna selection (TAS) and multiuser scheduling scheme to improve the security of the considered system. To thoroughly analyze the impact of the joint TAS and multiuser scheduling scheme and the channel correlation on the physical layer security, the new exact and asymptotic closed-form expressions for the secrecy outage probability of cognitive MIMO-MU wiretap networks are derived in two distinct scenarios, i.e., space-and-time correlated fading channels and independent-and-perfect fading channels. From the theoretical and simulation results, several important remarks are concluded as follows. 1) The channel space correlation does not affect the achievable secrecy diversity order in a high main-to-eavesdropper ratio (MER) regime. While it produces different impacts on the secrecy performance with different values of the MER in a low MER regime. 2) The channel time correlation on the main channel can reduce the achievable secrecy diversity order from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$N_{\rm A}N_{\rm B}$</tex-math></inline-formula> to 1. 3) The joint TAS and multiuser scheduling scheme can achieve better performance than the traditional random scheduling scheme over space-and-time correlated fading channels.

The Security–Reliability Tradeoff of Multiuser Scheduling-Aided Energy Harvesting Cognitive Radio Networks

We study the physical-layer security of a cognitive radio system in the face of multiple eavesdroppers (EDs), which is composed of a secondary base station (SBS), multiple secondary users (SUs) as well as a pair of primary transmitter (PT) and primary receiver (PR), where the SUs first harvest energy from their received radio frequency signals transmitted by the PT and then communicate with the SBS relying on opportunistic scheduling. We consider two specific user scheduling schemes, namely, the channel-aware user scheduling (CaUS) and the energy-aware user scheduling (EaUS). In the CaUS scheme, an SU having the best instantaneous SU-SBS link (spanning from SUs to SBS) will be activated to communicate with the SBS. By contrast, the EaUS scheme takes into account both the amount of energy harvested from the PT and the instantaneous quality of the SU-SBS link. We analyze the security–reliability tradeoff (SRT) of both the CaUS and EaUS schemes in terms of their intercept versus outage probability. We also provide the SRT analysis of traditional round-robin user scheduling (RrUS) used as a benchmarker of the CaUS and EaUS schemes. We demonstrate that the EaUS scheme achieves the best outage and secrecy performance in the high main-to-eavesdropper ratio (MER) region, but a worse secrecy performance than the CaUS method in the low-MER region. Moreover, from a security versus reliability perspective, the CaUS outperforms both the EaUS and the RrUS in the low-MER region. Surprisingly, this also implies that although the user scheduling criterion of EaUS exploits the knowledge of both the amount of harvested power and instantaneous channel state information (CSI), it exhibits a degraded physical-layer security in the low-MER region due to the fact that the increased harvested energy is beneficial not only for the legitimate SBS receiver but also for the EDs.

Secure cache-aided multiuser UAV-relay networks with outdated channel state information

In this paper, we investigate a secure communication of UAV-relaying systems, where multiple users attempt to deliver confidential messages to the destination with the aid of a relay, yet the confidential messages can be overheard by the eavesdropper. To enhance the physical-layer security of the considered system, we propose to equip the relay with cache, and accordingly, two user selection criteria are proposed with the purposes of maximizing the channel gain of direct main link and minimizing the channel gain of direct eavesdropper link, respectively. Moreover, we take into account the effects of outdated channel state information (CSI) on the user selection criteria, and derive the secrecy outage probabilities (SOPs) for the conventional and cache-aided systems regarding both user selection criteria. In further, the asymptotic SOPs in the high signal-to-noise ratio (SNR) and main-to-eavesdropper ratio (MER) region are provided as well to illustrate the difference between the secure performances of systems with and without cache. From the given SOPs, we find that cache-aided system can achieve better secure performance in comparison with the system without cache. In addition, the multiuser diversity gain is weakened by the outdated CSI, and therefore, the diversity order of system cannot exceed two regardless of the employment of cache.

Performance evaluation of amplify‐and‐forward relaying cooperative vehicular networks under physical layer security

AbstractIn this paper, we address the physical layer security of a cooperative vehicular network in the presence of a passive eavesdropper vehicle, where the communication from a fixed source node to a fixed destination node is assisted by an amplify‐and‐forward relay vehicle and by direct link, in two transmission phases. Based on the security of the first transmission phase, we consider two scenarios for the cooperative vehicular networks. In Scenario I, the first phase is secure (ie, the direct link between source and eavesdropper is not available) and the eavesdropping occurs only in the second phase. In Scenario II, the first phase is not secure (ie, the direct link between source and eavesdropper is present) and the eavesdropping occurs during both the first and second phases. We assume that source‐to‐destination, source‐to‐relay vehicle, relay vehicle‐to‐destination, and source‐to‐eavesdropper vehicle channels are modeled as Rayleigh fading, whereas the channel between relay and eavesdropper vehicles is modeled by double‐Rayleigh fading. Under such channel modeling, we deduce the new tight closed‐form expressions for the secrecy outage probability (SOP) under both Scenario I and Scenario II. We also investigate the effective secrecy diversity order in the high main‐to‐eavesdropper ratio (MER) regime. The numerical and simulation results corroborate our theoretical analysis and findings and show the occurrence condition for SOP floor phenomenon and influences of channel conditions and relay and eavesdropper locations on the SOP performance. Our results also reveal that the presence of source‐to‐eavesdropper link has significant impact on the SOP performance and relay location.

Impact of Antenna Selection on Physical‐Layer Security of NOMA Networks

This paper studies the impacts of antenna selection algorithms in decode‐and‐forward (DF) cooperative nonorthogonal multiple access (NOMA) networks, where the secure information from the relay can be overheard by an eavesdropper in the networks. In order to ensure the secure transmission, an optimal antenna selection algorithm is proposed to choose one best relay’s antenna to assist the secure transmission. We study the impact of antenna selection on the system secure communication through deriving the analytical expression of the secrecy outage probability along with the asymptotic expression in the high regime of signal‐to‐noise ratio (SNR) and main‐to‐eavesdropper ratio (MER). From the analytical and asymptotic expressions, we find that the system secure performance is highly dependent on the system parameters such as the number of antennas at the relay, SNR, and MER. In particular, the secrecy diversity order of the system is equal to the antenna number, when the interference from the second user is limited.

Impact of Correlated Fading Channels on Cognitive Relay Networks With Generalized Relay Selection

In this paper, we investigate the secrecy performance of dual-hop decode-and-forward cognitive relay networks taking into account the channel correlation between the main and wiretapping channels. For the enhancement of the secrecy performance, a generalized relay selection scheme is utilized, where the $k$ th strongest relay node is selected based on the main channel. In order to analyze the impact of key parameters on the secrecy performance, we first derive the exact closed-form expression for secrecy outage probability (SOP) of the considered networks. Moreover, to extract deep insights, the asymptotic approximation for SOP in high main-to-eavesdropper ratio (MER) regime is also provided. Our theoretical results as well as simulations demonstrate that: 1) the channel correlation does not affect the achievable secrecy diversity order, but has a positive impact on the secrecy coding gain in high MER regime; 2) the secrecy diversity order is decided by the generalized selection coefficient and the number of relays that can successfully decode the information transmitted from the secondary transmitter; and 3) the total amount of relays cannot influence the secrecy diversity order directly, but has a significant impact on the secrecy coding gain.

Secure Switch-and-Stay Combining (SSSC) for Cognitive Relay Networks

In this paper, we study a two-phase underlay cognitive relay network, where there exists an eavesdropper who can overhear the message. The secure data transmission from the secondary source to secondary destination is assisted by two decode-and-forward (DF) relays. Although the traditional opportunistic relaying technique can choose one relay to provide the best secure performance, it needs to continuously have the channel state information (CSI) of both relays, and may result in a high relay switching rate. To overcome these limitations, a secure switch-and-stay combining (SSSC) protocol is proposed where only one out of the two relays is activated to assist the secure data transmission, and the secure relay switching occurs when the relay cannot support the secure communication any longer. This security switching is assisted by either instantaneous or statistical eavesdropping CSI. For these two cases, we study the system secure performance of SSSC protocol, by deriving the analytical secrecy outage probability as well as an asymptotic expression for the high main-to-eavesdropper ratio (MER) region. We show that SSSC can substantially reduce the system complexity while achieving or approaching the full diversity order of opportunistic relaying in the presence of the instantaneous or statistical eavesdropping CSI.

Physical layer security via maximal ratio combining and relay selection over Rayleigh fading channels

In this paper, the impact of both maximal ratio combining (MRC) and relay selection on the physical layer security in wireless communication systems is investigated by analyzing critical issues such as the probability characteristics of the legitimate receiver (Bob) and malicious eavesdropper (Eve)s end-to-end signal-to-noise ratio (SNR), the secrecy outage probability and the average secrecy channel capacity over Rayleigh fading Channel, etc. Unlike the conventional physical layer security schemes, we assume that Bob receives its data from both the relay and the source via cooperative relay, provided that MRC is employed at the receiver. Particularly, compared to the conventional MRC methods, the proposed method is capable of achieving a higher spatial diversity order by performing relay selection, as validated by performing the theoretical analysis as well as numerical simulation. Furthermore, the closed-form expressions in terms of secrecy outage probability and average secrecy capacity are all consistent with the numerical results. Finally, the proposed scheme may be substantially affected by a number of parameters such as the number of relays, the SNR of links and the ratio of main-to-eavesdropper ratio (MER) $\lambda_{\rm ME}$.