Untrusted Relay Research Articles

Secrecy rate maximization for hardware impaired untrusted relaying network with deep learning

This paper investigates the physical layer security (PLS) design of an untrusted relaying network where the source node coexists with a multi-antenna eavesdropper (Eve). While the communication relies on untrustworthy relay nodes to increase reliability, we aim to protect the confidentiality of information against combined eavesdropping attacks performed by both untrusted relay nodes and Eve. Considering the hardware impairments (HIs), both total power budget constraint for the whole network and the individual power constraint at each node, this paper presents a novel approach to jointly optimize relay beamformer and transmit powers aiming at maximizing average secrecy rate (ASR). To safeguard the first cooperative phase, destination-aided cooperative jamming (DACJ) is employed, while for the second phase, the relay beamformer is adjusted. The resultant optimization problem is non-convex, and a suboptimal solution is obtained through the sequential parametric convex approximation (SPCA) method. In order to prevent any failure due to infeasibility, we propose an iterative initialization algorithm to find the feasible initial point of the original problem instead of an arbitrary point, as in the conventional SPCA. To satisfy low-latency as one of the main key performance indicators (KPI) required in beyond 5G (B5G) communications, a computationally efficient data-driven approach is developed exploiting a deep learning model to evaluate the proposed scheme while the computational burden is significantly reduced. Simulation results assess the effect of different system parameters on the ASR performance as well as the effectiveness of the proposed deep learning solution in large-scale cases.

Free Space Measurement Device Independent Quantum Key Distribution with Modulating Retro-Reflectors under Correlated Turbulent Channel.

Modulating retro-reflector (MRR), originally introduced to support laser communication, relieves most of the weight, power, and pointing requirements to the ground station. In this paper, a plug-and-play measurement device independent quantum key distribution (MDI-QKD) scheme with MRR is proposed not only to eliminate detector side channels and allow an untrusted satellite relay between two users, but also to simplify the requirements set-ups in practical flexible moving scenarios. The plug-and-play architecture compensates for the polarization drift during the transmission to provide superior performance in implementing the MDI-QKD on a free-space channel, and the MRR device is adopted to relax the requirements on both communication terminals. A double-pass correlated turbulent channel model is presented to investigate the complex and unstable channel characteristics caused by the atmospheric turbulence. Furthermore, the security of the modified MDI-QKD scheme is analyzed under some classical attacks and the simulation results indicate the feasibility under the situation that the system performance deteriorates with the increase of fading correlation coefficient and the turbulence intensity, which provides a meaningful step towards an MDI-QKD based on the moving platforms to join a dynamic quantum network with untrusted relays.

Trust-aware buffer-aided relay selection for secure communications in cooperative wireless systems

Cooperative wireless networks have been facing security challenges due to the inherent openness of wireless channels. Previous studies on the physical layer security (PLS) of cooperative networks mainly focus on scenarios with only trusted relays. In practice, however, untrusted relays may exist in the network and such relays may refuse to cooperate or even work as a helper of an eavesdropper for packets eavesdropping/interception. To address this issue, we consider in this paper a cooperative wireless network with untrusted relays and a passive eavesdropper attempting to wiretap packets transmitted in the network. To select a secure and trusted relay, we first propose two buffer-aided relay selection schemes, one for perfect eavesdropper channel state information (CSI) case and another for no eavesdropper CSI case. We then conduct theoretical analysis to derive the models for the performance metrics of secrecy outage probability (SOP) and expected queuing delay. Finally, simulation and numerical results are provided for the validation of our theoretical models. The results indicate that our proposed schemes can outperform the typical max-ratio scheme under perfect eavesdropper CSI case and can outperform the max-link and the max-max relay selection schemes under no eavesdropper CSI case in terms of the SOP and expected queuing delay.

Hybrid protocol for wireless-powered untrusted relay networks with imperfect channel reciprocity

This work investigates the security issue of the energy-constrained untrusted relay network with imperfect channel reciprocity, where the relay without the built-in power supply can only scavenge energy from radio-frequency signals radiated by the source and destination. A hybrid power-splitting (PS)- and time-switching (TS)-based relaying (HPTR) protocol is presented to improve the degraded secrecy performance due to the incomplete self-interference cancellation at the destination. To evaluate the secrecy throughput (ST) of the studied system, the analytical expression of the secrecy outage probability under the delay-limited transmission mode and the closed-form lower bound of the ergodic secrecy capacity under delay-tolerant transmission mode are derived. Both linear and nonlinear models for the energy harvester at the relay are compared. The optimal PS and TS ratios are evaluated numerically. The theoretical derivations are validated by numerical results, revealing that the residual jamming has a negative effect on the secrecy performance of untrusted relay networks, which can be alleviated by the HPTR protocol. Besides, we compare the ST performance of the HPTR protocol with that of the PS and TS relaying schemes, and the results show that the HPTR protocol outperforms both PS and TS relaying protocols in terms of the ST.

Secure NOMA and OMA coordinated transmission schemes in untrusted relay networks

Secure NOMA and OMA coordinated transmission schemes in untrusted relay networks

On the performance of physical layer security in virtual full-duplex non-orthogonal multiple access system

This paper investigates physical layer security analysis of cooperative non-orthogonal multiple access (NOMA) communication system. A virtual full-duplex (VFD) relaying scheme with an untrusted amplify-and-forward (AF) half-duplex (HD) relay and a trusted decode-and-forward (DF) HD relay is used in this system to improve the spectral efficiency. In order to prevent the untrusted relay from eavesdropping, a simple and practical cooperative jamming scheme is designed to confuse the untrusted relay. The exact expressions of effective secrecy throughput (EST) for NOMA users and approximate expression of EST for non-NOMA user are derived. All theoretical results are validated by numerical simulations which demonstrate that the proposed VFD-NOMA scheme is superior to existing HD-NOMA scheme in cooperative system and jamming plays an important role for obtaining acceptable EST. In addition, simulation results shows that the best secrecy performance highly depends on the system parameters such as transmit powers and jamming signal power.

Security for Two-Way Untrusted Relay against Constant and Reactive Jamming with Fixed Signals

Active attacking in physical-layer security has not been significantly studied while potentially causing serious consequences for the legitimate networks. In this paper, we propose a novel method to estimate and remove the jamming signals from multiple multi-antenna jammers in a two-way relay network with multi-antenna legitimate and relay nodes. We carefully consider the signals in the time slots in order to exploit the repetition of the signals and design the transmitted signals which can work in different cases. The numerical results show that the secrecy maximum achievable sum-rate (MASR) at the legitimate nodes is higher than that of the conventional method when considering the affect of transmit SNR; the number antennas at the legitimate and relay nodes; normalized distance between one legitimate node and the relay; and the vertical coordinate of the relay.

Overloaded Wireless MIMO Switching for Information Exchanging through Untrusted Relay in Secure Wireless Communication

Overloaded Wireless MIMO Switching for Information Exchanging through Untrusted Relay in Secure Wireless Communication

Hybrid Trusted/Untrusted Relay-Based Quantum Key Distribution Over Optical Backbone Networks

Quantum key distribution (QKD) has demonstrated a great potential to provide future-proofed security, especially for 5G and beyond communications. As the critical infrastructure for 5G and beyond communications, optical networks can offer a cost-effective solution to QKD deployment utilizing the existing fiber resources. In particular, measurement-device-independent QKD shows its ability to extend the secure distance with the aid of an untrusted relay. Compared to the trusted relay, the untrusted relay has obviously better security, since it does not rely on any assumption on measurement and even allows to be accessed by an eavesdropper. However, it cannot extend QKD to an arbitrary distance like the trusted relay, such that it is expected to be combined with the trusted relay for large-scale QKD deployment. In this work, we study the hybrid trusted/untrusted relay based QKD deployment over optical backbone networks and focus on cost optimization during the deployment phase. A new network architecture of hybrid trusted/untrusted relay based QKD over optical backbone networks is described, where the node structures of the trusted relay and untrusted relay are elaborated. The corresponding network, cost, and security models are formulated. To optimize the deployment cost, an integer linear programming model and a heuristic algorithm are designed. Numerical simulations verify that the cost-optimized design can significantly outperform the benchmark algorithm in terms of deployment cost and security level. Up to 25% cost saving can be achieved by deploying QKD with the hybrid trusted/untrusted relay scheme while keeping much higher security level relative to the conventional point-to-point QKD protocols that are only with the trusted relays.

The Research of NOMA-MEC Network based on Untrusted Relay-Assisted Transmission in Power Internet of Things

Mobile edge computing provides a promising architecture for the computing of power Internet of Things terminal equipment, which can effectively solve the problems of insufficient computing power and energy-limitation of terminal equipment. In addition, relay-assisted transmission is adopted because the equipment may be far away from the MEC server. However, relay may be attacked by malicious users and become untrusted relay. Therefore, destination-assisted jamming is proposed to improve the security performance of offload computing. In order to improve spectrum utilization, non-orthogonal multiple access technology is used to transmission. An alternate iterative algorithm is proposed to jointly optimize the power allocation and offloading time to maximize security energy efficiency. The simulation results verify the effectiveness of the proposed method.

Secure Computation-and-Forward With Linear Codes

We discuss secure transmission via an untrusted relay when we have a multiple access phase from two nodes to the relay and a broadcast phase from the relay to the two nodes. To realize the security, we construct a code that securely transmits the modulo sum of the messages of two nodes via a multiple access channel. In this code, the relay cannot obtain any information with respect to the message of each node, and can decode only the modulo-sum of the messages of the two nodes. Our code is constructed by simple combination of an existing linear code and universal2 hash function.

Secure and Energy-Efficient Precoding for MIMO Two-Way Untrusted Relay Systems

This paper focuses on the multiple-input-multiple-output (MIMO) two-way relay system with an untrusted relay and investigates its secure and energy-efficient precoding design issue based on the physical layer security technology. We first provide theoretical modeling for the index of secrecy energy efficiency (SEE) and formulate the optimal precoding design for SEE maximization (SEEM) as a high-dimensional non-convex programming problem. By exploring the techniques like fractional programming, alternate optimization and semi-definite programming, we then develop a hierarchical theoretical framework to solve the SEEM problem and thus to identify the optimal precoding designs for the source and relay. Furthermore, we demonstrate the proposed theoretical framework is also applicable to the problem of precoding design for secrecy sum rate maximization. Finally, with the help of generalized singular value decomposition, we propose a sub-optimal relay precoding design scheme with significantly lower computational complexity. Extensive numerical results provided in the paper indicate that the proposed schemes can remarkably improve the SEE performance in MIMO two-way untrusted relay systems.

Secure Resource Allocation for Cooperative OFDMA System With Untrusted AF Relaying

In this paper, we consider a cooperative orthogonal frequency division multiple access (OFDMA) system, where a source communicates with multiple users with the help of an untrusted relay. Since we assume no direct links between source and users because of the shadowing effect, the positive secrecy rate of the system cannot be obtained directly. Addressing this issue, we employ the user-aided cooperative jamming method to improve the secrecy performance. With the aim of maximizing the weighted sum secrecy rate, we formulate a joint resource allocation problem of power allocation, subcarrier assignment and subcarrier pairing. By using the alternative optimization and the Lagrange dual method, we solve this non-convex problem efficiently. Furthermore, to reduce the calculation complexity, we propose two suboptimal algorithms. Numerical results are presented to demonstrate the advantage of the proposed algorithms compared with the benchmarks on the secrecy performance. Moreover, we show that our proposed algorithms are more sensitive to user priority weights than benchmarks.

Secrecy Performance of a Multi-NOMA-MIMO System in the UEH Relaying Network Using the PSO Algorithm

In this paper, we investigate the secrecy performance of the nonorthogonal multiple access (NOMA) system in an untrusted relaying energy harvesting (UEH) network with the multiple-input multiple-output (MIMO) architecture using the maximum ratio transmission (MRT) and maximal ratio combining (MRC) techniques. In this network, a source communicates with users with the help of a relaying network composed of multiple untrusted components using the amplify-and-forward (AF) protocol. These untrusted relay nodes are equipped with a single antenna and employ the power-splitting (PS) protocol to harvest energy from received signals. Moreover, to improve the secrecy outage performance and protect the confidential information from the untrusted relaying network, the source acts as the jammer to generate artificial noise (AN). To evaluate the secrecy performance of each user and the overall system, we derive the closed-form expressions of the secrecy outage probability (SOP) over the Rayleigh fading channels and use a Monte Carlo simulation to verify the accuracy of these analytical results. Moreover, to analyze the secrecy data rate, the maximization problem of the sum secrecy rate (SSR) of the system is solved by applying the particle swarm optimization (PSO) algorithm based on power allocation (PA). These results are also validated with the optimal exhaustive search method. Furthermore, we compare the MIMO/NOMA and MIMO/OMA systems and examine the effects of various system parameters to characterize the secrecy effectiveness of both systems.

On secure transmission in hybrid satellite‐terrestrial cooperative network with untrusted energy harvesting relay and imperfect channel estimation

AbstractIn this paper, the security performance of a hybrid satellite‐terrestrial cooperative network (HSTCN) with untrusted energy limited relay and imperfect channel state information (CSI) is investigated. The satellite and terrestrial links are assumed to follow Shadowed‐Rician fading and Rayleigh fading distributions respectively. The amplify‐and‐forward energy‐limited relay node employs power splitting relaying mode to scavenge energy from its received signals. By considering imperfect CSI between the relay and destination link, maximum ratio combining (MRC) and selection combining (SC) diversity schemes are utilized at the destination to enhance the quality of received signal‐to‐noise ratio (SNR) and aid jamming signal to prevent the untrusted relay from intercepting the satellite confidential data. Thus, to evaluate the HSTCN security performance, the exact analytical closed‐form expressions for the security outage probability (SOP) and connectivity outage probability (COP) are derived for each of the diversity combining techniques. Owing to trade‐off between SOP and COP, the effective secrecy throughput (EST) expression is obtained for the considered diversity schemes with a view to examine the security and reliability performance of the concerned system. Moreover, the impact of system parameters such as transmit SNR, channel coefficient, energy harvesting coefficient, and number of antennas are evaluated. In addition, the results reveal that the MRC has better SOP, COP, and EST performance compare with the SC. Also, it is found that the system EST degrades at high transmit SNR when the number of antennas at satellite is higher. The accuracy of the derived analytical expressions is confirmed by using Monte‐Carlo simulations.

Long-Distance Free-Space Measurement-Device-Independent Quantum Key Distribution.

Measurement-device-independent quantum key distribution (MDI-QKD), based on two-photon interference, is immune to all attacks against the detection system and allows a QKD network with untrusted relays. Since the MDI-QKD protocol was proposed, fiber-based implementations aimed at longer distance, higher key rates, and network verification have been rapidly developed. However, owing to the effect of atmospheric turbulence, MDI-QKD over a free-space channel remains experimentally challenging. Herein, by developing a robust adaptive optics system, high-precision time synchronization and frequency locking between independent photon sources located far apart, we realized the first free-space MDI-QKD over a 19.2-km urban atmospheric channel, which well exceeds the effective atmospheric thickness. Our experiment takes the first step toward satellite-based MDI-QKD. Moreover, the technology developed herein opens the way to quantum experiments in free space involving long-distance interference of independent single photons.

Can a multi-hop link relying on untrusted amplify-and-forward relays render security?

Cooperative relaying is utilized as an efficient method for data communication in wireless sensor networks and the Internet of Things (IoT). However, sometimes due to the necessity of multi-hop relaying in such communication networks, it is challenging to guarantee the secrecy of cooperative transmissions when the relays may themselves be eavesdroppers, i.e., we may face with the untrusted relaying scenario where the relays are both necessary helpers and potential adversary. To obviate this issue, a new cooperative jamming scheme is proposed in this paper, in which the data can be confidentially communicated from the source to the destination through multiple untrusted relays. In our proposed secure transmission scheme, all the legitimate nodes contribute to providing secure communication by intelligently injecting artificial noises to the network in different communication phases. For the sake of analysis, we consider a multi-hop untrusted relaying network with two successive intermediate nodes, i.e, a three-hop communications network. Given this system model, a new closed-form expression is presented in the high signal-to-noise ratio (SNR) region for the Ergodic secrecy rate (ESR). Furthermore, we evaluate the high SNR slope and power offset of the ESR to gain an insightful comparison of the proposed secure transmission scheme and the state-of-arts. Our numerical results highlight that the proposed secure transmission scheme provides better secrecy rate performance compared with the two-hop untrusted relaying as well as the direct transmission schemes.

NOMA in Cooperative Communication Systems With Energy-Harvesting Nodes and Wireless Secure Transmission

In this paper, non-orthogonal multiple access (NOMA) in cooperative relay system is considered, where a source node communicates with a pair of energy harvesting (EH) user equipments through a multiple antennas relay node. A hybrid protocol is adopted at the relay, in which if the relay can successfully decode the signals, decode-and-forward (DF) protocol will be adopted to forward the signals to the users. Otherwise, amplify-and-forward (AF) protocol will be implemented. Assuming that the users adopt maximal ratio combining (MRC) to combine the received signals in the two cooperative phases, new explicit analytical expressions for the average sum-rate are derived when the relay works in, 1) AF mode, and 2) DF mode, in two scenarios when one user is the stronger in both cooperation phases, and when an alternative user is stronger in each phase. Then, the investigation is extended to the case where the relay is an untrusted node, and cooperative jamming technique is proposed to degrade the ability of the relay to decode the signals and enforce the relay to operate always in AF mode. For the untrusted relay scenario, new analytical expression for the average secrecy rate is derived. Monte Carlo simulations are provided to validate the analysis. The simulation results reveal that the location of the relay is the key parameter to achieve the best performance.

Secure Communication With Outdated Channel State Information via Untrusted Relay Capable of Energy Harvesting

In this paper, we consider secure communication via a wireless-powered untrusted relay with outdated channel state information (CSI). The low security clearance of the relay means that both the source and destination wish to keep information confidential from it. To prevent the relay from decoding the source information, the destination emits a jamming signal to the relay during data transmission by the source. The wireless-powered relay uses both the data and the jamming signals as valuable sources of energy for the amplify-and-forward relaying process. In addition, it can adopt either a power splitting or a time switching policy to determine the proportions of energy harvesting and information processing. However, when the CSI of the relay-to-destination link is outdated, the destination cannot remove the jamming signal completely from the relaying signal due to imperfect channel reciprocity. To evaluate the effect of outdated CSI on the secrecy performance, we derive the analytical expressions of two performance metrics, outage probability ( $P_{out}$ ) for delay-limited transmission and ergodic secrecy rate ( $\bar{R}$ ) for delay-tolerant transmission. The results of the analysis also allow us to find the jamming power level and energy harvesting ratio to optimize $P_{out}$ and $\bar{R}$ , respectively. Numerical simulations are used to verify the precision of our analysis, and confirm that the proposed secure relaying protocols accomplish near-optimal secrecy performances. Our results indicate that there is a need to reduce the jamming power level to ensure secure communication when the channel is severely outdated, while outdated CSI has a relatively low impact on the energy harvesting ratio.

Open-Destination Measurement-Device-Independent Quantum Key Distribution Network.

Quantum key distribution (QKD) networks hold promise for sharing secure randomness over multi-partities. Most existing QKD network schemes and demonstrations are based on trusted relays or limited to point-to-point scenario. Here, we propose a flexible and extensible scheme named as open-destination measurement-device-independent QKD network. The scheme enjoys security against untrusted relays and all detector side-channel attacks. Particularly, any users can accomplish key distribution under assistance of others in the network. As an illustration, we show in detail a four-user network where two users establish secure communication and present realistic simulations by taking into account imperfections of both sources and detectors.