This paper investigates the effect of untrusted relay on the secrecy outage probability of amplify- and-forward relay networks with the help of direct links and multiple users. We consider three selection criteria which are based on the direct and relaying link. The impacts of both the direct and relaying links on SOP performance is studied by deriving the closed-form analytical SOP as well as the asymptotic expressions. Simulation results are provided to confirm the theoretical analysis. It can be found that the diversity order of optimal selection criterion is equal to the number of users, while the diversity order of the sub-optimal criterion based on relaying links is equal to one.
This paper investigates the effect of untrusted relay on the secrecy outage probability of amplify- and-forward relay networks with the help of direct links and multiple users. We consider three selection criteria which are based on the direct and relaying link. The impacts of both the direct and relaying links on SOP performance is studied by deriving the closed-form analytical SOP as well as the asymptotic expressions. Simulation results are provided to confirm the theoretical analysis. It can be found that the diversity order of optimal selection criterion is equal to the number of users, while the diversity order of the sub-optimal criterion based on relaying links is equal to one.
This paper investigates the secure communications of multiuser untrusted amplify-and-forward relay networks in the presence of direct links. In the considered system, one user is selected among multiple ones for secure transmission to the destination node with the help of an untrusted relay node. To reduce the information leakage to the untrusted relay, the paper considers two selection criteria to select the user based on the direct and the relaying links, respectively. The impact of direct and the relaying link on the system secrecy performance is studied by deriving the close-form ergodic secrecy rate (ESR) as well as the asymptotic expression. From the asymptotic expression, it can be found that the asymptotic ESR increases linearly with the logarithm of the average channel gain ratio of the direct link to the relaying link.
This paper proposes relay selection to increase the physical layer security in multiuser cooperative relay networks with multiple amplify-and-forward relays, in the presence of multiple eavesdroppers. To strengthen the network security against eavesdropping attack, we present three criteria to select the best relay and user pair. Specifically, criteria I and II study the received signal-to-noise ratio (SNR) at the receivers, and perform the selection by maximizing the SNR ratio of the user to the eavesdroppers. To this end, criterion I relies on both the main and eavesdropper links, while criterion II relies on the main links only. Criterion III is the standard max-min selection criterion, which maximizes the minimum of the dual-hop channel gains of main links. For the three selection criteria, we examine the system secrecy performance by deriving the analytical expressions for the secrecy outage probability. We also derive the asymptotic analysis for the secrecy outage probability with high main-to-eavesdropper ratio. From the asymptotic analysis, an interesting observation is reached: for each criterion, the system diversity order is equivalent to the number of relays regardless of the number of users and eavesdroppers.
This paper studies the physical-layer security of a task-oriented multiuser amplify-and-forward (AF) relay network, operating in environments with multiple eavesdroppers. In the severe communication scenarios, such as urban areas with heavy shadowing or post-disaster zones, the direct communication paths are unavailable and the secure transmission depends solely on trusted relay nodes. To enhance the system secrecy performance, we introduce a relay–user pairing strategy aimed at minimizing the secrecy outage probability (SOP), taking into account the conditions of both legitimate and intercepting channels. Under Rayleigh fading, we derive closed-form SOP expressions and provide an asymptotic analysis that highlights the system’s diversity gain in the high main-to-eavesdropper ratio (MER) regime. Simulations confirm the validity of our theoretical and asymptotic results. Specifically, the analytical SOP exhibits excellent agreement with simulation ones across a wide MER range, confirming the correctness of the derived expressions. Moreover, the asymptotic expressions closely approximate the simulation results when MER exceeds 15 dB, highlighting their effectiveness for performance evaluation in high MER scenarios. Notably, the proposed relay–user selection strategy achieves a significant reduction in SOP compared to random or fixed pairing methods.
We investigate the impact of cochannel interference on the security performance of multiple amplify-and-forward (AF) relaying networks, where N intermediate AF relays assist the data transmission from the source to the destination. The relays are corrupted by multiple cochannel interferers, and the information transmitted from the relays to the destination can be overheard by the eavesdropper. In order to deal with the interference and wiretap, the best out of N relays is selected for security enhancement. To this end, we derive a novel lower bound on the secrecy outage probability (SOP), which is then utilized to present two best relay selection criteria, based on the instantaneous and statistical channel information of the interfering links. For these criteria and the conventional max-min criterion, we quantify the impact of cochannel interference and relay selection by deriving the lower bound on the SOP. Furthermore, we derive the asymptotic SOP for each criterion, to explicitly reveal the impact of transmit power allocation among interferers on the secrecy performance, which offers valuable insights into practical design. We demonstrate that the all selection criteria achieve full secrecy diversity order N, while the proposed two criteria in this paper outperform the conventional max-min scheme.
Impact of Relay’s Eavesdropping on Untrusted Amplify-and-Forward Networks Over Nakagami- m Fading
We investigate the impact of eavesdropping on the secrecy outage performance of dual-hop amplify-and-forward networks with a single untrusted relay, in which cooperative jamming technique is employed at the destination to realize positive secrecy rate. Under Nakagami-m fading channels, we derive tight closed-form and asymptotic expressions for the lower and upper bounds of the secrecy outage probability (SOP). Our results explicitly show that a secrecy diversity order of min(m1, m2/2) in terms of the SOP is achieved, where m1and m2are the respective integer fading parameters of the source-relay and relay-destination links. Afterwards, we propose an asymptotically optimal power allocation (OPA) scheme that minimizes the SOP. Numerical and simulation results show that the proposed OPA offers significant improvement on the SOP performance, especially in the case of m1> m2/2.
In this chapter, we will present criteria for user selection and relay selection to enhance the physical layer security in multiuser multi-relay networks. Specifically, for multiuser networks with multiple amplify-and-forward (AF) relays, we present three criteria to select the best relay and user pair. Criteria I and II study the received signal-to-noise ratio (SNR) at the receivers and perform the selection by maximising the SNR ratio ofthe user to the eavesdroppers. To this end, criterion I relies on both the main and eavesdropper links, while criterion II relies on the main links only. Criterion III is the standard max-min selection criterion, which maximises the minimum of the dual-hop channel gains of main links. For the three selection criteria, we examine the system secrecy performance by deriving the analytical expressions for the secrecy outage probability. We also derive the asymptotic analysis for the secrecy outage probability with high main-to-eavesdropper ratio.