In this work, by considering a variety of realistic hardware impairments, we aim to enhance the security of a cooperative relaying network, where a source intends to transmit its confidential information to a destination in the presence of a group of untrusted amplify-and-forward relays, as potential eavesdroppers (Eves), and an entirely passive multiple-antenna aided Eve. Our goal is to safeguard the information against these two types of eavesdropping attacks, while simultaneously relying on the untrusted relays to boost both the security and reliability of the network. To reach this goal, we propose a novel joint cooperative beamforming, jamming and power allocation policy to safeguard the confidential information while concurrently achieving the required quality-of-service at the destination. We also take into account both the total power budget constraint and a practical individual power constraint for each node. Our optimization problem can be split into two consecutive sub-problems. In the first sub-problem, we are faced with a non-convex problem which can be transformed into the powerful difference of convex (DC) program. A low-complexity iterative algorithm is proposed to solve the DC program, which relies on the constrained concave-convex procedure (CCCP). We further introduce a novel initialization method, which is based on a feasible point of the original problem obtained from a novel iterative feasibility search procedure, rather than an arbitrary (infeasible) point as in the conventional CCCP. The second sub-problem of our optimization problem is a convex optimization problem and can be solved efficiently adopting the classic interior point method. The numerical results provided illustrate that although the trusted relaying scenario outperforms the untrusted relaying for small and medium total power budgets, however, by increasing the total power budget, the secrecy performances of both the trusted and untrusted relaying converge to the same. Additionally, by equally sharing the total impairments at the relays between the transmitter and the receiver the best secrecy performance is presented. INDEX TERMS Physical layer security, untrusted relay, passive eavesdropper, hardware impairments, cooperative beamforming and jamming, optimal power allocation.

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This paper investigates the physical layer security 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. Taking into account the hardware impairments, and power budget constraints, this paper presents a novel approach to jointly optimize relay beamformer and transmit powers aimed at maximizing average secrecy rate (ASR). 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. 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 improve the ASR 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.