This paper investigates the covertness and reliability of unmanned aerial vehicle (UAV) relay communications assisted by a friendly jammer in the presence of co-channel interference (CCI). In the considered scenario, communication from a source to a destination is relayed by a UAV, while a malicious node attempts to monitor the transmission behaviors of both the source and the UAV. To enhance the system’s covertness, we propose a friendly jammer aided covert communication (FJACC) scheme, which leverages a friendly jammer to degrade the detection capability of the malicious monitoring node by sending artificial noise. We analyze the covertness and reliability of the FJACC scheme by deriving closed-form expressions of the outage probability and detection error probability under CCI, considering that the wireless channels are characterized by Nakagami-mfading for UAV-to-ground links and Rayleigh fading for terrestrial links. Numerical results confirm the superior covertness of the proposed FJACC scheme over traditional non-friendly jammer aided transmission scheme. Furthermore, increasing the number of co-channel interferers or their transmit power exhibits a dual effect: it enhances covertness at the expense of reliability.

This paper studies the physical-layer security (PLS) for an unmanned aerial vehicle (UAV)-aided non-orthogonal multiple access (NOMA) network, where transmissions from a base station (BS) to a trusted near user (TNU) and an untrusted far user (UFU) are assisted by an UAV relay in the face of multiple non-colluding external eavesdroppers (Es). The traditional strategies such as artificial noise-aided friendly jammer (TAN-FJ), artificial noise with non-friendly jammer (TAN-NFJ), and reconfigurable intelligent surface (RIS)-aided schemes fail to simultaneously guarantee the secrecy for both TNU and UFU, thus how to guarantee the PLS for NOMA users becomes an urgent issue to be solved. In this context, we propose an artificial noise (PAN) scheme aided with digital network coding (DNC). Specifically, the artificial noise signals generated by UAV are resorted to encrypt confidential signals with the assistance of DNC, which realizes one-time pad, thus the PLS of TNU and UFU can be ensured. We resort security-reliability tradeoff (SRT) as a metric to evaluate the PLS for our proposed PAN scheme. Hence, the exact and asymptotic expressions of outage probability (OP) and intercept probability (IP) are derived to quantify the reliability and security. Moreover, numerical simulations validate the correctness of our theoretical results and reveal that: 1) the PAN scheme enhances the SRT performance of near user compared to the TAN-FJ, TAN-NFJ, and RIS-aided schemes, while far user by the PAN scheme achieves almost the same SRT performance as the TAN-FJ scheme and significantly better performance than the TAN-NFJ and RIS-aided schemes, which indicates that the PAN scheme realizes the fairness of secrecy transmissions for NOMA users; 2) the SRT performance of TNU benefits from multiple antennas at BS and UAV, which has ignorable effect on the SRT performance of UFU; 3) the antenna number at UAV has more obvious impact on the SRT of TUN than the antenna number at BS.

This article studies the secrecy performance for a dual-hop nonorthogonal multiple access (NOMA)-aided unmanned aerial vehicle (UAV) network in the face of a passive untrusted far user (UFU). A new artificial noise (AN) scheme is proposed, where AN generated in the first hop can be used to encrypt confidential signals by XOR operation in the second hop. Based on the proposed AN (PAN) scheme, we analyze the exact and asymptotic outage probabilities (OPs) for both NOMA users and intercept probability (IP) for trusted near user (TNU). Simulation results verify the correctness of our theoretical analysis and demonstrate that the PAN scheme significantly improves the security for TNU at the cost of negligible reliability of UFU compared to the benchmark schemes.

This paper studies the optimization of reconfigurable intelligent surface (RIS)-assisted unmanned aerial vehicle (UAV)-enabled Internet of Things (IoT) communication networks. In this framework, a rotary-wing UAV is dispatched to collect data form multiple ground IoT devices, leveraging the signal enhancement capabilities of an RIS to improve communication efficiency. We aim to enhance the overall energy efficiency (EE), taking into account both the system transmission rate and UAV propulsion power consumption, while satisfying the UAV initial/final position constraints, transmit power limits, and RIS unit-modules phase shift requirements. To achieve this goal, we first establish a closed-form analytical model for the EE of RIS-assisted UAV-enabled IoT wireless systems. Based on this model, we subsequently formulate the EE maximization (EEM) problem by jointly optimizing time allocation, transmit power control, RIS reflection coefficients, and UAV trajectory. Due to the non-convex nature of the proposed EEM problem, we decompose it into three subproblems: 1) RIS phase shift optimization with given resource allocation and UAV trajectory, 2) time and power allocation under fixed UAV trajectory and RIS configuration, and 3) UAV trajectory design based on provided resource allocation and RIS parameters. Particularly, the optimal phase shift solution is derived in a closed form to ensure phase alignment of signals from multiple transmission paths, while the non-convex resource allocation subproblem is solved through introducing relaxation variables. For UAV trajectory design, a hybrid optimization strategy combing Dinkelbach’s method and successive convex approximation approach is adopted to transform the non-convex EE optimization problem into a convex one. Numerical simulations demonstrate that the proposed EEM scheme obtains superior EE performance compared to benchmarks with fixed trajectory or without RIS deployment.

For an uncrewed aerial vehicle (UAV)-aided energy-harvesting non-orthogonal multiple access (EH-NOMA) network, where an untrusted far user (UFU) overhears the confidential transmissions from base station (BS) to the trusted near user (TNU), how to ensure the security of TNU and achieve the reliability of UFU becomes an open issue. The traditional artificial noise (TAN) scheme just guarantees the security of TNU without focusing on the reliability of UFU, while the non-artificial noise (NAN) scheme only ensures the reliability of UFU but sacrifices the security of TNU. Thus, the TAN and NAN schemes are unable to guarantee the fairness between TNU and UFU. To this end, we employ digital network coding to encrypt confidential signals with artificial noise signals, and the proposed artificial noise (PAN) scheme not only protects the confidential transmissions of TNU but also guarantees the reliability of UFU. We use security-reliability tradeoff (SRT) and interference-reliability tradeoff (IRT) to evaluate the performance of TNU and UFU, respectively. Additionally, we derive the exact and asymptotic expressions of outage probabilities for both TNU and UFU, and the intercept probability for TNU. Numerical results verify the accuracy of our theoretical results and demonstrate that: 1) the SRT and IRT performance of the PAN scheme is better than that of the TAN and NAN schemes; 2) the PAN scheme achieves better secrecy for TNU compared to the TAN scheme. Meanwhile, the reliability of UFU in the PAN scheme is almost the same as the NAN scheme, indicating the PAN scheme simultaneously realizes the security of TNU and the reliability of UFU and the fairness of NOMA users is achieved by the PAN scheme.

This article investigates physical-layer security (PLS) for an energy-harvesting cognitive network with nonorthogonal multiple access (EHCN-NOMA), where a cognitive base station (CBS) communicates with two cognitive users named cognitive near user (CNU) and cognitive far user (CFU) by adopting the NOMA principle under an active or passive eavesdropper (Eve) attack. By means of energy harvesters, the CBS collects the radio frequency energy from the primary source (PS) by a time-switching protocol; meanwhile, the cognitive transmit power is limited by the interference threshold of primary destination (PD) to guarantee the Quality of Service (QoS) of primary transmissions. To evaluate the impact of active and/or passive eavesdroppings on system performance, we derive closed-form expressions in terms of outage probabilities (OPs), intercept probabilities (IPs), as well as effective secrecy throughputs (ESTs). The numerical results verify the correctness of our theoretical derivations and confirm that there exists a tradeoff between security and reliability for the EHCN-NOMA transmissions. Moreover, the EST improvement depends on the competition between security and reliability. Furthermore, the maximum EST performance can be achieved for both eavesdropping scenarios by adjusting the time allocation between that of the energy transfer phase and the information transmission phase.

This letter investigates secrecy performance for cognitive transmissions, where a secondary user (SU) shares same spectrum with a primary user (PU) simultaneously ensuring the Quality of Service (QoS) of primary transmissions. Additionally, an eavesdropper (Eve) overhears cognitive transmissions from SU to base station (BS). To against eavesdropping attacks, a novel artificial noise-aided rate splitting (ANRS) scheme is proposed, where PU emits artificial noise to confuse Eve and SU adopts rate splitting (RS). The numerical results of secrecy outage probability indicates that the ANRS scheme achieves better secrecy performance than that of AN without RS (ANWRS) and of RS without AN (RSWAN) schemes.

This paper investigates the physical layer security for a distributed antenna system, where a base station (BS) equipped with multiple distributed antennas transmits signals to a legitimate user (U) through an opportunistic antenna. Meanwhile, multiple non-colluding eavesdroppers (Es) attempt to tap the information transmission between the BS and U. To enhance the physical layer security, a friendly jammer (J) is employed to create a potential interference to Es by emitting artificial noise. However, since U is not aware of the information sent by J, it can be affected by the interference. In this context, this paper proposes adaptive jamming (AJ) scheme and interference cancellation (IC) scheme to mitigate the interference’s impact on U and consequently improve secrecy performance. Specifically, the AJ scheme avoids interference from having a negative effect on the system security by setting an interference threshold, activating the jammer only when the interference to U is below the threshold value. By contrast, the IC scheme designs an advanced special signal to eliminate the interference from J to U. For comparison, we present conventional non-jammer (NJ) scheme as a benchmark. Exact and asymptotic secrecy outage probability expressions for NJ, AJ, and IC schemes are derived over Nakagami-mfading channels. Numerical results show that the proposed AJ and IC schemes perform better than NJ scheme in terms of secrecy outage probability. Additionally, the physical layer security of all schemes can be improved by increasing the number of distributed antennas.

In this study, the authors investigate the employment of transmit antenna selection ( TAS ) against eavesdropping in cognitive radio systems, where a cognitive source (CS) node transmits to a cognitive destination (CD) node in the face of an eavesdropper, each equipped with multiple antennas. The authors derive a closed‐form expression of secrecy outage probability for the proposed TAS scheme. For the purpose of comparison, the authors also study the random antenna selection (RAS) as a baseline. Moreover, the secrecy diversity orders of TAS and RAS are analysed to provide an intuitive insight into the effect of the number of antennas on the secrecy outage performance. It is of interest to observe that the secrecy diversity order of TAS is the product of number of transmit antennas at CS and receive antennas at CD and the secrecy diversity order achieved by RAS scheme is the number of receive antennas at CD, which both have nothing to do with the number of antennas at eavesdropper. Finally, the simulation results validate the authors’ theoretical results and the proposed TAS outperforms the conventional RAS in terms of secrecy outage probability.