Jamming antenna selection (JAS) serves as a low-complexity approach to enhance covert communication in Internet of Things (IoT) networks subject to stringent energy and computational limitations. Unlike conventional JAS strategies that assume a fully cooperative jammer selecting a single antenna for artificial noise transmission, this work investigates the optimal number of selected jamming antennas to maximize covert performance with a limited-cooperation jammer. In the considered scenario, the jammer does not provide the necessary cooperation, which prevents the legitimate receiver from acquiring the jammer–receiver channel state information (CSI). According to the degree of CSI availability at the jammer, two practical JAS schemes, random JAS (RJAS) and minimum JAS (MJAS), are investigated to effectively impair the warden’s detection performance. Closed-form expressions are derived for the warden’s expected minimum detection error probability and the legitimate receiver’s transmission outage probability, with the latter evaluated under interference-limited conditions. Leveraging these results, an optimization framework is developed to jointly determine the transmit power, transmission rate, and number of selected jamming antennas to maximize the effective covert rate. Numerical results illustrate that the effective covert rate under the RJAS strategy increases monotonically with the number of selected antennas, whereas the effective covert rate under the MJAS strategy is maximized when selecting two antennas. Both theoretical analysis and simulation results validate the effectiveness of the proposed schemes and highlight the significant covert performance gains achieved by employing multiple jamming antennas in IoT networks with limited cooperation.
Jamming antenna selection (JAS) serves as a low-complexity approach to enhance covert communication in Internet of Things (IoT) networks subject to stringent energy and computational limitations. Unlike conventional JAS strategies that assume a fully cooperative jammer selecting a single antenna for artificial noise transmission, this work investigates the optimal number of selected jamming antennas to maximize covert performance with a limited-cooperation jammer. In the considered scenario, the jammer does not provide the necessary cooperation, which prevents the legitimate receiver from acquiring the jammer–receiver channel state information (CSI). According to the degree of CSI availability at the jammer, two practical JAS schemes, random JAS (RJAS) and minimum JAS (MJAS), are investigated to effectively impair the warden’s detection performance. Closed-form expressions are derived for the warden’s expected minimum detection error probability and the legitimate receiver’s transmission outage probability, with the latter evaluated under interference-limited conditions. Leveraging these results, an optimization framework is developed to jointly determine the transmit power, transmission rate, and number of selected jamming antennas to maximize the effective covert rate. Numerical results illustrate that the effective covert rate under the RJAS strategy increases monotonically with the number of selected antennas, whereas the effective covert rate under the MJAS strategy is maximized when selecting two antennas. Both theoretical analysis and simulation results validate the effectiveness of the proposed schemes and highlight the significant covert performance gains achieved by employing multiple jamming antennas in IoT networks with limited cooperation.
In this paper, we investigate covert communications in data collected IoT with NOMA, where the paired sensor nodes Smand Sntransmit covert messages to a legitimate receiver (Bob) in the presence of a Warden (Willie). To confuse the detection at Willie, an extra multi-antenna friendly jammer (Jammer) has been employed to transmit artificial noise (AN) with random power. Based on the CSI of Willie is available or not at Jammer, three AN transmission schemes, including null-space artificial noise (NAN), transmit antenna selection (TAS), and zero-forcing beamforming (ZFB), are proposed. Furthermore, the closed-form expressions of expected minimum detection error probability (EMDEP) and joint connection outage probability (JCOP) are derived to measure covertness and reliability, respectively. Finally, the maximum effective covert rate (ECR) is obtained with a given covertness constraint. The numerical results show that ZFB scheme has the best maximum ECR in the case of the number of antennas satisfies N > 2, and the same maximum ECR can be achieved in ZFB and NAN schemes with N =3D 2. Moreover, TAS scheme also can improve the maximum ECR compared with the benchmark scheme (i.e., signal-antenna jammer). In addition, a proper NOMA node pairing can further improve the maximum ECR.
This article investigates covert communications in a multirelay Internet of Things (IoT) system with multiple energy harvesting jammers, where a transmitter (Alice) attempts to covertly transmit confidential messages to its destination (Bob) through relay forwarding, while a warden (Willie) detects the existence of Alice’s transmission. Specifically, we employ a harvesting-then-jamming protocol with which the jammers first harvest energy from Alice and then send jamming signals to interfere with Willie’s detection. We propose a relay and jammer selection strategy, namely quality of service (QoS)-aware selection, and use the random selection strategy as a comparison strategy. Under these two selection strategies, we derive the optimal detection threshold and minimum detection error probability at Willie, respectively. We then model the covert throughput performance and obtain the maximum covert throughput by jointly optimizing covert transmit power and jamming transmit power. Extensive numerical results are provided to illustrate the impacts of system parameters on covert throughput performance.
Covert communications can hide confidential signals in environmental noise to avoid being detected and provide comprehensive security for wireless transmissions. However, there still exist significant risks in wireless transmission once being detected. In this letter, we propose a more secure covert scheme, where a multiple antennas transmitter, assisted by a multi-antenna UAV jammer, maximizes the covert secrecy rate under the scenarios of both correct and incorrect detection by a warden with both error detection probability and eavesdropping rate limitations satisfied. The transmitter and jammer adopt maximum ratio transmission (MRT) and zero-forcing, respectively, to maximize the transmission rate and minimize the interference at the legitimate receiver. First, we analyze the monotonicity of error detection probability to determine the optimal power detection threshold and the corresponding smallest error detection probability. Then, under this worst case, we jointly optimize the transmit and jamming power to maximize the covert secrecy rate while guaranteeing the covert and eavesdropping limits meet their requirements, respectively. Finally, simulation results are presented to prove the correctness of the theoretical conclusion and evaluate the effectiveness of our proposed scheme.
This paper adopts the antenna selection technique to enhance the covert rate in a wireless communication network comprised of a source, a destination , an external jammer and an eavesdropper. In the covert communication, the level of transmit power is low and hence a source with multiple antennas can be adopted to send the information toward the single antenna destination while concurrently, the jammer transmits an artificial noise signal. For this system model, we consider a scenario where the source is forced to select one or several of its antennas to transmit its confidential information due to its limited RF chains. Furthermore, we consider two different jamming scenarios to support our covert communication: 1) The destination is unable to cancel the jamming signal, 2) The destination can subtract the jamming signal. For such a communication network, our aim is to maximize the covert rate subject to power constraint and covert communication requirement. In the first scenario, the optimization problem is non-convex, and hence, it can be solved through using Difference of Convex function (DC) method while the optimization problem of the second scenario is intrinsically convex. Our numerical results show that the higher the number of selected antennas at the transmitter, the higher the covert rate will be achieved.
With the great-leap-forward development of Internet of Things (IoT), it is extremely important to study secure wireless transmission for IoT systems. A cooperative jamming (CJ) strategy has been extensively studied to enhance physical layer security in IoT systems. However, CJ's secrecy performance has not been well studied in the scenario of collusive eavesdroppers. In this paper, we propose a CJ scheme for IoT systems to fight against multiple passive and collusive eavesdroppers of unknown channel state information. Considering nodes with multi-antenna in an IoT system, we design beamforming vectors to maximize signal-to- interference-plus-noise ratio (SINR) of the wireless link from a controller (transmitter) to an actuator (receiver). Under the worst-case assumption that eavesdroppers can aggregate all signals to enhance their eavesdropping abilities, we derive the closed- form expressions of the secrecy outage probability (SOP) with and without CJ. In addition, we employ a strict mathematical asymptotic analysis to provide insights into the effects of various system parameters on the SOP. Numerical results verify that the CJ scheme can effectively prevent eavesdropping and the effects of system parameters on SOP is consistent with theoretical analytical results.
The cell-free (CF) network architecture has promising applications in Internet of Things (IoT) networks due to its dynamic and adaptive nature in resource allocation. However, due to the openness of wireless channels and the information interaction of sensitive data, the security issues of CF IoT networks have become more severe, especially in the case of powerful opponents. In this article, a high-level secure transmission technique is utilized to protect the privacy of users, which is called covert communication. Specifically, in the CF IoT network conceived, one IoT device secretly transmits sensitive information to an access point (AP) under the cover of a selected jammer to avoid being detected by other curious IoT devices, which are regarded as potential eavesdroppers (Eves) and determined by the central processing unit (CPU) based on greedy degree. Then, we analyze the joint impact of jamming and greedy degree on the detection error probability (DEP) for Eve, and determine Eve’s minimum DEP as well as the corresponding optimal threshold. To enhance energy efficiency while ensuring communication security, three jamming scheduling schemes have been proposed, namely, the jamming scheduling for both the receiver (Bob) and Eve (JSBE), the jamming scheduling for Eve (JSE), and the jamming scheduling for Bob (JSB). Numerical results indicate that greedy degree dominates the average minimum DEP for Eve when IoT devices tend to be lightweight. Furthermore, JSBE scheme demonstrates superiority in terms of covert rate, covert outage probability (COP), and covert energy efficiency (CEE), which provides an effective solution for high-security transmission of energy-constrained nodes in CF IoT networks.