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In this article, we consider the system performance of an energy harvesting (EH) wireless sensor network in terms of reliable communications when subjected to a cooperative jamming attack. A set of strategically located nodes acting as cluster heads (CHs) transfer energy to the wireless sensors within range, forming a cluster. The sensors use this energy to transmit data to the CHs, which, in turn, deliver the information to a base station (BS) using nonorthogonal multiple access. The BS processes the collected information and synchronizes the operation of all CHs. Furthermore, there exist two adversaries, namely, a jamming attacker and an eavesdropper, who cooperate to attack the considered system. To protect against this attack, the CHs should be controlled by suitable power allocation coefficients obtained from the security constraints of the CHs. Using these constraints, closed-form expressions are derived to find the power allocation coefficients that will enable reliable and secure communication. In addition, we propose an interference channel selection policy for the sensor-to-CHs links and CHs-to-BS links to improve the reliability of communication while enhancing energy utilization. Finally, an algorithm for finding the optimal EH time is also proposed.

In this paper, we investigate radio frequency (RF) energy harvesting (EH) in wireless sensor networks (WSNs) using non-orthogonal multiple access (NOMA) uplink transmission with regard to a probable secrecy outage during the transmission between sensor nodes (SNs) and base station (BS) in the presence of eavesdroppers (EAVs). In particular, the communication protocol is divided into two phases: 1) first, the SNs harvest energy from multiple power transfer stations (PTSs), and then, 2) the cluster heads are elected to transmit information to the BS using the harvested energy. In the first phase, we derive a 2D RF energy model to harvest energy for the SNs. During the second phase, the communication faces multiple EAVs who attempt to capture the information of legitimate users; thus, we propose a strategy to select cluster heads and implement the NOMA technique in the transmission of the cluster heads to enhance the secrecy performance. For the performance evaluation, the exact closed-form expressions for the secrecy outage probability (SOP) at the cluster heads are derived. A nearly optimal EH time algorithm for the cluster head is also proposed. In addition, the impacts of system parameters, such as the EH time, the EH efficiency coefficient, the distance between the cluster heads and the BS, and the number of SNs as well as EAVs on the SOP, are investigated. Finally, Monte Carlo simulations are performed to show the accuracy of the theoretical analysis; it is also shown that the secrecy performance of NOMA in RF EH WSN can be improved using the optimal EH time.

In this article, we consider the information leakage and outage probabilities of a multiple-input single-output (MISO) energy-harvesting (EH) Internet of Things (IoT) system in which a multiantenna ground base station (GBS) transmits messages to legitimate IoT destinations (LIDs) with the help of IoT relays (IRs) using non-orthogonal multiple access (NOMA) in the presence of a malicious jammer (MJ) and eavesdroppers (EAVs). The communication protocol is separated into two phases. In the EH phase, the IRs harvest energy from a power beacon (PB). In the information transmission (IT) phase, the communication process is further divided into two subphases: 1) The GBS broadcasts signals to the IRs using NOMA. Simultaneously, the MJ sends interfering signals to attack the IRs while the EAVs steal the confidential signals from the GBS, in a process called a cooperative attack. On the other hand, to protect the legitimate communication, an unmanned aerial vehicle (UAV) is used as a friendly jammer to defend against the EAVs. 2) A selected IR employs the time-switching-based relaying (TSR) technique to forward the received signal to the LIDs using NOMA. Similar to the first subphase, the LIDs are subjected to a cooperative attack, and the UAV attacks the EAVs in return. The secrecy performance of this communication protocol is characterized by deriving expressions for the information leakage probabilities (ILPs) for the LIDs' signals. A UAV altitude optimization algorithm is also proposed to achieve the best possible secrecy performance. Furthermore, we evaluate the system performance by deriving closed-form expressions for the outage probabilities (OPs). Accordingly, an algorithm is proposed to guarantee both the secrecy and system performance (in terms of the ILPs and OPs). Monte Carlo simulations are presented to verify our analytical results.

In this paper, we investigate the physical layer security (PLS) performance for the Internet of Things (IoT), which is modeled as an IoT sensor network (ISN). The considered system consists of multiple power transfer stations (PTSs), multiple IoT sensor nodes (SNs), one legitimate fusion center (LFC) and multiple eavesdropping fusion centers (EFCs), which attempt to extract the transmitted information at SNs without an active attack. The SNs and the EFCs are equipped with a single antenna, while the LFC is equipped with multiple antennas. Specifically, the SNs harvest energy from the PTSs and then use the harvested energy to transmit the information to the LFC. In this research, the energy harvesting (EH) process is considered in the following two strategies: 1) the SN harvests energy from all PTSs, and 2) the SN harvests energy from the best PTS. To guarantee security for the considered system before the SN sends the packet, the SN’s power is controlled by a suitable power policy that is based on the channel state information (CSI), harvested energy, and security constraints. An algorithm for the nearly optimal EH time is implemented. Accordingly, the analytical expressions for the existence probability of secrecy capacity and secrecy outage probability (SOP) are derived by using the statistical characteristics of the signal-to-noise ratio (SNR). In addition, we analyze the secrecy performance for various system parameters, such as the location of system elements, the number of PTSs, and the number of EFCs. Finally, the results of Monte Carlo simulations are provided to confirm the correctness of our analysis and derivation.

In this paper, we investigate the secrecy performance of a Cooperative Cognitive Radio Network (CCRN) in the presence of an eavesdropper (EAV). The secondary users (SUs) are subject to three constraints which include peak transmit power level and interference limitation with respect to the primary user (PU) as well as secrecy outage constraints due to the EAV. Secrecy outage is achieved when the EAV cannot decode the targeted signal, but communications in the secondary network is still possible (non-zero capacity exists). Approximation expressions of the secrecy outage probability and the probability of non-zero secrecy capacity are derived to evaluate the secrecy performance. Monte Carlo simulations are provided to examine the accuracy of the derived approximation expressions. Based on this, power allocation policies for the SUs are derived, satisfying all the constraints while maximizing the secrecy performance as well as the quality of service performance of the secondary network. It can be concluded that with knowledge of the channel state information (CSI) of the EAV it is possible to calculate the optimal value for the secrecy outage threshold of the secondary user (SU) which in turn allows maximizing the secrecy performance. Most interestingly, our numerical results illustrate that the secrecy performance of the system is much improved when the parameters obtained using the CSI of the EAV are calculated optimally. Thence, the system can adjust the power allocation so that no eavesdropping occurs even without reducing quality of service (QoS) performance compared to a network without any EAV.

In this paper, we analyze the secrecy and throughput of multiple-input single-output (MISO) energy harvesting (EH) Internet of Things (IoT) systems, in which a multi-antenna base station (BS) transmits signals to IoT devices (IoTDs) with the help of relays. Specifically, the communication process is separated into two phases. In the first phase, the BS applies transmit antenna selection (TAS) to broadcast the signal to the relays and IoTDs by using non-orthogonal multiple access (NOMA). Here, the relays use power-splitting-based relaying (PSR) for EH and information processing. In the second phase, the selected relay employs the amplify-and-forward (AF) technique to forward the received signal to the IoTDs using NOMA. The information transmitted from the BS to the IoTD risks leakage by the relay, which is able to act as an eavesdropper (EAV) (i.e., an untrusted relay). To analyze the secrecy performance, we investigate three schemes: random-BS-best-relay (RBBR), best-BS-random-relay (BBRR), and best-BS-best-relay (BBBR). The physical layer secrecy (PLS) performance is characterized by deriving closed-form expressions of secrecy outage probability (SOP) for the IoTDs. A BS transmit power optimization algorithm is also proposed to achieve the best secrecy performance. Based on this, we then evaluate the system performance of the considered system, i.e., the outage probability and throughput. In addition, the impacts of the EH time, the power-splitting ratio, the numbers of BS antennas, and the numbers of untrusted relays on the SOP and throughput are investigated. The Monte Carlo approach is applied to verify our analytical results. Finally, the numerical examples indicate that the system performance of BBBR is greater than that of RBBR and BBRR.

In this paper, we investigate the system performance of multihop energy harvesting (EH) wireless sensor networks (WSNs) with imperfect channel state information (CSI) using cooperative non-orthogonal multiple access (NOMA) and friendly jammers in the presence of multiple passive eavesdroppers (EAVs). Specifically, we propose a two-phase communication protocol consisting of EH and information transmission (IT). In the first phase, relays in all clusters harvest energy from power transfer station (PTS) signals. In the first time slot of the second phase, the gateway simultaneously broadcasts information and interference signals. In the subsequent time slots, a relay acting as a friendly jammer in each cluster uses the harvested energy to send an interference signal. Simultaneously, another EH relay applies the NOMA technique to transmit the information signal according to an optimal scheduling scheme based on the maximum signal-to-interference-plus-noise ratio (SINR) of a far user (MSm) and a near user (MSn). To ensure security performance, we propose an algorithm for determining the EH time constraint for a friendly jammer. Additionally, closed-form expressions for the outage probability and throughput of the considered system are derived. Accordingly, an optimal power allocation coefficient algorithm is proposed to achieve throughput fairness for pairs of users. The results of the mathematical analysis are verified by Monte Carlo simulations. Finally, the numerical results demonstrate that the MSn scheme is recommended for guaranteeing throughput fairness for pairs of users. 

This paper investigates the problem of secure and reliable communications for cognitive radio networks. More specifically, we consider a single input multiple output cognitive model where the secondary user (SU) faces an eavesdropping attack while being subject to the normal interference constraint imposed by the primary user (PU). Thus, the SU must have a suitable power allocation policy which does not only satisfy the constraints of the PU but also the security constraints such that it obtains a reasonable performance for the SU, without exposing information to the eavesdropper. We derive four power allocation policies for different scenarios corresponding to whether or not the channel state information of the PU and the eavesdropper are available at the SU. Further, we introduce the concept secure and reliable communication probability (SRCP) as a performance metric to evaluate the considered system, as well as the efficiency of the four power allocation policies. Finally, we present numerical examples to illustrate the power allocation polices, and the impact of these policies on the SRCP of the SU. 

Recently, communication using unmanned aerial vehicles (UAVs) as relay nodes has been considered beneficial for a number of applications. Moreover, non-orthogonal multiple access (NOMA) with users being assigned different signal power levels while sharing the same time-frequency domain has been found effective to enhance spectrum utilization and provide predictable access to the channel. Thus, in this paper we consider an UAV communication system with NOMA and propose a solution to find the optimal values for the user’s power allocation coefficients (PACs) needed to achieve the required levels of communication reliability. We present a closed-form expression for the PAC of each user and also propose an algorithm for finding the optimal altitude of the UAV required to satisfy the fairness condition for all users. Finally, we provide numerical examples and compare the results for three types of communication environments.

In this paper, we study the problem of how to provide reliable communications for energy harvesting (EH) wireless sensor network (WSN). Using the example of an autonomous quarry, where self-driving trucks autonomously collect and transport goods, there is a need for multiple wireless sensors collecting data about where and when goods can be collected, while guaranteeing reliable operation of the quarry. The vehicles transfer energy to the wireless sensors within range, forming a cluster. The sensors use this energy to transmit data to the vehicles. Finally, the vehicles relay information to an access point (AP). The AP processes the collected information and synchronize the operation of all vehicles. We propose an interference channel selection policy for the sensors-to-vehicles links and vehicles-to-AP links to improve the reliability of the communications, while enhancing the energy utilization. Accordingly, closed-form expression on how to achieve reliable communication within the considered system is derived and numerical results show that the proposed channel selection strategy not only improves the probability of achieving sufficiently reliable communication but also enhances the energy utilization.