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.INDEX TERMS Energy harvesting, Internet of Things, physical layer secrecy, throughput, NOMA, MISO, untrusted relay.

The next generation power grid (the "Smart Grid") aims to minimize environmental impact, enhance markets, improve reliability and service, and reduce costs and improve efficiency of electricity distribution. One of the main protocol frameworks used in Smart Grids is IEC 61850. Together with the Manufacturing Message Specification (MMS) protocol, IEC 61850 ensures interoperability within the Smart Grid by standardizing the data models and services to support Smart Grid communications, most notably, smart metering and remote control. Long Term Evolution (LTE) is a fourth-generation (4G) cellular communications standard that provides high-capacity, low-latency, secure and reliable data-packet switching. This paper investigates whether LTE can be used in combination with IEC 61850 and MMS to support smart metering and remote control communications at a desirable quality of service level. Using ns-3 simulation models, it is shown that LTE can indeed satisfy the main IEC 61850 and MMS performance requirements for these two applications.

This paper investigates system performance in the Internet of Things (IoT) with an energy harvesting (EH) unmanned aerial vehicle (UAV)-enabled relay under Nakagami-m fading, where the time switching (TS) and adaptive power splitting (APS) protocols are applied for the UAV. Our proposed system model consists of a base station (BS), two IoT device (ID) clusters (i.e., a far cluster and a near cluster), and a multiantenna UAV-enabled relay (UR). We adopt a UR-aided TS and APS (U-TSAPS) protocol, in which the UR can dynamically optimize the respective power splitting ratio (PSR) according to the channel conditions. To improve the throughput, the nonorthogonal multiple access (NOMA) technique is applied in the transmission of both hops (i.e., from the BS to the UR and from the UR to the ID clusters). The U-TSAPS protocol is divided into two phases. In the first phase, the BS transmits a signal to the UR. The UR then splits the received signal into two streams for information processing and EH using the APS scheme. In the second phase, the selected antenna of the UR forwards the received signal to the best far ID (BFID) in the far cluster and the best near ID (BNID) in the near cluster using the decode-and-forward (DF) or amplify-and-forward (AF) NOMA scheme. We derive closed-form expressions for the outage probabilities (OPs) at the BFID and BNID with the APS ratio under imperfect channel state information (ICSI) to evaluate the system performance. Based on these derivations, the throughputs of the considered system are also evaluated. Moreover, we propose an algorithm for determining the nearly optimal EH time for the system to minimize the OP. In addition, Monte Carlo simulation results are presented to confirm the accuracy of our analysis based on simulations of the system performance under various system parameters, such as the EH time, the height and position of the UR, the number of UR antennas, and the number of IDs in each cluster.

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In this paper, we investigate the physical layer security (PLS) of a wireless sensor network (WSN) that consists of a base station (BS), multiple sensor nodes (SNs), and multiple energy-limited relays (ERs) in the presence of a passive eavesdropper (EAV). We adopt a time-switching/power-splitting (TSPS) mechanism for information transmission. The communication protocol is divided into two phases. The purpose of the first phase is to decode information, and energy harvesting (EH) is performed in accordance with the TSPS protocol. The purpose of the second phase is to transmit information to multiple destinations using the amplify-and-forward (AF) technique. In this study, we introduce a multirelay cooperative scheme (MRCS) to improve the secrecy performance. We derive analytical expressions for the secrecy outage probability (SOP) of the MRCS and that of the noncooperative relay scheme (NCRS) by using the statistical characteristics of the signal-to-noise ratio (SNR). Specifically, we propose an optimal relay selection scheme to guarantee the security of the system for the MRCS. In addition, Monte Carlo simulation results are presented to confirm the accuracy of our analysis based on simulations of the secrecy performance under various system parameters, such as the positions and number of ERs, the EH time, and the EH efficiency coefficients. Finally, the simulation results show that the secrecy performance of our MRCS is higher than that of the NCRS and the traditional cooperative relay scheme (TCRS).INDEX TERMS Energy harvesting, cooperative relay, time-switching/power-splitting, physical layer security.