This paper introduces the concept of wireless-powered zero-energy reconfigurable intelligent surface (zeRIS), and investigates a wireless-powered zeRIS aided communication system in terms of security, reliability and energy efficiency. In particular, we propose three new wireless-powered zeRIS modes: 1) in mode-I,Nreconfigurable reflecting elements are adjusted to the optimal phase shift design of information user to maximize the reliability of the system; 2) in mode-II,Nreconfigurable reflecting elements are adjusted to the optimal phase shift design of cooperative jamming user to maximize the security of the system; 3) in mode-III,N1andN2(N1+N2=N) reconfigurable reflecting elements are respectively adjusted to the optimal phase shift designs of information user and cooperative jamming user to balance the reliability and security of the system. Then, we propose three new metrics, i.e., joint outage probability (JOP), joint intercept probability (JIP), and secrecy energy efficiency (SEE), and analyze their closed-form expressions in three modes, respectively. The results show that under high transmission power, all the diversity gains of three modes are 1. Among three modes, mode-I achieves the best JOP, while mode-II achieves the best JIP. We exploit two security-reliability trade-off (SRT) metrics, i.e., JOP versus JIP, and normalized joint intercept and outage probability (JIOP), to reveal the SRT performance of the proposed three modes. Interestingly, mode-III achieves the lowest normalized JIOP with increasing time allocation factor, and the highest SEE with increasing transmission power. However, mode-I has the highest SEE with increasing predefined data rate. The optimal zeRIS deployment for mode-I and mode-III is near the PS, while that for mode-II is near the AP.

This article investigates the simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR-RIS) assisted secure transmissions in wireless powered communication (WPC) systems. According to the conditions of communication links, three scenarios are considered. Correspondingly, two transmission schemes are proposed for outdoor and indoor users to enhance the reliability and security of the communication system in each scenario. To be specific, for the scenario-I with blocked energy harvesting links, the scenario-I based information transmission of outdoor-user and cooperative jamming of indoor-user (IbTOJI) scheme, and cooperative jamming of outdoor-user and information transmission of indoor-user (IbJOTI) scheme are proposed, respectively. For the scenario-II with blocked information transmission (IT) links, scenario-II-based IT of outdoor-user and cooperative jamming of indoor-user (IIbTOJI) scheme, and cooperative jamming of outdoor-user and IT of indoor-user (IIbJOTI) scheme are proposed, respectively. For the scenario-III which deploys a hybrid access point (HAP), the direct links of the energy harvesting and IT are blocked. Scenario-III-based IT of outdoor-user and cooperative jamming of indoor-user (IIIbTOJI) scheme, and cooperative jamming of outdoor-user and IT of indoor-user (IIIbJOTI) scheme are proposed, respectively. We analyze the closed-form expressions of outage probability and intercept probability for each scheme. The result shows that IIIbTOJI scheme has the best reliable performance among the proposed schemes, and IbJOTI and IIIbJOTI schemes perform best in security.

This paper investigates a novel anti-eavesdropping strategy based on unmanned aerial vehicle (UAV)-mounted simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR-RIS). In particular, a UAV equipped with a STAR-RIS acts as a passive relay to reflect desired signals and simultaneously acts as a friendly jammer to transmit artificial noise (AN) against eavesdroppers. Based on the phase shift coupling characteristics of STAR-RIS, three phase shift configuration strategies are proposed, namely reliability-priority (RP), security-priority (SP), and element-partitioning (EP) schemes. Analytical closed-form expressions of connection outage probability (COP), secrecy outage probability (SOP), effective secrecy throughput (EST) and secrecy energy efficiency (SEE) are derived to evaluate the reliable and secure performance achieved by the proposed schemes, respectively. The asymptotic analysis is also performed for further insights. Analysis and simulation results demonstrate that the proposed three schemes outperform traditional benchmark schemes. From the perspective of reliability, the RP scheme can achieve the best COP. In terms of security, as the number of STAR-RIS elements increases, the SOPs of the SP and EP exponentially decrease, whereas the SOP of the RP scheme increases. The EP scheme achieves the optimal EST, and the asymptotic EST is independent of phase estimation errors. Additionally, it is recommended that the UAV be deployed near the eavesdropper for the SP and EP schemes to enhance SEE.

This paper investigates the physical layer security for a double-reconfigurable intelligent surface (DRIS) aided wireless-powered communication (WPC) system in the presence of an eavesdropper, where one RIS (termed as RIS-1) is deployed between power station (PS) and information user (U) while the other RIS (termed as RIS-2) is deployed between U and access point (AP). Moreover, an idle user acts as a cooperative jamming user (J) to emit the artificial noise to improve the transmission security of U. According to different types in energy harvesting (EH) and information transmission (IT)/noise transmission (NT) of U/J, we propose four DRIS enabled wireless-powered cooperative jamming transmission schemes based on jointly enhancing EH and IT of U (namely DRIS-1), jointly enhancing EH of U and NT of J (namely DRIS-2), jointly enhancing EH of J and IT of U (namely DRIS-3), and jointly enhancing EH and NT of J (namely DRIS-4), respectively. We analyze connection outage probability (COP), secrecy outage probability (SOP), and effective secrecy throughput (EST) of the proposed four schemes, respectively. The results show that DRIS-1 scheme has the highest diversity gain among the four schemes. Besides, the gain of the number of reflecting elements at RIS-1 has the same order as that at RIS-2 in DRIS-1 scheme and DRIS-4 scheme. In DRIS-2 scheme, the gains of the number of reflecting elements at RIS-1 and RIS-2 are two powers and one power, respectively, while the opposite is true in DRIS-3 scheme. In addition, DRIS-1 scheme achieves the best COP, while DRIS-4 scheme achieves the best SOP. DRIS-1 scheme, DRIS-3 scheme, and DRIS-4 scheme respectively achieve the best EST in the low, middle, and high region of transmission power or number of RIS elements.

This paper studies the physical layer security for a double reconfigurable intelligent surface (RIS) aided wireless powered communication system in the presence of an eaves-dropper, where a user acts as friendly jammer (J) to emit the artificial noise to improve the transmission security of another user. In particular, three RIS transmission schemes are proposed: 1) In scheme-I, both RISs are designed as optimal phase shift of wireless user (U); 2) In scheme-II, the first RIS is designed as optimal phase shift of U and the second RIS is designed as optimal phase shift of J, respectively; 3) In scheme-III, the first RIS is designed as optimal phase shift of J and the second RIS is designed as optimal phase shift of U, respectively. To reveal the achieved reliability and security performance of proposed three schemes, we analyze the connection outage probability (COP) and secrecy outage probability (SOP), respectively. The results show that scheme-II and scheme-III have the same COP performance and both of them are worse than scheme-I. The scheme-III achieves the best SOP performance, while scheme-I achieves the worst SOP performance that is slightly inferior to scheme-II.

This paper studies simultaneous transmitting and reflecting reconfigurable intelligent surface (STAR-RIS) aided secure wireless powered communication. Specifically, we propose an energy splitting protocol based STAR-RIS transmission scheme, combined with an uplink non-orthogonal multiple access (NOMA), to enhance both energy transfer and information transmission for indoor and outdoor users against eavesdropping attacks. The accurate and asymptotic connection outage probabil-ities, secrecy outage probability, and effective secrecy throughput are analyzed to evaluate the proposed scheme's performance and the impact of key parameters. Simulation results indicate that the proposed scheme significantly outperforms the dual transmit/reflect-only RIS scheme. Although slightly less effective than traditional direct transmission scheme at the low transmit power region, the proposed scheme's efficacy rapidly surpasses that of direct transmission as the transmit power increases.

Reconfigurable intelligent surface (RIS) is viewed as a promising technique that can be utilized to improve the performance of systems by reconfiguring signal propagation environments. This article investigates green and secure unmanned aerial vehicle (UAV) Internet of Things (IoT) communications with the aid of RIS, where multiple UAVs harvest energy from a power beacon (PB) and send information uplink to access point (AP) with nonorthogonal multiple access (NOMA). In particular, communication can be divided into two phases during each time frame: 1) energy transfer and 2) information transmission (IT). Three RIS deployment strategies are proposed. In mode I, RISs are deployed between UAVs and AP to enhance the IT. In mode II, RISs are deployed between PB and UAVs to enhance the energy transfer. In mode III, RISs are deployed between UAVs and a hybrid AP (HAP) to enhance energy transfer and IT simultaneously. Considering phase compensation error caused by imperfect conditions, we define and evaluate ergodic capacity (EC), EC probability (ECP) and ergodic secrecy capacity (ESC) of three modes to measure the reliability and security of the system. The asymptotic expressions are also derived for further insights. Numerical results are presented to validate the correctness of theoretical derivations. Results demonstrate that the passive beamforming gain promised by RIS can significantly enhance the performance of systems. Mode III outperforms other modes in terms of reliability and security. When the transmission power and the number of UAVs increase, the ESCs of modes I and III converge to the same performance floor.

This article investigates a reliable and secure wireless-powered communication system assisted by a simultaneous transmitting and reflecting reconfigurable intelligent surface (STAR-RIS) serving indoor and outdoor users. To align with practical application, we consider two eavesdropping conditions: mixed and indirect eavesdropping links. To improve the reliability and security of downlink energy transfer (ET) and uplink information transmission (IT), we propose four STAR-RIS schemes utilizing time-switching (TS) and energy-splitting (ES) protocols: 1) The dual-TS (DTS) scheme employs the TS protocol for both downlink ET and uplink IT; 2) The mixed ES-TS (MET) scheme switches from the ES protocol in downlink ET to the TS protocol in uplink IT; 3) The dual-ES (DES) scheme employs the ES protocol for both downlink ET and uplink IT; 4) The mixed TS-ES (MTE) scheme switches from the TS protocol in downlink ET to the ES protocol in uplink IT. Further, accurate and asymptotic connection outage probability, secrecy outage probability, and effective secrecy throughput are analyzed for each proposed scheme. Theoretical analysis and simulation results demonstrate that: 1) At high transmission power or with a large number of STAR-RIS elements, the MTE scheme achieves the highest reliability. Conversely, the DES scheme provides the best reliability at lower transmission power or with fewer STAR-RIS elements; 2) Under indirect eavesdropping links, the DES scheme achieves the highest security, followed by the MTE, MET, and DTS schemes. However, this performance order is reversed under mixed eavesdropping links; 3) The DES scheme achieves the best overall performance, followed by the MTE, MET, and DTS schemes, all of which outperform the benchmark schemes.