We investigate the secrecy transmission of uplink non-orthogonal multiple access (NOMA) with the aid of energy harvesting (EH) jammers. During each time frame, communication is divided into two phases. At the first phase, the base station (BS) transfers wireless power to EH receivers (EHRs). At the second phase, users perform uplink NOMA transmission to BS, while one of EHRs is selected as a friendly jammer that uses the energy harvested from the previous phase to emit the artificial noise for confusing the eavesdropper. In terms of the requirement of channel state information (CSI), we propose three friendly EH jammer selection schemes, namely random EH jammer selection (REJS) scheme without the requirement of any CSI, maximal EH jammer selection (MEJS) scheme with the CSI between BS and each EHR, and optimal EH jammer selection (OEJS) scheme where both the CSIs from BS to EHRs and from EHRs to the eavesdropper need to be known. Analytical closed-form expressions for the connection outage probability (COP), secrecy outage probability (SOP) and effective secrecy throughput (EST) are derived to evaluate the system performance achieved by the proposed schemes, respectively. Also, the asymptotic analysis is provided to gain further insights. The analytical and numerical results indicate that the proposed schemes can realize better secrecy performance than conventional scheme without an EH jammer. Both the secrecy diversity orders of the REJS and MEJS schemes are one while the OEJS scheme can achieve a full secrecy diversity order. Furthermore, owing to the impact of connection outage, the three schemes converge to the same EST floor with the increase of signal-to-noise ratio (SNR).

The intrinsic integration of the nonorthogonal multiple access (NOMA) and reconfigurable intelligent surface (RIS) techniques is envisioned to be a promising approach to significantly improve both the spectrum efficiency and energy efficiency for future wireless communication networks. In this paper, the physical layer security (PLS) for a RIS-aided NOMA 6G networks is investigated, in which a RIS is deployed to assist the two “dead zone” NOMA users and both internal and external eavesdropping are considered. For the scenario with only internal eavesdropping, we consider the worst case that the near-end user is untrusted and may try to intercept the information of far-end user. A joint beamforming and power allocation sub-optimal scheme is proposed to improve the system PLS. Then we extend our work to a scenario with both internal and external eavesdropping. Two sub-scenarios are considered in this scenario: one is the sub-scenario without channel state information (CSI) of eavesdroppers, and another is the sub-scenario where the eavesdroppers' CSI are available. For the both sub-scenarios, a noise beamforming scheme is introduced to be against the external eavesdroppers. An optimal power allocation scheme is proposed to further improve the system physical security for the second sub-scenario. Simulation results show the superior performance of the proposed schemes. Moreover, it has also been shown that increasing the number of reflecting elements can bring more gain in secrecy performance than that of the transmit antennas.

This article studies the reliable and secure communications for a wireless-powered non-orthogonal multiple access (NOMA) system in the presence of multiple eavesdroppers. A joint artificial noise and power allocation (JAP) scheme is proposed to ensure the reliability and security for the system. Based on the JAP scheme, analytical closed-form expressions for connection outage probability (COP), secrecy outage probability (SOP) and effective secrecy throughput (EST) are derived, respectively, to evaluate the performance of the security-required user. Also, the asymptotic SOP and EST are analyzed to gain further insights. The numerical results demonstrate the correctness of the theoretic analysis and indicate that the proposed JAP scheme can achieve a better performance than the benchmark schemes.

This letter studies physical layer security (PLS) of an intelligent reflecting surface (IRS) aided wireless powered communication (WPC) system in the presence of a passive eavesdropper, and proposes three secure IRS-WPC modes. In mode-I, the IRS is deployed between hybrid access point (HAP) and wireless user (U) for co-located power station (PS) and access point (AP). In mode-II, the IRS is deployed between AP and U for separate PS and AP, while in mode-III, the IRS is deployed between PS and U for separate PS and AP. For each mode, the optimal phase shift is designed to maximize the reception of energy and information at legitimate receiver. The accurate and asymptotic ergodic secrecy capacity (ESC) of each mode is analyzed, and various new closed-form expressions are obtained. The results reveal that mode-I and mode-II significantly outperform benchmark without IRS, while mode-III outperforms benchmark without IRS under lower transmission power or small number of IRS elements.

To enhance the spectral efficiency of non-orthogonal multiple access (NOMA) in massive multiple input multiple output (MIMO) systems, we propose a user pairing and pair scheduling (UPaS) algorithm, which can, simultaneously, pair the selected users and schedule suitable user pairs for data transmission. Through dividually selecting the first user and the second user for each user pair, the proposed algorithm can make sure that both the two users in each user pair can make the greatest contribution to the system sum rate. To suppress the inter-pair interference, we design an interference cancellation combining (ICC) matrix, which firstly breaks through the constraint between antenna numbers of base station (BS) and users. Theoretical analyses and computer simulations show that, the proposed algorithm has excellent sum rate and outage performance compared with traditional user pairing algorithms.

The miniaturization of satellite payloads and the reduction in launch costs have driven the rapid development of Low Earth Orbit (LEO) satellites in the fields of communication, navigation, and remote sensing (CNS), reshaping the industry and global information infrastructure. However, there remain significant challenges and obstacles in the application of LEO satellites within these domains. This paper aims to provide a comprehensive analysis of LEO satellites, with particular emphasis on the development and challenges of communication payloads, to promote further research and applications in these areas. First, the paper examines the evolution of LEO systems and communication payload capabilities from different historical perspectives and user demands. It then explores the opportunities for LEO satellites in the context of global communication infrastructure, particularly in enhancing global connectivity, supporting intelligent transportation through high-precision positioning, navigation, and timing (PNT), and advancing environmental monitoring via passive radar in remote sensing applications. By systematically reviewing the literature on network architectures, medium access control, physical layer technologies, constellation designs, interference management, the application of artificial intelligence, and cost control strategies, this study identifies the major challenges these technologies face in CNS applications. Additionally, the paper discusses future research directions, including large-scale constellations, multi-functional platform integration, advances in intelligence and automation, network convergence and interoperability, interference mitigation, and sustainability. These areas are explored to provide pathways for further technological advancements.