Underwater exploration, inspection, and surveillance have become more popular thanks to recent advancements in underwater wireless communication technologies, of which underwater wireless optical communication (UWOC) boasts increased bandwidth, reduced latency, and heightened security. Normally, once underwater sensors collect the data, it is transmitted to remote offices through a relay node stationed on the sea surface. In this study, our focus is on establishing and analyzing the performance of secrecy outage in an uplink hybrid radio frequency (RF)-UWOC space-ocean system that comprises a collection of underwater sensors, a relay floating on the ocean surface, a legitimate satellite receiver, and an eavesdropping satellite. In the considered system, the transmission performance from end-to-end is influenced by several factors. These include path loss, small-scale fading, position randomness of the satellites in RF links, propagation loss, turbulence-induced fading, and random location distribution of the underwater sensors in UWOC links. To enhance our understanding of system design, geometric probability theory is employed to investigate the end-to-end secrecy outage performance of the dual-hop RF-UWOC space-ocean uplink transmission while comprehensively considering the impacts of these factors. Finally, the accuracy of the proposed analysis models is verified through numerical results.

This letter investigates the secure delivery performance of the rate-splitting multiple access scheme in land mobile satellite (LMS) systems, considering that the private messages intended by a terminal can be eavesdropped by any others from the broadcast signals. Specifically, the considered system has an N -antenna satellite and numerous single-antenna land users. Maximum ratio transmission (MRT) and matched-filtering (MF) precoding techniques are adopted at the satellite separately for the common messages (CMs) and for the private messages (PMs), which are both implemented based on the estimated LMS channels suffering from the Shadowed-Rician fading. Then, closed-form expressions are derived for the ergodic rates for decoding the CM, and for decoding the PM at the intended user respectively, and more importantly, we also derive the ergodic secrecy rate against eavesdropping. Finally, numerical results are provided to validate the correctness of the proposed analysis models, as well as to show some interesting comparisons.

With the rapidly increasing demands for wireless communication networks, unmanned aerial vehicles (UAVs) have been developed. However, the line-of-sight (LoS) links are susceptible to severe deterioration due to complex distribution environments. To tackle this issue, Reconfigurable Intelligent Surface (RIS) technology has been introduced to ameliorate the propagation environment and enhance communication performance. This paper explores a RIS-assisted simultaneous wireless information and power transfer (SWIPT) system to investigate the optimization problem involving UAV trajectory design, precoding, and RIS phase shift. The objective is to maximize the minimum information receivers' (IRs) rate. Considering that the problem is nonconvex, we decompose it into three subproblems and then solve it using an alternating optimization algorithm and the successive convex approximation (SCA) technique. Additionally, the paper takes into account the phase dispersion of the UAV no-fly zone and RIS, based on the actual situation. To address these non-ideal factors, we introduce an indicator function flag and employ the Dinkelbach method to obtain the optimal solution for the non-ideal optimization problem. The numerical results demonstrate that the proposed algorithm considerably improves the rate performance of the system.

Low Earth Orbit (LEO) satellite systems with sensing capabilities are widely regarded as promoting reliable and efficient communication services globally. This paper proposes a Multi-Satellite Collaborative Security System with Integrated Sensing and Communication (ISAC-MSC). Considering the potential benefits of LEO satellites and ISAC, we exploit sensing performance in the MSC system by jointly optimizing LEO satellite assignments, communication Beamforming (BF) vectors, and sensing BF vectors. Specifically, we design improved Continuous Particle Swarm (CP) optimization and Discrete Particle Swarm (DP) optimization algorithms to maximize the target sensing Signal-to-Noise Ratio (SNR) for LEO satellite assignments. Additionally, with respect to the BF vector optimization, we develop Power Approximation (PA) optimization algorithm, Inner Approximation (IA) optimization algorithm, and Joint Sensing and Communication BF (JSC-BF) optimization algorithm. Multiple algorithms are tightly integrated and alternately iterated. Numerical results show that: 1) the JSC-BF algorithms outperform the PA and IA algorithms in terms of sensing performance and communication secrecy rate; 2) compared to the single satellite case, the ISAC-MSC system performance approximately linear growth, and has strong extensibility; 3) with imperfect MSC synchronization case, the communication secrecy rate appears inflection point and stabilization, but the JSC-BF algorithms still have excellent performance.

With the development of satellite communication technology, the application of satellites in the Internet of Vehicles (IoV) system can effectively solve the limitations and deficiencies of ground communication networks. In this paper, we investigate the security outage performance of a satellite-vehicle communication system consisting of a satellite ( $S$ ), a legitimate receiving vehicle ( $C$ ), and an eavesdropping vehicle ( $E$ ), where $C$ and $E$ are randomly located on two different roads within the coverage area of $S$ and randomly distributed on their respective roads. The downlink communication links between $S$ and these terrestrial vehicles are assumed to suffer the Shadowed-Rician fading. Then, the security outage probability (SOP) is studied under the most straightforward case that $ C$ and $E$ are equipped with a single antenna. Next, we extend to the more common scenario where both $C$ and $E$ adopt multiple antennas by deriving the analytical expression for the SOP. Finally, numerical results are presented to verify our proposed analytical models.

Space-air-ground integration has become paramount in the next generation of wireless communication systems in the era marked by the seamless integration of terrestrial and celestial domains. On the other hand, the age of information (AoI) has recently emerged as a vital metric for evaluating the timeliness and freshness of data in these multi-hop communication systems. This paper focuses on investigating the information freshness of multi-hop satellite IoT systems while considering several automatic repeat request (ARQ) and hybrid ARQ (HARQ) schemes over different hops to promise the reliability of data transmissions. Specifically, a group of remote sensors transmits their data to a terrestrial base station (B) via the code-division multiple access (CDMA) strategy to exploit CDMA’s natural merits, e.g., anti-jamming and simultaneous transmissions. Then, B sends these received data to a data destination (D) via a satellite (R) under the transparent forwarding strategy. We derive the closed form of the outage probability for the CDMA protocol considering multi-user interference (MUI) and the closed form of the end-to-end outage probability for the three kinds of ARQ and HARQ schemes on the dual-hop B-R-D transmission, and then finally derive the expression of the corresponding AoI. Finally, numerical results show that simulations match well with the theoretical results, proving the analysis’s correctness and the pros and cons of the different ARQ/HARQ schemes.