This paper proposes a dynamic gain-adaptive scheme for simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR-RIS) based non-orthogonal multiple access (NOMA) networks (termed as ASRN) with a transmit antenna selection technique at the base station to serve two vehicular users. Unlike conventional fixed-ranking NOMA, ASRN dynamically allocates power and assigns successive interference cancellation order to users based on their channel conditions. Firstly, we derive closed-form expressions for the system outage probability, asymptotic outage behavior, and diversity order, revealing that the proposed scheme achieves a diversity gain scaling with the number of STAR-RIS elements. Then, a greedy algorithm is further proposed to jointly optimize antenna selection and NOMA users' pairing. Secondly, we introduce a key performance metric (termed as the ergodic sum rate (ESR)) and define the multiple averaging ergodic sum rate (MA-ESR) to evaluate the effectiveness of ASRN scheme in delay-tolerant networking approach, when compared to other schemes. Monte Carlo simulations demonstrate that ASRN significantly outperforms dynamic gain-adaptive STAR-RIS OMA conventional STAR-RIS NOMA/OMA, and decode-and-forward relaying schemes, offering superior outage performance, coding gains, ESR performance and MA-ESR performance, particularly in vehicular environments.

ABSTRACT User selection significantly influences the efficiency and reliability of cooperative non-orthogonal multiple access (CNOMA) systems, particularly when nodes operate under radio frequency energy harvesting (RFEH). This study investigates RFEH-enabled CNOMA networks, with and without simultaneous wireless information and power transfer (SWIPT), to assess the impact of various user selection strategies under energy constraints. The system comprises a base station (BS), multiple near users, and one far user, where near users harvest energy via SWIPT and assist the far user using amplify-and-forward (AF), decode-and-forward (DF), or hybrid AF/DF relaying. The BS transmits a superimposed signal, and the selected near user performs successive interference cancellation to decode its data and forward the far user ‘s information using harvested energy. System performance over Nakagami- m fading channels is analysed in terms of outage probability, throughput, and energy efficiency, with MATLAB simulations identifying the optimal relaying and user selection combination for energy-constrained SWIPT-assisted CNOMA systems.

Indoor visible light communication (VLC) has attracted increasing attention as a promising wireless access technology because of its large unlicensed bandwidth and dual functionality of illumination and data transmission. However, practical VLC systems are vulnerable to line-of-sight (LoS) blockage caused by user mobility, human shadowing, and indoor obstacles, which may degrade link reliability and service continuity. Although hybrid VLC/RF networks can improve robustness by using RF transmission as a backup link, excessive RF fallback under severe optical blockage may overload the bandwidth-limited RF interface and reduce the service quality of RF-associated users. To address this issue, this paper investigates a risk-aware illumination-constrained resource allocation scheme for hybrid VLC/RF indoor networks under random optical blockage. A unified system model is developed by considering Lambertian optical propagation, random optical blockage, RF backup transmission, and working-plane illumination constraints. Based on this model, a joint user association and power allocation problem is formulated under QoS, transmit-power, and illumination requirements. The proposed scheme evaluates VLC service utility under blockage uncertainty, controls RF fallback to avoid excessive backup-link loading, allocates VLC/RF transmission power, and performs illumination feasibility adjustment to preserve the required lighting level. Simulation results show that, under severe blockage conditions, the proposed scheme reduces the outage probability to approximately 0.26, compared with 0.68 for VLC-only transmission and 0.47 for threshold-based VLC/RF switching. For a 20-user network, the proposed scheme achieves an average sum rate of approximately 277 Mbps, maintains a 100% illumination compliance ratio, and achieves higher energy efficiency than the benchmark schemes. Further RF backup analysis shows that the proposed scheme can maintain the service quality of RF-associated users by avoiding excessive RF fallback. These results demonstrate the effectiveness of the proposed framework for reliable and illumination-feasible hybrid VLC/RF indoor communication.

This paper investigates the propagation characteristics and system performance of terahertz–optical hybrid communication channels. To meet the increasing demand for high capacity and high reliability in future high-speed wireless communication systems, a hybrid communication model consisting of a terahertz link and an optical wireless link is established. First, the dominant propagation impairments are analyzed, including free-space path loss, molecular absorption, and pointing errors in the terahertz link, as well as atmospheric attenuation, turbulence effects, and pointing errors in the optical wireless link. Then, a hybrid channel model is developed based on an instantaneous signal-to-noise-ratio-based link selection mechanism, and outage probability, bit error rate, and channel capacity are selected as the main performance metrics. Numerical results show that the terahertz and optical wireless links exhibit clear complementarity in terms of propagation impairments. Compared with single-link transmission, the terahertz–optical hybrid communication system can effectively reduce the outage probability and maintain more stable system capacity under different transmission distances and propagation conditions. The results of this work may provide useful guidance for the design of future 6G high-speed wireless backhaul and reliable communication systems in complex environments.

The upcoming 6G networks require digital signal processing (DSP) systems which need to adapt their operations for unanticipated changes in communication channel conditions and system environmental factors because the demand for high-speed communication demands both quick response times and dependable service. The fixed processing chains of traditional DSP systems which engineers built for 5G networks together with their requirement for specific hardware usage create limits that prevent effective operation under changing environmental conditions. The paper presents ADaPT-6 (Adaptive DSP for Progressive Transceivers in 6G) as a solution to these obstacles through its entire software-based AI-powered digital signal processing system which enables real-time transceiver operation changes through intelligent learning. The ADaPT-6 system operates through two fundamental components which use FlexiTune Modulation Adaptation to enable systems to select their best modulation methods based on current channel conditions while the Signal State Evolution Engine predicts system behavior to modify system operations of filtering and equalization and synchronization. The framework achieves better spectral efficiency through its implementation of adaptive modulation together with its ability to predict signal states which improves system reliability and operational efficiency. The research shows through extensive testing in practical 6G fronthauling situations that both traditional fixed DSP systems and DSP systems with limited adaptation capabilities face performance difficulties across multiple performance metrics including bit error rate and statistical reliability and throughput and energy efficiency and latency and outage probability. The evaluation process used SNR values ranging from 0 to 20dB while measuring EVM in percentage terms and ACLR in decibels and average throughput in Mbps and latency in milliseconds and energy efficiency in bits per Joule. Quantitative evaluation demonstrates that ADaPT-6 achieves significant performance improvements over conventional DSP frameworks, including a ~ 20.8% increase in throughput (57.37Mbps vs. 47.47 Mbps), ~ 23.7% reduction in latency (20.52ms vs. 26.88ms), and ~ 44.5% improvement in energy efficiency (0.678 vs. 0.469 bits/Joule). Additionally, the framework consistently achieves lower BER and EVM across the entire SNR range (0-20dB), confirming its robustness under dynamic channel conditions. The results confirm that ADaPT-6 operates as an effective digital signal processing solution which works on any hardware platform and can be implemented at any scale. The system functions as the best solution for future AI-native 6G transceiver systems.

This paper investigates secure and low-latency communications in UAV-mounted simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR-RIS)-assisted urban vehicular networks, where severe blockage, high vehicle mobility, eavesdropping threats, and delay-sensitive traffic services coexist. In the considered system, the UAV is used not only as an aerial carrier for the STAR-RIS but also as a mobile intelligent control node that can dynamically adjust its horizontal aerial position according to vehicle distribution, blockage conditions, and eavesdropping threats. First, a UAV-STAR-RIS-assisted vehicular communication system model is developed by jointly considering urban blockage, vehicle mobility, passive eavesdropping attacks, queueing dynamics, and UAV flight constraints. Then, a high-dimensional, non-convex, and strongly coupled dynamic optimization problem is formulated to maximize the long-term average secure and low-latency utility through the joint optimization of the UAV trajectory, the STAR-RIS transmission–reflection partition ratio, the phase-shift matrices, and the transmit power allocation. Furthermore, the problem is modeled as a Markov decision process with continuous state and action spaces, and a hierarchical constrained soft actor–critic (HC-SAC)-based joint control algorithm is proposed to enable adaptive UAV movement, STAR-RIS configuration, and power control in complex dynamic environments. Simulation results demonstrate that the proposed method outperforms DDPG and several structural benchmark schemes. In the representative evaluation, the proposed HC-SAC achieves an average delay of 10.85 slots and a secrecy outage probability of 0.7160, compared with 11.72 slots and 0.8501 for PPO, and 11.94 slots and 0.8599 for DDPG. Although PPO provides the highest average secrecy rate and successful service ratio, the proposed method still maintains a competitive secure communication capability and service reliability. A normalized composite utility analysis further shows that HC-SAC attains the highest utility value of 0.9254, indicating a more favorable security–latency trade-off in complex urban vehicular scenarios.

Hurricane-related outages affect millions, yet who loses power, how severely, and for how long remains poorly measured. Here we use satellite nighttime radiance to measure outage burden across 30 Atlantic hurricanes (2012–2024) and 156,032 tract-hurricane observations in 18 states. Decomposing outage burden into occurrence, severity and recovery, we find that occurrence disparities were the most robust: minority-status vulnerability was associated with 3.47 percentage points higher outage probability per 10-percentile-point increase. Severity disparities were positive and stronger among tracts that lost power, but attenuated after land-cover adjustment, indicating dependence on built-environment characteristics. Housing and transportation vulnerability was associated with slower recovery. Outages co-occurred with dangerous heat more often in high-minority tracts. Satellite monitoring can provide a utility-independent framework for tracking whether grid resilience investments reduce outage disparities.

Hybrid integration of Low Earth Orbit (LEO) satellite systems with terrestrial networks is a critical facilitator for beyond-5G connectivity, especially in situations where terrestrial coverage is constrained by cost or feasibility. At Ka-band frequencies, link performance is extremely susceptible to propagation impairments, including rain attenuation and atmospheric absorption, as well as terrestrial interference resulting from coexistence with ground-based networks. This study offers a simulation-driven, system-level analysis of hybrid LEO-terrestrial downlink performance. A Monte Carlo framework integrates established propagation models, free-space path loss, ITU-R P.676 atmospheric absorption, ITU-R P.838 rain attenuation, and Rician small-scale fading with a distance-dependent, spatially distributed terrestrial interference formulation. The emphasis is on identifying performance regimes and reliability limitations resulting from the cumulative effects of environmental and interference factors, rather than suggesting new channel models. The study measures received power, SNR, SINR, outage probability, bit error rate, and spectral efficiency at different satellite altitudes, carrier frequencies, rainfall intensities, and levels of interference. The results show that the satellite signal weakens with increasing slant distance, causing a transition from noise-limited to interference-limited operation, and demonstrate how rain attenuation degrades Ka-band link reliability. This work further illustrates that sustaining link reliability under adverse conditions requires adaptive adjustment of performance thresholds. The simulated SNR and capacity values for clear-sky conditions are verified against published Ka-band link budget benchmarks and ITU technical data. The results offer system-level perspectives for the design and planning of hybrid satellite-terrestrial communication systems.

Differential chaos shift keying (DCSK) is a non-coherent modulation technique that has attracted attention for communication over fading channels. This paper investigates the performance of a cooperative DCSK system employing decode-and-forward (DF) relaying over Rayleigh and Nakagami-m fading environments. Analytical expressions are developed for outage probability and average-capacity evaluation, while the bit error performance is examined through an analytical treatment supported by Monte Carlo simulation. The analysis shows that the Nakagami-m fading parameter has a clear impact on system performance, where less severe fading leads to improved reliability. The results also indicate that the relay-destination link plays an important role in the cooperative gain achieved by the considered system. The contribution of the paper is presented within the scope of the adopted two-user DF cooperative DCSK model and the corresponding analytical assumptions. Therefore, the reported findings should be interpreted as an analytical and numerical characterization of the studied framework under the specified channel conditions.

This paper proposes a radio frequency (RF)/free space optics (FSO) communications hybrid system that will improve security and reliability of future sixth generation (6G) wireless communication network links with practical channel conditions. The system uses the composite Weibull-Lognormal (WLN) turbulence model for modeling the free-space-optics (FSO) link and incorporates the effects of both local fade events and global weather phenomena; it also uses Nakagami-m/Rayleigh fading to model the RF link. A hybrid link selection algorithm (HLA) is used to select the best available transmission link as a function of real-time channel characteristics. The performance of the proposed hybrid system is analyzed from three perspectives: secrecy capacity, bit-error-rate (BER), and outage probability under different fading/turbulence conditions through an exhaustive Monte-Carlo simulation process and supported by analytical results. These analyses show that this hybrid system has significant advantages over single-link systems employing either RF or FSO alone; these advantages include reduced outage probability, improved BER performance, and higher secrecy capacity especially when operating under high-turbulence conditions. These results show that a composite-fading architecture provides a reliable and secure framework for the development of fifth-generation (5G)-like communication systems which can be used in future sixth-generation (6G) wireless communication networks.

Nowadays, farmers across the globe are gradually adopting intelligent farming, which is facilitated by a variety of cutting-edge technologies. The advancement of intelligent farming applications is greatly aided by the internet of farming things (IoFT). Massive IoFT devices generally possess constrained resources, making it challenging to meet the battery and computational requirements of intelligent farming applications through local computation. RF energy harvesting enabled mobile edge computing (RFE-MEC) addresses this issue by harvesting RF energy from an access point, offloading and computing tasks at the edge in a nearby access point. In the proposed scheme, multiuser nonorthogonal multiple access allows the IoFT devices to simultaneously offload computationally intensive tasks to the MEC server for processing. The delay outage probability closed-form expression is formulated for the RFE-NOMA-MEC intelligent farming system under a Rayleigh fading channel. The impact of imperfect channel state information on the RFE-NOMA-MEC is considered. Tunicate enhanced northern goshawk optimization algorithm (TNGO) has been proposed to discover the optimal parameter set to minimize delay outage probability. The results indicate that the system performance is enhanced using TNGO when the optimal time switching factor, power allocation coefficient and task allocation ratio are utilized.

Abstract Underwater visible light communication (UVLC) has emerged as a promising solution for high-speed and low-latency underwater communication; however, its performance is fundamentally constrained by severe channel impairments and the limited energy availability of underwater sensor nodes. In this paper, an intelligent reflecting surface (IRS)-assisted UVLC framework with energy harvesting is proposed, where both spatial and temporal resources are jointly optimized to enhance system reliability and sustainability. Specifically, the IRS is adaptively partitioned into two groups to simultaneously support energy harvesting and data transmission, while the transmission frame is dynamically divided to determine the optimal harvesting duration. Unlike existing works that rely on static IRS allocation and static harvesting time, the proposed scheme formulates a joint optimization problem to maximize the ergodic capacity under a minimum energy constraint. By using Karush-Kuhn-Tucker (KKT) conditions, closed-form expressions for the optimal harvesting time and IRS partitioning are obtained, and key insights are provided on the trade-off between energy harvested and information transfer. Furthermore, the closed-form expressions for ergodic capacity, harvested energy, and outage probability are derived using practical underwater channel conditions, such as absorption, scattering, turbulence, different link distances, etc. The simulation results are presented to demonstrate the effectiveness of the proposed framework over the conventional schemes.

ABSTRACT Satellite communication fulfills the demand of global connectivity for next‐generation networks. Free space optical (FSO) communication connects these high‐bandwidth global links for seamless transmission. High altitude platform station (HAPS) improves the outage probability by relaying the signal when transmission to the long distances in one hop is not reliable. In this work, we consider adaptive beam divergence (ABD) technique for a low earth orbit (LEO) satellite, which transmits the FSO signal to the HAPS, where the divergence angle of the signal is selected based on the altitude of the HAPS. We considered the effects of threshold signal‐to‐noise ratio (SNR), receiver aperture diameter, jitter standard deviation, optical‐to‐electrical conversion efficiency and the horizontal distance between satellite and HAPS on the link outage probability. The results show that by using an appropriate beam divergence angle according to the height of the HAPS, the performance of the system improves. Additionally, it is observed that for a fixed outage probability, ABD achieves communication for longer transmission range with the HAPS located at an altitude, which is lower in comparison with the altitudes at lower and upper fixed divergence angles by 1.610 and 2.169 km, respectively.

Outage probability analysis of triple-hop UAV-based FSO combined with hybrid RF-UWOC link for integrated aerial-to-underwater communication systems

Analysis of spatial secrecy outage probability and throughput optimization for Nakagami-m wiretap channels in IIoT

This paper investigates the internal secrecy and external covertness of a mixed-trust autonomous aerial vehicle (AAV) communication system assisted by rate-splitting multiple access (RSMA). In this setting, a semi-trusted user with partial decoding capability poses an internal eavesdropping threat, while multiple distributed wardens attempt to detect the transmission from the AAV to the semi-trusted user, creating an external covertness challenge. To characterize these security aspects, a unified analytical framework is developed. First, the internal eavesdropping capability of the semi-trusted user is quantified by deriving a closed-form expression for its eavesdropping success probability. Based on the outcome of the eavesdropping attempt, tractable expressions for the secrecy outage probability of the legitimate user are obtained. Furthermore, the external covertness performance is analyzed by deriving closed-form false alarm probability, missed detection probability, and detection error probability (DEP) for an individual warden, together with the optimal detection threshold and the corresponding minimum DEP. The cooperative global detection performance with multiple wardens is further characterized under conservative fusion rules. Extensive Monte Carlo simulations validate the analytical results and, through a joint evaluation of secrecy, reliability, and covertness metrics, illustrate the feasible operating regions enabled by RSMA power allocation in comparison with a NOMA baseline. The results provide a comprehensive theoretical basis for the design of secure and covert AAV communication strategies in mixed-trust environments.

Underwater wireless optical communication (UWOC) has emerged as a promising solution for short-range high-speed underwater data transmission in recent years. For what is believed to be the first time, this work presents a comprehensive secrecy performance analysis of a downlink non-orthogonal multiple access (NOMA)-UWOC system over the composite vertically stratified Weibull-generalized gamma (WGG) oceanic fading channel, in which the impacts of path loss, underwater turbulence, pointing errors, and angle-of-arrival fluctuations are considered. Specifically, the closed-form expressions for the probability density function (PDF) and cumulative distribution function (CDF) of the vertically stratified WGG fading channel coefficient are derived analytically. Then, on the basis of these derivations, analytical frameworks for the key secrecy performance metrics, including secrecy outage probability, strictly positive secrecy capacity, and effective secrecy throughput, are obtained, taking into account the residual interference from successive interference cancellation (SIC), which are validated through Monte Carlo simulations. Finally, the effects of the number of layers, the thermohaline gradient and air bubbles, the residual power factor of imperfect SIC, the transceiver misalignment, and the angle-of-arrival deviation are investigated on this UWOC system. The presented results give valuable insights into the practical aspects of deployment of UWOC networks.

ABSTRACT Rate‐splitting multiple access (RSMA) is a promising enabler for improving spectral efficiency, interference management, and user fairness in satellite downlink systems. Yet, most RSMA studies are either tailored to terrestrial settings or rely primarily on numerical optimization, offering limited analytical insight under satellite‐realistic propagation such as shadowing. Motivated by geostationary Earth orbit (GEO) downlink operation, this paper provides a tractable performance analysis of an RSMA‐enabled single‐beam multiuser downlink over shadowed Rician fading. We consider a ‐antenna GEO satellite serving single‐antenna users with maximum‐ratio transmission (MRT)–based precoding and perfect successive interference cancellation (SIC). Closed‐form expressions are derived for the distribution of the effective channel gain, leading to exact and high‐SNR outage probability characterizations. The resulting formulas explicitly reveal the roles of the antenna count (defined as the number of satellite transmit antennas ), shadowed Rician parameters, and RSMA power allocation. Furthermore, the analysis yields simple feasibility conditions that delineate practical operating regions for common/private power splitting. We obtain user and system throughput expressions and identify that the achieved diversity order equals . Monte Carlo simulations validate the analysis and benchmark RSMA against nonorthogonal multiple access (NOMA) under various shadowing levels and power‐allocation settings, highlighting reliability–rate trade‐offs and providing actionable guidance for GEO satellite downlink design.

This paper investigates an intelligent reflecting surface (IRS)-assisted hybrid high-altitude platform (HAP) and unmanned aerial vehicle (UAV) uplink communication network employing non-orthogonal multiple access (NOMA). A unified uplink system model is developed that jointly captures UAV three-dimensional deployment, IRS-assisted composite channels, SIC-based uplink NOMA reception, and shared-spectrum cross-tier interference between HAP and UAV layers. To efficiently support dense uplink connectivity, a joint uplink sum-rate maximization problem is formulated under practical mobility, power, quality-of-service, and interference constraints, resulting in a highly non-convex mixed-integer optimization problem. A low-complexity block coordinate descent (BCD)-based framework is proposed to iteratively optimize UAV deployment, user association, uplink power allocation, and IRS phase shifts. The proposed framework is particularly well-suited for high-capacity data offloading and IoT-based safety monitoring in remote mining environments, supporting the digital transformation of the mining sector in alignment with Saudi Vision 2030. Extensive simulations demonstrate that the proposed framework significantly outperforms conventional aerial and terrestrial benchmarks. Specifically, compared to hybrid HAP–UAV uplink NOMA without IRS, the proposed design improves the uplink sum rate by up to 23.03% and by an average of 15.39% over K=10–100 simultaneously scheduled users. Relative to UAV-only and HAP-only IRS-assisted uplink schemes, gains of up to 43.80% and 59.01% are achieved, respectively, while effective improvement is observed over terrestrial uplink baselines under dense user loading. Moreover, IRS-assisted user association yields additional gains of up to 21.45% in sum rate, while outage probability is substantially reduced across the entire SINR range. These results confirm that IRS-assisted hybrid HAP–UAV uplink NOMA provides a scalable and reliable solution for future 6G-oriented dense uplink communication networks.

To meet the future demands of high-rate transmission and full-coverage networks, radio frequency-underwater wireless optical communication (RF-UWOC) relaying systems are considered a promising heterogeneous communication architecture. The rate-splitting (RS) scheme, through its power allocation (PA) mechanism, provides a generalized framework for the performance evaluation of such systems. Based on this, this paper analyzes the performance of an RS-based RF-UWOC system under hardware impairments (HIs) and interference. Analytical expressions of the outage probability (OP) and ergodic capacity (EC) for the considered system are formulated within a generalized framework, which encompasses the conventional RF-UWOC system as a special case. The results indicate that the OP and EC are affected by HIs, interference transmit power, the PA coefficients, channel fading, pointing errors (PEs), and detection types of the UWOC link. Furthermore, the asymptotic results for the OP and the diversity gain (DG) are explicitly characterized. For a fixed interference transmit power, the DG is mainly dominated by the channel fading severity, PEs effect, and the detection scheme. When the interference transmit power is comparable to the desired signal power, the system operates in an interference-limited regime, and the DG decreases to zero. It is also revealed that HIs and PA coefficients affect the coding gain but not the DG. Moreover, the existence of an optimal PA scheme improves the reliability of the RS-based system.