Search Results (70)

To enable accurate evaluation of satellite laser communication terminals under solar outage interference, this paper presents the design and implementation of a solar radiation simulation system targeting the 1540–1560 nm communication band. The system reconstructs co-propagating interference conditions through standardized and continuously tunable output, based on high irradiance and spectral uniformity. A compound beam homogenization structure—combining a multimode fiber and an apodizator—achieves 85.8% far-field uniformity over a 200 mm aperture. A power–spectrum co-optimization strategy is introduced for filter design, achieving a spectral matching degree of 78%. The system supports a tunable output from 2.5 to 130 mW with a 50× dynamic range and maintains power control accuracy within ±0.9%. To suppress internal background interference, a BRDF-based optical scattering model is established to trace primary and secondary stray light paths. Simulation results show that by maintaining the surface roughness of key mirrors below 2 nm and incorporating a U-shaped reflective light trap, stray light levels can be reduced to 5.13 × 10⁻¹² W, ensuring stable detection of a 10⁻¹⁰ W signal at a 10:1 signal-to-background ratio. Experimental validation confirms that the system can faithfully reproduce solar outage conditions within a ±3° field of view, achieving consistent performance in spectrum shaping, irradiance uniformity, and background suppression. The proposed platform provides a standardized and practical testbed for ground-based anti-interference assessment of optical communication terminals. Full article

Safety and performance validation of autonomous agricultural robots is critically dependent on realistic, mobile test environments that provide high-fidelity ground truth. Existing infrastructures focus on either component-level sensor evaluation in fixed setups or system-level black-box testing under constrained conditions, lacking true mobility, multi-object capability and tracking or detecting objects in multiple Degrees Of Freedom (DOFs) in unstructured fields. In this paper, we present a sensor station network designed to overcome these limitations. Our mobile testbed consists of self-powered stations, each equipped with a high-resolution 3D-Light Detection And Ranging (LiDAR) sensor, dual-antenna Global Navigation Satellite System (GNSS) receivers and on-board edge computers. By synchronising over GNSS time and calibrating rigid LiDAR-to-LiDAR transformations, we fuse point clouds from multiple stations into a coherent geometric representation of a real agricultural environment, which we sample at up to 20 Hz. We demonstrate the performance of the system in field experiments with an autonomous robot traversing a 26,000 m² area at up to 20 km/h. Our results show continuous and consistent detections of the robot even at the field boundaries. This work will enable a comprehensive evaluation of geofencing and environmental perception capabilities, paving the way for safety and performance benchmarking of agricultural robot systems. Full article

High-voltage direct current (HVDC) systems, with their advantages of large capacity, long distance, high efficiency, and low loss, are becoming the core support of new power systems. However, in conventional droop control, the fixed droop coefficient causes output power disproportionate to the available capacities among converters, as well as a relatively large deviation of DC voltage in HVDC systems. Therefore, in this paper, a two-objective optimization model for droop control is developed and then it is integrated to a cooperative control, which achieves the co-optimization of voltage deviation and power sharing among multiple converters. In the optimization model, there are two objectives, the minimization of voltage deviation and maximization of the capacity utilization rates of converters. Further, a cooperative control method based on the optimization model is proposed, where information on voltage and power in droop-controlled converters is acquired and the co-optimization of voltage deviation and power sharing is performed to obtain the optimal droop coefficients for these converters, which minimizes voltage deviation, and at the same time, makes power mismatches proportional to their available capacities among converters. Finally, a testbed is built in PSCAD/EMTDC and four cases are designed to verify the proposed method under different settings. The simulation results show that compared with conventional droop control, the voltage deviation is reduced by 71.74% and 67.67% under the cases that a converter is out of service and the three-phase ground fault of a converter occurs. Additionally, when large power fluctuations occur twice, the power mismatches are shared proportionally to their available capacities, which results in the capacity utilization rates of the droop-controlled converters increasing by 24.46% and 18.75%, respectively. Full article

As Industry 4.0 advances, emerging use cases demand 5G NR networks capable of delivering high uplink throughput and ultra-low downlink latency. This study evaluates a 5G link between a LiDAR-equipped unmanned ground vehicle (UGV) and its control unit using a configurable industrial testbed. Based on 3GPP standards and related literature, we identified latency and uplink throughput as key factors for real-time control. Experiments were conducted across different gNB configurations and attenuation levels. The results show that tuning parameters such as CSI, TRS, and SSB significantly improves performance. In this study, we provide a practical analysis of how these parameters influence key metrics, supported by real-world measurements. Furthermore, adjusting the Scheduling Request period and PDCCH candidate settings enhanced uplink reliability. Several configurations supported high LiDAR uplink traffic while maintaining low control latency, meeting industrial 3GPP standards. The configurations also met throughput requirements specified in UAV-related 3GPP standards. In favorable radio link conditions, selected configurations were sufficient to also enable cooperative driving or even machine control. This work highlights the importance of fine-tuning parameters and performing testbed-based evaluations to bridge the gap between simulation and deployment in Industry 4.0. Full article

This paper presents a comprehensive review of tethered unmanned aerial vehicles (UAVs), focusing on their challenges and potential applications across various domains. We analyze the dynamic characteristics of tethered UAV systems and address the unique challenges they present, including complex tether dynamics, impulsive forces, and entanglement risks. Additionally, we explore application-specific challenges in areas such as payload transportation and ground-connected systems. The review also examines existing tethered UAV testbed designs, highlighting their strengths and limitations in both simulation and experimental settings. We discuss advancements in multi-UAV cooperation, ground–air collaboration through tethers, and the integration of retractable tether systems. Moreover, we identify critical future challenges in developing tethered UAV systems, emphasizing the need for robust control strategies and innovative solutions for dynamic and cluttered environments. Finally, the paper provides insights into the future potential of variable-length tethered UAV systems, exploring how these systems can enhance versatility, improve operational safety, and expand the range of feasible applications in industries such as logistics, emergency response, and environmental monitoring. Full article

Multiband and nodal-like superconductivity (SC) with s- + d-wave pairing symmetry have implied that tetragonal iron sulphide (FeS) is a distinctive testbed for exploring unexpected electronic correlations. In particular, the low-moment disordered static magnetism originating from the Fe moment leads to the possibility of the coexistence of magnetic orders (MOs) in the superconducting ground state via the tuning of electronic configurations. Here, guided by density functional theory (DFT) calculations, we found that slightly substitutionally doped chromium (Cr) atoms in tetragonal FeS single crystals can induce both considerable d-orbital reconstruction around the Fermi surface and a local magnetic moment of 2.4 µ_B at each doping site, which could highly modulate the SC ground states of the host. On this basis, a clear magnetic transition and reduced anisotropy of SC were experimentally observed. In particular, SC can survive with a doping content below 0.05. This coexistence of SC and MOs suggests strong spin correlations between Cr dopants and the host through exchange coupling. Further, an electronic temperature-related phase diagram of FeS with Cr doping contents from 0 to 0.07 is also provided. These results demonstrate that the continuous injection of local moments can be a controllable method to use to tune collective orders in unconventional iron-based superconductors. Full article

Current Satellite-Based Augmentation Systems (SBASs) improve the positioning accuracy and integrity of GPS satellites and provide safe civil aviation navigation services for procedures from en-route to LPV-200 precision approach over specific regions. SBAS systems, such as WAAS, EGNOS, GAGAN, and MSAS, already operate. The development of operational SBAS systems is in transition due to the extension of L1 SBAS services to new regions and the improvements expected by the introduction of dual frequency multi-constellation (DFMC) services, which allow the use of more core constellations such as Galileo and the use of ionosphere-free L1/L5 signal combination. The UKSBAS Testbed is a demonstration and feasibility project in the framework of ESA’s Navigation Innovation Support Programme (NAVISP), which is sponsored by the UK’s HMG with the participation of the Department for Transport and the UK Space Agency. UKSBAS Testbed’s main objective is to deliver a new L1 SBAS signal in space (SIS) from May 2022 in the UK region using Viasat’s Inmarsat-3F5 geostationary (GEO) satellite and Goonhilly Earth Station as signal uplink over PRN 158, as well as L1 SBAS and DFMC SBAS services through the Internet. SBAS messages are generated by GMV’s magicSBAS software and fed with data from the Ordnance Survey’s station network. This paper provides an assessment of the performance achieved by the UKSBAS Testbed during the last two years of operations at the SIS and user level, including a number of experimentation campaigns performed in the aviation and maritime domains, comprising ground tests at airports, flight tests on aircraft and sea trials on a vessel. This assessment includes, among others, service availability (e.g., APV-I, LPV-200), protection levels (PL), and position errors (PE) statistics over the service area and in a network of receivers. Full article

A space-borne telescope is used for Earth observation at about 500 km above sea level in the thermosphere where the air density is very low and the temperature increases significantly during daytime. If the telescopes are aligned and characterized on the ground with standard temperature and pressure (STP) conditions, different from that of the thermosphere, their performance could drift during their mission. Therefore, they are usually placed in a thermal vacuum chamber during ground testing in order to verify the system can perform well and withstand the harsh environment such as a high vacuum level and large temperature variations before being launched. Nevertheless, it remains a challenge to build up an in situ optical measurement system for a large aperture telescope in a thermal vacuum chamber due to the finite internal space of the chamber, limited aperture size of the vacuum view port and thermal dissipation problem of the measuring instruments. In this paper, a novel architecture of an interferometer whose light path travels across a vacuum chamber and an atmospheric environment has been proposed to resolve all of these technical issues. The major feature of the architecture is the diverger lens being located within the vacuum chamber, leaving the rest of the interferometer outside. The variation of the interference fringe due to the relocation of the diverger lens has been investigated with optical simulations and the solutions for compensation have also been proposed. Together with a specific alignment procedure for the proposed architecture, the interferogram has been successfully acquired from a prototype testbed. Full article

This paper presents the development of a hardware-in-the-loop ground testbed featuring active gravity compensation via software-in-the-loop integration, specially designed to support research in autonomous robotic removal of space debris. The testbed is designed to replicate six degrees of freedom (6DOF) motion maneuvering to accurately simulate the dynamic behaviors of free-floating robotic manipulators and free-tumbling space debris under microgravity conditions. The testbed incorporates two industrial 6DOF robotic manipulators, a three-finger robotic gripper, and a suite of sensors, including cameras, force/torque sensors, and tactile tensors. Such a setup provides a robust platform for testing and validating technologies related to autonomous tracking, capture, and post-capture stabilization within the context of active space debris removal missions. Preliminary experimental results have demonstrated advancements in motion control, computer vision, and sensor fusion. This facility is positioned to become an essential resource for the development and validation of robotic manipulators in space, offering substantial improvements to the effectiveness and reliability of autonomous capture operations in space missions. Full article

Exploration rovers have difficulty moving underground because the drag force from the ground restricts their movement; this hinders underground exploration. This study aimed to address this challenge. We posit a hypothesis that the rover can move underground by imparting vibration to the ground and changing the drag force. To validate this hypothesis, a testbed that moves underground was developed, and the drag force when imparting vibration was investigated. The results revealed that the drag force while imparting vibration is smaller than that after imparting vibration, and we accordingly devised the operation for moving underground. The proposed operation causes bias of the drag force by imparting vibration to make the testbed move in the direction of the small drag force. The effectiveness of the proposed method was assessed through an experiment wherein the testbed was set to move underground. The experimental results demonstrate the superiority of the proposed method, as the movement distance achieved with vibration is considerably greater than that without vibration. The findings validate the hypothesis that using vibration for underground motion is effective in improving mobility and provides valuable insights into the design of robots for underground motion. Full article

Cemented subsoils, commonly referred to as caliche, pose a regular challenge for agricultural development in arid and semi-arid regions like coastal southern Peru. These subsurface features restrict root penetration, limit water infiltration and hinder essential soil processes, ultimately reducing crop yields and agricultural productivity. Accurate and efficient mapping of caliche is important for optimizing land-use planning and implementing sustainable agricultural practices. This study presents the application of near-surface geophysical techniques for mapping caliche deposits in the context of agricultural development at the future Majes II site in the Arequipa region of southern Peru. Specifically, we employed high-frequency ground-penetrating radar (GPR) and frequency-domain electromagnetics (FDEM) at a testbed on the Majes II site to evaluate their ability to delineate the extent, thickness, and depth of caliche within the local geology. GPR offers high-resolution imaging, effectively capturing sharp contrasts between caliche and surrounding materials, providing detailed information on the thickness (approximately 0.4 m) and the depth (up to 1.5 m) of the caliche layers. FDEM provides valuable insights into the presence of caliche at a faster rate of data acquisition and processing, enabling rapid assessment of the extent of caliche deposits, although with the tradeoff of lower resolution and depth information. We demonstrate that these two geophysical methods can be used separately or in an integrated manner for collaborative interpretation at the Majes II site to inform land management decisions, including identifying areas with favorable conditions for crop production and implementing targeted interventions to mitigate the adverse effects of caliche on agricultural productivity. Full article

With the widespread use of unmanned aerial vehicles (UAVs), the detection and identification of UAVs is a vital security issue for the safety of airspace and ground facilities in the no-fly zone. Telemetry radios are important wireless communication devices for UAVs, especially in UAVs beyond the visual line of sight (BVLOS) operating mode. This work focuses on the UAV identification approach using transient signals from UAV telemetry radios instead of the signals from UAV controllers that the former research work depended on. In our novel UAV Radio Frequency (RF) identification system framework based on telemetry radio signals, the $EC-\alpha$ algorithm is optimized to detect the starting point of the UAV transient signal and the detection accuracy at different signal-to-noise ratios (SNR) is evaluated. In the training stage, the Convolutional Neural Network (CNN) model is trained to extract features from raw I/Q data of the transient signals with different waveforms. Its architecture and hyperparameters are analyzed and optimized. In the identification stage, the extracted transient signals are clustered through the Self-Organizing Map (SOM) algorithm and the Clustering Signals Joint Identification (CSJI) algorithm is proposed to improve the accuracy of RF fingerprint identification. To evaluate the performance of our proposed approach, we design a testbed, including two UAVs as the flight platform, a Universal Software Radio Peripheral (USRP) as the receiver, and 20 telemetry radios with the same model as targets for identification. Indoor test results show that the optimized identification approach achieves an average accuracy of 92.3% at 30 dB. In comparison, the identification accuracy of SVM and KNN is 69.7% and 74.5%, respectively, at the same SNR condition. Extensive experiments are conducted outdoors to demonstrate the feasibility of this approach. Full article

Distributed energy resources and the number of relays are expected to rise in modern electrical grids; consequently, relay misoperations are also expected to grow. Relays can detect electrical fault types using an internal algorithm and can display the result using light indicators on the front of the relay. However, some relays’ internal algorithms for predicting types of electrical faults could be improved. This study assesses a relay’s external and internal algorithms with an Advanced Synchronized Time Digital Grid Twin (ASTDGT) testbed with paired relays. A misoperation relay analysis focused on measuring the accuracy of using the boundary admittance (the external algorithm) versus the set-default (the internal algorithm) relay method to determine the electrical fault types was performed. In this study, the internal and external relay algorithms were assessed with a synchronized time digital grid twin testbed using a real-time simulator. This testbed evaluated two sets of logic at the same time with the digital grid twin and paired relays in the loop. Different types of electrical faults were simulated, and the relays’ recorded events and electrical fault light indicator states were collected from the human–machine interfaces. This ASTDGT testbed with paired relays successfully evaluated the relay algorithm misoperations. The boundary admittance method had an accuracy of 100% for line-to-line, line-to-ground, and line-to-line ground faults. Full article

In recent years, the space industry has witnessed a resurgence, characterized by a notable proliferation of satellites operating at progressively lower altitudes, promising extensive global coverage and terrestrial-level data transfer speeds, while remaining cost-effective solutions. In particular, Wireless Sensor Networks (WSNs) can benefit from the wide coverage of space infrastructure due to their extensive deployment, disrupted communication nature, and the potential absence of terrestrial support. This study explored the utility of Low-Earth Orbit (LEO) satellite constellations as a communication infrastructure for interconnecting “smart” devices via ground stations in Internet of Things (IoT) scenarios. To this end, we designed and implemented a series of experiments conducted within the OMNeT++ simulator, utilizing an updated iteration of the original Open Source Satellite Simulator (OS3) framework. Our research encompassed an IoT Case Study, incorporating authentic sensor data sourced from the Smart Santander testbed. Throughout our experimentation, we investigated the impact of the constellation design parameters such as the number of satellites and orbital planes, as well as the inter-satellite link configuration on the obtained Round-Trip Time (RTT) and packet loss rates. Full article

Given the increase in air traffic, the main challenges in aircraft design are in-flight emissions and noise heard by the community. These problems have thus far been solved by incremental improvements in aerodynamics, engine technology and operation. To dramatically reduce aviation’s carbon footprint towards an environmentally friendly air transport system, alternative propulsion concepts are one of the promising areas of research and first applications. In this context, the goal of integrating a hybrid-electric powertrain with a suitable airframe is to increase efficiency while reducing in-flight emissions, reduce noise for the community, drive down direct operating costs and increase reliability. This article presents an inexpensive approach to testing small, manned aircraft with a hybrid fuel–electric propulsion system. First, the design assumptions of the research flying platform are presented. Next, modifications of the existing two-seater glider are analyzed. These modifications are necessary to fit the fuel–electric hybrid propulsion system. The analysis allows us to select the elements of an appropriate hybrid electric system. It also shows that this type of small experimental propulsion system can be mounted on a two-seater aerobatic glider without significant structural modifications and still comply with the most important points of the Certification Standard-22. Finally, the design of the ground test stand for the propulsion system is described. It is believed that a thorough examination of the propulsion system on the ground will reveal both the advantages and disadvantages of the system. This should facilitate the successful installation of the system under study on a flying aircraft. Full article