Dynamic Hopping Research Articles

Dynamic low earth orbit multi satellite hopping beam resource allocation considering load and dynamic coverage balance (LDCB-MSHBRA)

A dynamic low earth orbit multi satellite hopping beam resource allocation method based on time slicing is proposed to address the issue of changing coverage and beam interference caused by satellite mobility in multi satellite and multi beam communication scenarios. The method involves six processes: (1) Establishing a low earth orbit satellite system with three identical configuration parameters and motion speed parameters; (2)Assign a value to the time slicing weight coefficient and use the principle of load balancing to minimize the difference in demand for dual star services as the optimization objective; (3) Obtain initial power resource allocation with maximum system capacity as the optimization objective; (4) Considering the mobility of low earth orbit satellites, updating weight coefficients and dynamically allocating power resources, a time resource dynamic allocation matrix and the optimal service cell set are obtained; (5) Update the independent coverage cell set of the third low earth orbit satellite, use the Lagrange equation of the weighted fair objective function to obtain the time resource allocation optimization matrix, and use one-way search to determine the optimal service cell set; (6) With the goal of maximizing system capacity, the optimal solution of the power resource allocation matrix for the third low earth orbit satellite is obtained. The system throughput is introduced to intuitively measure system performance, and adjustments are made based on the overlap of Samsung coverage. The resource allocation method is based on a fairness model, considering load balancing and dynamic coverage range changes. On the basis of improving the overall system throughput, it ensures the fairness of resource allocation and allocates time, frequency, and power resources to multiple satellites with overlapping coverage, which helps to improve the throughput and resource utilization of satellite systems.

Future satellite communications: Satellite constellations and connectivity from space

Satellite communications is currently undergoing a massive growth, with a rapid expansion in Low Earth Orbit (LEO) networks, and a range of new satellite technologies. Until very recently, satellite communication systems and terrestrial 5/6G wireless networks have been complementary distinct entities. There is now the opportunity to bring these networks together and deliver an integrated global coverage multi-service network. Achieving this will require solving some key research challenges, and leveraging new technologies including high frequency phased-array antennas, onboard processing, dynamic beam hopping, physical layer signal processing algorithms, transmission waveforms, and adaptive inter-satellite links and routing. By integrating seamlessly with terrestrial 5/6G networks and low altitude flying access points, future satellite networks promise to deliver universal connectivity on a global scale, overcoming geographical limitations. In this special issue, we focus on the future of satellite communications, exploring topics ranging from beam hopping and design to space routing and THz satellite communications. Our aim is to shed light on the potential of these emerging technologies and their role in reshaping the landscape of global connectivity.

Dynamic Beam Hopping and Resource Allocation for Non-Uniform Traffic Demand in NGSO Satellite Communication Systems

Dynamic Beam Hopping and Resource Allocation for Non-Uniform Traffic Demand in NGSO Satellite Communication Systems

Stability Analysis of Passive Monopedal Dynamic Hopping

Stability Analysis of Passive Monopedal Dynamic Hopping

Anomalous Elastic Evolution Induced by Copper Hopping in van der Waals Ferroelectric CuInP2S6

AbstractVan der Waals (vdW) ferroelectric CuInP2S6 (CIPS) has great potential in post‐Moore's law electronics owing to their advantages of weak interlayer interaction, stable surface with free dangling bonds, and robust switchable spontaneous polarization. The flexoelectric effect is demonstrated as an alternative switching method for the design of ferroelectric domains in layered vdW CIPS. However, the investigation of the correlation between the polarization and elastic properties remains indistinct. Here, an elastic evolution is explored experimentally and theoretically in layered vdW CIPS with temperature, of which Young's modulus (EYoung) is determined by analyzing the force‐indentation responses of vdW ferroelectric CIPS. Interestingly, an anomalous leap in EYoung of CIPS from 35 to 65 GPa occurs when the temperature rises across the Curie temperature TC of ≈315 K. Deep potential molecular dynamic (DPMD) simulations identify that this abnormal behavior can be attributed to temperature‐dependent change of copper distribution and the local copper dynamic hopping, intertwined with the order‐disorder ferroelectric phase transition, which is quite different from the typical decrease of EYoung in the lattice constant due to temperature increasing. The exploration provides an important reference for the analysis of coupled mechanical properties and ferroelectricity in CIPS and its applications in flexible electronics.

DDoS attack modeling and resistance using trust based protocol for the security of Internet of Things

The rapid growth of Internet of Things (IoT) devices has led to an increase in security challenges, particularly for wireless sensor networks (WSNs). This work addresses the issue of distributed denial of service (DDoS) attacks in the IoT environment, with a focus on replay attacks. This study introduces a novel technique to counter reactive DDoS attacks in the Internet of Things (IoT) environment. The objective is to enhance the security of the IoT by preventing and mitigating DDoS attacks. The proposed technique involves the use of a dynamic frequency hopping mechanism that shifts the operating frequency of the system in real-time, making it difficult for the attacker to interfere with the system. The simulation-based methodology based on network simulator was employed to evaluate the performance of the proposed technique. Results show that the proposed technique effectively reduces the impact of reactive DDoS attacks by up to 95%, with minimal overhead on the system. The evaluation proved that our work outperforms state-of-the-art schemes such as EDDK and HAPOSCO in terms of computational cost, throughput, and delay. Performance metrics considered in the evaluation include energy consumption, packet loss, and computational time Overall, the study demonstrates the effectiveness of the proposed technique in enhancing the security of IoT systems against reactive attacks.

Passive Dynamic Hopping

Passive Dynamic Hopping

기능적 발목관절 불안정성 축구선수의 신경근 훈련이 발목관절 기능 및 운동 수행능력에 미치는 영향

This study attempted to investigate the functional ankle instability (FAI) of soccer players. In this study, twelve college soccer players were selected as subjects. Before the experiment, based on the ankle joint instability scale (AII, FAAM, idFAI), six subjects with FAI were divided into FAI experimental group, while the other six subjects without FAI were classified as control groups. Firstly, functional movement tests were performed on two groups of subjects, including dynamic balance ability, rear-foot angle and hopping. Then, the two groups of subjects performed neuromuscular training for up to six weeks. When the training was over, we performed the same functional movement tests on both groups. Finally, we analyzed and compared the indicators of the experimental group and the control group before and after the training. The detailed results are as follows: After six weeks of neuromuscular training, there was a tendency for the dorsiflexion of the ankle joint to increase as well as the varus of knee-joint during the drop landing. After six weeks of neuromuscular training, the dynamic stability forward extension of the CON group was increased and the ability of side hop and figure-of-8 hop was improved. After six weeks of neuromuscular training, it was confirmed that the forward extension and figure-of-8 hop in the dynamic stability of the CON group were significantly improved than the FAI group, although we did not point out the differences between the groups before training. These results will provide useful information about the design considered for rehabilitation or prevention of CAI for soccer players.

Orbital hopping maneuvers with two Astrobee free-flyers: Ground and flight experiments.

Dynamic hopping maneuvers using mechanical actuation are proposed as a method of locomotion for free-flyer vehicles near or on large space structures. Such maneuvers are of interest for applications related to proximity maneuvers, observation, cargo carrying, fabrication, and sensor data collection. This study describes a set of dynamic hopping maneuver experiments performed using two Astrobees. Both vehicles were made to initially grasp onto a common free-floating handrail. From this initial condition, the active Astrobee launched itself using mechanical actuation of its robotic arm manipulator. The results are presented from the ground and flight experimental sessions completed at the Spacecraft Robotics Laboratory of the Naval Postgraduate School, the Intelligent Robotics Group facility at NASA Ames Research Center, and hopping maneuvers aboard the International Space Station. Overall, this study demonstrates that locomotion through mechanical actuation could successfully launch a free-flyer vehicle in an initial desired trajectory from another object of similar size and mass.

Model-free reinforcement learning for robust locomotion using demonstrations from trajectory optimization.

We present a general, two-stage reinforcement learning approach to create robust policies that can be deployed on real robots without any additional training using a single demonstration generated by trajectory optimization. The demonstration is used in the first stage as a starting point to facilitate initial exploration. In the second stage, the relevant task reward is optimized directly and a policy robust to environment uncertainties is computed. We demonstrate and examine in detail the performance and robustness of our approach on highly dynamic hopping and bounding tasks on a quadruped robot.

Asymptotically Stable Single‐Legged Passive Dynamic Hopping

Passive dynamic locomotion arises only as a result of dynamic interaction with the ground, that is, without actuators, sensors, or controls. For exploring the principles of human and animal locomotion, passive dynamics is important. One important characteristic is the existence of a stable limit cycle in passive locomotion dynamics. However, to date, no limit cycle has been found in passive dynamic hopping (PDH). Numerical simulation reveals that the leg dynamics of PDH has a stable limit cycle. © 2022 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

Dynamic Beam Hopping for DVB-S2X GEO Satellite: A DRL-Powered GA Approach

Dynamic beam hopping (DBH) is a crucial technology for adapting to the flexibility of service configurations in multi-beam satellite (MBS) communications. To solve the problem that the traditional beam-hopping method is difficult to adapt to the dynamic satellite environment, Deep Reinforcement Learning (DRL) was proposed. DRL can use the previous information to make decisions at the current moment and thus has low time complexity. However, because the generalization ability of the existing DRL methods cannot fully meet dynamic changes in multi-beam satellite communications scenarios, it is difficult to obtain the optimal decision. To address this issue, this letter explores a new framework in which DRL-Powered genetic algorithm (GA) approach. The proposed method uses DRL to assist the decision of DBH. Comparing the proposed method with DRL and traditional GA, simulation results show that the proposed method has a better performance in throughput and fairness when adapting to changes in the satellite environment.

Stability Analysis of a Single-legged Passive Dynamic Hopping

Stability Analysis of a Single-legged Passive Dynamic Hopping

The Impact of Integrating Musical and Image Technology upon the Level of Learning Engagement of Pre-School Children

This study aimed to evaluate the impact of music technology on the attitudes and engagement level of preschool children. The desired outcome of the study is to formulate recommendations to improve the teaching curriculum through the use of physical activities at the preschool level. The strategy tested involved integrating technology, music, and images into children’s physical activities to enhance their willingness to learn, preference, and motor skills. The study used music and images created through technology instruments to stimulate multiple senses, including vision, hearing, and touch sensations. It was expected to enhance learning interests and motor skills among children in physical activities. The innovative courses were developed jointly by qualified and senior preschool teachers, a physical fitness trainer, and a music therapist. The regimen involved a set of lesson plans combining music technology with physical training for children. The study used 64 healthy children who were 5 years old and studied at a private preschool in Taiwan, who were divided into an experimental group that implemented the innovative courses and a control group that adopted traditional teaching. The physical training courses were implemented twice a week, with 45 min per session for 18 weeks. The results revealed a significant enhancement in the concentration, preference, and willingness of participation among children in the experimental group after participation in the course. However, these effects were not observed and were not found among the children in the control group. Additionally, it was also found that the positive impact of enhanced motor skills, such as dynamic balance, hopping, and jumping, was significantly better among children in the experimental group than those in the control group. Consequently, this research study supports the integration of music technology and images into physical courses for children. Clinically, it indicates a significantly improved enhancement effect towards learning mentality and motor skills among children. This innovative teaching approach suggests a high probability to substantially assist the preschool’s course management strategy and methodical learning effects.

Dynamic Beam Hopping Time Slots Allocation Based on Genetic Algorithm of Satellite Communication under Time-Varying Rain Attenuation

Beam hopping technology is considered to provide a high level of flexible resource allocation to manage uneven traffic requests in multi-beam high throughput satellite systems. Conventional beam hopping resource allocation methods assume constant rainfall attenuation. Different from conventional methods, by employing genetic algorithm this paper studies dynamic beam hopping time slots allocation under the effect of time-varying rain attenuation. Firstly, a beam hopping system model as well as rain attenuation time series based on Dirac lognormal distribution are provided. On this basis, the dynamic allocation method by employing genetic algorithm is proposed to obtain both quantity and arrangement of time slots allocated for each beam. Simulation results show that, compared with conventional methods, the proposed algorithm can dynamically adjust time slots allocation to meet the non-uniform traffic requirements of each beam under the effect of time-varying rain attenuation and effectively improve system performance.

Detection of dynamic location primary user emulation on mobile cognitive radio networks using USRP

The study and the detection of possible network attacks are essential for wireless networks, in particular for mobile cognitive radio networks due to its characteristics such as the dynamic spectrum allocation and constant frequency hopping. The primary user emulation attack is one of the most significant attacks in cognitive radio, because it hazards the complete cognitive cycle. The techniques used for the detection of primary user emulation found in the literature are based on a fixed attacker location. However, in a mobile environment, the attacker usually has dynamic locations and this compromises the current applied security techniques and generates inefficient attack detection. Therefore, our work proposes a novel technique using cross-layer design for the detection of primary user emulation with mobility. This attack detection technique was tested with experiments using software-defined radio equipment and mobile phones at indoor scenarios with dynamic locations and with a mobile phone base station built up also with software-defined radio. The obtained results show that the combination of the three utilized techniques, energy detection, motion estimation, and application information analysis, are able to optimize the detection with around 100% of effectiveness for the primary user emulation attack with dynamic location. The proposed technique shows that the energy detection time is around 100 ms and for the processing time of the information analysis in the mobile phone is about 30 s. This result shows a practical and effective approach to detect primary emulation attacks. The proposed technique, to the best of the authors’ knowledge, has not been presented before in the literature with experiments neither with mobility conditions of the attacker as presented in our proposed work.

Series Elastic Behavior of Biarticular Muscle-Tendon Structure in a Robotic Leg.

We investigate the role of lower leg muscle-tendon structures in providing serial elastic behavior to the hip actuator. We present a leg design with physical elastic elements in leg angle and virtual leg axis direction, and its impact onto energy efficient legged locomotion. By testing and comparing two robotic lower leg spring configurations, we can provide potential explanations of the functionality of similar animal leg morphologies with lower leg muscle-tendon network structures. We investigate the effects of leg angle compliance during locomotion. In a proof of concept, we show that a leg with a gastrocnemius inspired elasticity possesses elastic components that deflect in leg angle directions. The leg design with elastic elements in leg angle direction can store hip actuator energy in the series elastic element. We then show the leg's advantages in mechanical design in a vertical drop experiment. In the drop experiments the biarticular leg requires 46% less power. During drop loading, the leg adapts its posture and stores the energy in its springs. The increased energy storing capacity in leg angle direction reduces energy requirements and cost of transport by 31% during dynamic hopping to a cost of transport of 1.2 at 0.9 kg body weight. The biarticular robot leg design has major advantages, especially compared to more traditional robot designs. Despite its high degree of under-actuation, it is easy to converge into and maintain dynamic hopping locomotion. The presented control is based on a simple-to-implement, feed-forward pattern generator. The biarticular legs lightweight design can be rapidly assembled and is largely made from elements created by rapid prototyping. At the same time it is robust, and passively withstands drops from 200% body height. The biarticular leg shows, to the best of the authors' knowledge, the lowest achieved relative cost of transport documented for all dynamically hopping and running robots of 64% of a comparable natural runner's COT.

Image encryption and watermarking combined dynamic chaotic hopping pattern with double random phase encoding DRPE

In modern civilization information, security is a crucial problem. Image encryption and watermarking can effectively protect information from unauthorized access. This paper introduces a new vigorous symmetric optical image encryption and watermarking technique. This technique depends on a novel dynamic delay chaotic hopping pattern (DDCHP) combined with double random phase encoding (DRPE). To get a robust watermark image, the plain image is first watermarked with a binary secret message using a new chaotic hopping pattern (CHP) and then encrypted using a DRPE system that is controlled by double random independent keys generated with double DDCHP. In this symmetric cryptosystem, three different chaotic maps are used to enlarge the key space of the proposed cryptosystem against brute-force attack and overcome the linearity and vulnerable of the classical DRPE. The system keys are hypersensitive and their initial parameters are selected carefully. Security scrutiny proves the efficiency of the suggested cryptosystem. Therefore, the obtained simulation results prove that the cryptosystem is robust enough against the known attacks, such as statistical attack (uniform histograms of different encrypted images, correlation coefficients between the plain and the encrypted image is as low as 5.46 × 10−6), differential attack (99.99% NPCR and 38.6% UACI), brute force attack (large enough key space), and entropy attack. Moreover, the robustness of the watermark (secret message) is proved due to the solidity of CHP. The proposed approach can be used in different implementations like secure military communications, e-finance, e-healthcare, authenticated multimedia broadcasting, etc.

Hamstring Muscle Activity After Primary Anterior Cruciate Ligament Reconstruction-A Protective Mechanism in Those Who Do Not Sustain a Secondary Injury? A Preliminary Study.

Individuals who experience a subsequent ipsilateral anterior cruci (cruciate)ate ligament (ACL) reinjury may use hazardous muscle activation strategies after primary ACL reconstruction (ACLR). The purpose of this study was to compare electromyograms (EMGs) of the quadriceps, hamstrings, and gastrocnemius muscles during a dynamic hopping task among individuals with a single ACL injury (ACLx1), individuals who went on to have secondary ipsilateral ACL injury (ACLx2), and individuals who have never sustained an ACL injury (ACLx0). We expected that individuals who went on to experience a secondary ACL injury would use less quadriceps muscle activity as compared with individuals who experienced a single ACL injury. Cross-sectional study. Level 3. Fourteen individuals that were returned to play post-ACLR and 7 non-ACL-injured individuals participated. Individuals who had undergone an ACLR were placed into groups depending on whether they had experienced a secondary ipsilateral ACL reinjury postprimary ACLR. EMG data of the vastus lateralis, biceps femoris, and lateral gastrocnemius were measured during 2 phases of a single-leg dynamic hopping task: preactivity (100 ms prior to ground contact) and reactivity (250 ms post-ground contact). Processed EMG data were compared across groups using 1-way analyses of variance, with post hoc independent t tests where appropriate (P ≤ 0.05). At preactivity, ACLx1 (0.48% ± 0.2%max) was found to use significantly more hamstring activity than ACLx2 (0.20% ± 0.1%max, P = 0.018), but not than ACLx0 (0.38% ± 0.1%max, P > 0.05). At reactivity, both ACL groups were found to use less quadriceps activity than ACLx0 (ACLx1: 0.38% ± 0.1%max, P = 0.016; ACLx2: 0.40% ± 0.1%max, P = 0.033; ACLx0: 0.58% ± 0.1%max), but not than each other (P > 0.05). Quadriceps muscle activity during landing was diminished in all ACL participants as compared with participants who had never sustained an ACL injury. Individuals who did not experience a secondary ipsilateral ACL reinjury (ACLx1) used greater levels of hamstring activity prior to landing. The higher hamstring activity in patients who did not experience a secondary injury may be interpreted as a protective mechanism that is used to dynamically stabilize the reconstructed limb.

Model-based open loop control of a multigait legged underwater robot

In this paper a model-based open loop control of SILVER, a multigait legged underwater vehicle for the benthic zone exploration, is presented. The contributions of underwater environment are taken into account by resorting to a recently introduced fundamental model of monopedal underwater hopping locomotion on which the tuning of a completely open loop control algorithm for dynamic gaits is based. The design of the robot and the control algorithm of each gait are presented along with experimental results which demonstrate on-spot static and dynamic rotation, and forward locomotion by crawling, walking and hopping. Moreover, for the first time the behavior of multi-legged underwater robots is grounded to the fundamental monopedal model. SILVER is the first underwater legged robot capable of performing dynamic self-stabilizing hopping gaits together with static gaits and precise foot placement. Thanks to its unique features the category of underwater legged robots has the potential to be a very versatile and valuable alternative to the existing technology for the exploration of the seabed.