Link Loss Research Articles

So close and yet so far: Comparing the experiences of university non-traditional students before and after the pandemic

This paper explores the impact of the COVID-19 pandemic on the objective and subjective experiences of working-class non-traditional students in Higher Education (HE). Against the backdrop of increased access to tertiary education, the study delves into the challenges faced by historically under-represented groups, analyzing educational vulnerabilities and inequalities. More specifically, the contribution analyses how the pandemic scenario change students’ experience—in terms of the emergence of new forms of inequality—. With this aim, the research involves 20 in-depth interviews with working-class non-traditional students in a Catalan public university before the pandemic (2018) and 12 interviews after the pandemic (2022). Results reveal that while these students already encountered significant hurdles before the pandemic, the crisis further amplified difficulties, hindering their academic success and deepening pre-existing inequalities. Unexpectedly, elements initially designed to facilitate the situation, such as non-presential teaching, contributed to an unsatisfactory experience, fostering isolation and loss of specific links and codes within the academic field. The findings underscore the pandemic’s detrimental effects on European HE systems, representing a setback in terms of equity and a substantial loss of opportunities for non-traditional students.

MDM‐Incorporated Quad Donut Modes OCDMA‐FSO Scheme for Secure High‐Altitude Platforms‐To‐Satellite Scenarios

ABSTRACTThe next generation of communication networks is envisioned to be driven by high‐altitude platform (HAP)‐to‐satellite systems. License‐free narrow beam free space optics (FSO) can provide uninterrupted connectivity in satellite‐enabled Internet of Things scenarios. This work proposes a HAP‐to‐satellite hybrid mode division multiplexing–optical code division multiple access (MDM‐OCDMA) scheme employing zero cross‐correlation (ZCC) and multidiagonal (MD) codes. In high‐speed satellite communications, a 12 × 10‐Gbps hybrid MDM‐OCDMA scheme carrying four donut modes (0, 1, 2, and 3) enables high channel capacity, sufficient spectral efficiency, and data security under severe link conditions. Based on simulations, the hybrid MDM‐OCDMA scheme using the ZCC code achieves a greater FSO link distance of 420 m compared with when using the MD code at a 10e‐9 error correction limit under clear air and weak turbulent scenario. The reliable transmission distance of 250 m is achievable with the 120‐Gbps proposed system, assuming pointing errors of 2 mrad, 1‐dB receiver, and 2.5‐dB transmitter losses. The results also show that the system can sustain an additional loss of 1.5–2 dB over 250 m for all donut modes. Additionally, the system using ZCC code contributes to low power consumption over MD and variable weight ZCC code and thus requires a minimum received power of −4.02 dBm. It also offers high optical signal to noise of 42–52 dB, −11.58 to −22.20 dB of gain, 11.58–22.20 dB of noise figure, and −48.11 to −58.73 dBm of signal power at output over 200–700 m range up to 2 dB of additional loss. Comparative analysis indicates that the proposed system is more efficient, less complex, adequately distance‐friendly (=420 m), and capable of higher data rates (=120 Gbps) compared with other works. This makes it a promising solution for future high‐speed satellite communications considering the impact of link losses and atmospheric conditions.

Field trial of stable radio frequency transfer system in 200 km metropolitan optical fiber link.

In this paper, we demonstrate stable radio frequency (RF) transfer via metropolitan optical fiber link in the Beijing area. The phase variation of the RF signal is compensated by a phase conjugation method incorporating two high-performance phase-locked loops. The wavelength conversion module extends the transmission length to 200 km with only two parallel 50 km dark optical fibers available. We optimize the configuration of dispersion compensation and optical amplification due to the high loss (0.31 dB/km) of the optical fiber link. At the same time, comparative experiments verify the short-term instability limitation that arises from the group velocity dispersion of the optical fiber link. The measured standard Allan deviation of the 2.4GHz RF transmission system with dispersion compensation is 4.5 × 10-14/1 and 2.6 × 10-17/20 000s, which is superior to that of the reference rubidium clock. The short-term instability of the system is deteriorated to 2.5 × 10-13/1s without dispersion compensation.

A Universal Model for Ultrasonic Energy Transmission in Various Media.

This study presents a comprehensive model for ultrasonic energy transfer (UET) using a 33-mode piezoelectric transducer to advance wireless sensor powering in challenging environments. One of the advantages of UET is that it is not stoppable by electromagnetic shielding and can penetrate metal. Existing models focus on feasibility and numerical analysis but lack an effective link between input and output power in different media applications. The proposed model fills this gap by incorporating key factors of link loss, including resonant frequency, impedance matching, acoustic coupling, and boundary conditions, to predict energy transfer efficiency more accurately. The model is validated through numerical simulations and experimental tests in air, metal, and underwater environments. An error analysis has shown that the maximum error between theoretical and experimental responses is 3.11% (air), 27.37% (water), and 1.76% (aluminum). This research provides valuable insights into UET dynamics and offers practical guidelines for developing efficient wireless powering solutions for sensors in difficult-to-access or electromagnetically shielded conditions.

Distributed optimal scheduling for EVs charging and discharging: A penalty-based consensus approach

In preparing for the widespread adoption of electric vehicles (EVs), this paper investigates a two-stage optimization problem with priority for EV charging and discharging scheduling, while taking into account power load stability, economic objectives, and technical constraints of the distribution network. To this end, a distribution power system integrating energy source and EV owners is modeled. Considering the disturbance or even loss of the communication link, a periodical connected topology is adopted for information exchange among EV owners with the deployed smart meters, which is substantially different from the existing works. The main challenges of the problem are that the information flow among EV owners is time-varying and asymmetric, and each EV owner’s demand should be satisfied throughout the whole scheduling horizon. A novelty distributed hierarchical optimal algorithm, combined with iterative water-filling-based method and penalty-based consensus method, is proposed for the two-stage optimization problem with priority. The convergence and optimality of the algorithm are presented mathematically. In addition, the proposed method combined with receding horizon optimization is performed for EVs random arrival and departure scenarios in the system. Finally, we demonstrate advantages of the proposed algorithm in both theory and simulation.

Relative intensity noise management and thermal/shot noise control for high speed ultra high bandwidth fiber reach transmission performance

Abstract This work has clarified the relative intensity noise management and thermal/shot noise control for high speed ultra high bandwidth fiber reach transmission performance. Total link losses variations are clarified against ambient temperature and relative refractive index difference variations at 1,550 nm wavelength, 20 km fiber link length, and 45 % fluoride dopant ratio inside the fiber material cable. Besides the total link losses variations are demonstrated versus fiber link length and relative refractive index difference variations at 1,550 nm wavelength, room temperature, and 45 % fluoride dopant ratio inside the fiber material cable. Required optical signal per noise ratio (OSNR), electronic signal to noise ratio (SNR), and optimum gain variations are measured and analyzed versus the fiber link length and relative refractive index difference variations at 1,550 nm wavelength, room temperature, and 45 % fluoride dopant ratio inside the fiber material cable.

Impact of hurricane disturbance on mycorrhizal co-occurrence networks: Resilience and community dynamics in the Neotropics

Extreme climatic events and related disturbances such as hurricanes are increasingly altering forest ecosystems. How these events impact forest fungal communities is poorly characterized. We examined the effect of a hurricane on mycorrhizal community structure and potential interspecific fungal interactions, inferred from OTU co-occurrences. We characterized the root fungal communities of dual-mycorrhizal plants from nine plots during two consecutive years after a category four hurricane impacted the coastal Mexican Pacific tropical forest in Jalisco. Presence-abundance matrices were used to calculate properties of mycorrhizal networks including nestedness and modularity, and to infer patterns of co-occurrence. One year after the hurricane there was a loss of links between plants and fungi. Increased network modularity and connectivity were observed after two years. We also found that disturbance changed arbuscular mycorrhizal fungal network structure more strongly than ectomycorrhizal fungal networks. Fungal guilds changed their putative interspecific interactions, from mutual exclusion in the first year to a significant increase in co-occurrence of plant pathogens, saprotrophs, and endophytes in the second year. Our results suggest that in the short term, rhizospheric interactions can be resilient to hurricanes, but fungal guilds may have divergent responses.

Efficient Unsupervised Community Search with Pre-Trained Graph Transformer

Community search has aroused widespread interest in the past decades. Among existing solutions, the learning-based models exhibit outstanding performance in terms of accuracy by leveraging labels to 1) train the model for community score learning, and 2) select the optimal threshold for community identification. However, labeled data are not always available in real-world scenarios. To address this notable limitation of learning-based models, we propose a pre-trained graph Trans former based community search framework that uses Zero label (i.e., unsupervised), termed TransZero. TransZero has two key phases, i.e., the offline pre-training phase and the online search phase. Specifically, in the offline pre-training phase, we design an efficient and effective community search graph transformer ( CSGphormer ) to learn node representation. To pre-train CSGphormer without the usage of labels, we introduce two self-supervised losses, i.e., personalization loss and link loss, motivated by the inherent uniqueness of node and graph topology, respectively. In the online search phase, with the representation learned by the pre-trained CSGphormer , we compute the community score without using labels by measuring the similarity of representations between the query nodes and the nodes in the graph. To free the framework from the usage of a label-based threshold, we define a new function named expected score gain to guide the community identification process. Furthermore, we propose two efficient and effective algorithms for the community identification process that run without the usage of labels. Extensive experiments over 10 public datasets illustrate the superior performance of TransZero regarding both accuracy and efficiency.

Nonlinear spreading behavior across multi-platform social media universe.

Understanding how harmful content (mis/disinformation, hate, etc.) manages to spread among online communities within and across social media platforms represents an urgent societal challenge. We develop a non-linear dynamical model for such viral spreading, which accounts for the fact that online communities dynamically interconnect across multiple social media platforms. Our mean-field theory (Effective Medium Theory) compares well to detailed numerical simulations and provides a specific analytic condition for the onset of outbreaks (i.e., system-wide spreading). Even if the infection rate is significantly lower than the recovery rate, it predicts system-wide spreading if online communities create links between them at high rates and the loss of such links (e.g., due to moderator pressure) is low. Policymakers should, therefore, account for these multi-community dynamics when shaping policies against system-wide spreading.

Investigation of 16 × 10 Gbps mode division multiplexed enabled integrated NGPON–FSO architecture under wired-wireless link losses

Abstract To enhance the transmission capacity for energy consumption and low cost system, mode division multiplexing (MDM) using mode 0 and mode 1 is proposed and investigated. A pair of eight downlink and uplink wavelengths is transmitted by using each MDM mode in an integrated bidirectional next generation passive optical network and free space optics (NGPON–FSO) system at 10 Gbps per channel transmission rate under the impact of FSO–fiber links impairments. Simulation results indicate that received power of −21.2 dBm with 0.2 dB power penalty can be obtained over 1 km FSO and 100 m multimode fiber under unfavourable turbulent effects. The system provides extended FSO link range, and fiber range of 150 km and 600 m respectively at threshold limit of 10−3. Besides, the mathematical analysis depicts the receiver sensitivity and splitter power budget of 42 dBm and 18 dB, respectively, for the proposed system. The system offers finest performance than other pre-existing systems.

Realization of 4 × 200 Gbps 4-QAM OFDM-OWC System Using Higher Order OAM Modes for HAP-to-Satellites Scenario

Recently, there has been an increase in interest in using optical wireless communication (OWC) links on high-altitude platforms (HAPs) for satellite applications. We implement an orbital angular momentum (OAM) multiplexed orthogonal frequency division multiplexing (OFDM) system using an OWC link. A space-to-air scenario is considered in which transmission pointing errors, geometric loss, turbulence, and additional link losses are taken into account to extend the transmission range, system capacity, and throughput. At 200 Gbps per channel data rate, four different OAM modes are implemented with higher order Laguerre–Gaussian (LG) modes of [0,0], [0,13], [0,40], and [0,80]. An aggregate 800 Gbps data rate can deliver a maximum OWC range of 3300–5000 km for all channels. The maximum received power over the 1000 km range is −19.34 to −32.59 dBm with an additional gain of 0–2.5 dB. It is also possible to obtain a better performance over large distances of 500–3500 km with an error vector magnitude of 2.98–17.5%. Furthermore, a high gain of −40.80 dB, a signal-to-noise ratio (SNR) of 55.21 dB, and an optical SNR of 67.25 dB can be achieved for varied transmitter pointing errors of 0.1 rad. As compared to other literature, this system exhibits a superior performance.

LEO Satellite Downlink Distributed Jamming Optimization Method Using a Non-Dominated Sorting Genetic Algorithm

Due to their low orbit, low-Earth-orbit (LEO) satellites possess advantages such as minimal transmission delay, low link loss, flexible deployment, diverse application scenarios, and low manufacturing costs. Moreover, by increasing the number of satellites, the system capacity can be enhanced, making them the core of future communication systems. However, there have been instances where malicious actors used LEO satellite communication equipment to illegally broadcast events in large sports stadiums or engage in unauthorized leakage of military secrets in sensitive military areas. This has become an urgent issue in the field of communication security. To combat and prevent abnormal and illegal communication activities using LEO satellites, this study proposes a LEO satellite downlink distributed jamming optimization method using a non-dominated sorting genetic algorithm. Firstly, a distributed jamming system model for the LEO satellite downlink is established. Then, using a non-dominated sorting genetic algorithm, the jamming parameters are optimized in the power, time, and frequency domains. Field jamming experiments were conducted in the southwest outskirts of Xi’an, China, targeting the LEO constellation of the China Satellite Network. The results indicate that under the condition that the jamming coverage rate is no less than 90%, the proposed method maximizes jamming power, minimizes time delay, and minimizes frequency compensation compared to existing jamming optimization methods, effectively improving the real-time jamming performance and success rate.

Perancangan Jaringan Fiber To The Home Berbasis Gigabit Passive Optical Network Di Citra Garden Puri Cluste Denza

This research aims to design a GPON-based Fiber to The Home (FTTH) line in the Citra Garden Puri cluster Denza . The method used is to carry out field observations, by conducting surveys to determine the need for equipment that will be used in designing the route. After the survey is conducted, this project requires Google Earth Pro software to do the mapping of the spot that is used for the ODP and to create passages for the fiber. To make sure that all planning already meets the requirement, there are several calculationdone in this research such as; link loss budget, power link budget, power margin and risetime budget. The distance that were used in the calculation are calculated from the STO Cengkareng until the ONT on each customer. Based on the calculation, the result of the biggest loss for link loss budget are obtained from the upstream, in the amount of 22,0456 dB and the loss from downstream are equals to 21,5721 dB. The result that obtained for the upstream loss of power link budget are equals to -17,0456 dBm and -16,5172 dBm for downstream. The next calculation is power margin, from this project we obtained the lowest power margin for the upstream 6,9544 dB and 7,4288 dB for downstream. The last calculation obtained for this project is rise time budget, from the calculation the shortest data for the rise time budget upstream is 0,1001 ns and for the downstream is 0,1019 ns. Based on all the calculation, this project can be concluded as a success because all the calculation are between the boundary that is tolerated by PT Telkom.

Deep Immunophenotyping Unveils Depletion of Anti-inflammatory T-helper Type-2 Cells (Th2) and Links Loss of Alternatively-Activated-Monocytes (M2) to Vasospasm and Delayed Cerebral Ischemia Following Subarachnoid Hemorrhage

Deep Immunophenotyping Unveils Depletion of Anti-inflammatory T-helper Type-2 Cells (Th2) and Links Loss of Alternatively-Activated-Monocytes (M2) to Vasospasm and Delayed Cerebral Ischemia Following Subarachnoid Hemorrhage

Performance Analysis of a Single Light Source Bidirectional Visible Light Communication Reverse Reflection Link

Visible light communication has the advantages of large bandwidth, high security, and no RF interference, among which LED light sources are an important light source for indoor visible light communication. The use of LED as a light source for visible full-duplex communication is both to meet the lighting requirements and to ensure high-speed transmission of information. The uplink using the “cat’s eye” reverse modulation system can greatly reduce the system complexity of the reverse reflector. In order to analyze the factors affecting the optical power at the receiving end of the uplink of the indoor single light source visible light communication, this paper establishes the indoor visible light full-duplex communication system model and deduces the calculation method of the effective incidence angle of the uplink transmission light and the movable range of the reverse reflection end according to the model. The results show that when the link distance of the BK7 lens is 3 m, the lens aperture is increased from 100 mm to 150 mm, the lens focal length is increased from 100 mm to 150 mm, the travel distance of the reverse reflector is increased by 60%, and the effective range of the incidence angle is increased by about twice. In the absence of link loss, each 1 m increase in link distance increases the maximum travel distance of the reverse reflector by 0.8 m. Increasing the lens aperture, decreasing the focal length, and increasing the link distance can improve the movable range of the reverse reflector, and the effective incidence angle changes more gently with the position of the reverse reflector.

My synthetic wingman must understand me: modelling intent for future manned–unmanned teaming

With advances in artificial intelligence, machine learning, and cognitive modelling, unmanned aircraft are expected to act as human-like wingmen in the near future. For fluent and effective manned–unmanned teaming, synthetic wingmen must be able to account for and adapt to their partners’ intent with little or no communication. To enable such abilities, it becomes crucial to identify the requirements that makes intent explainable to synthetic wingmen, necessitating approaches to describe and analyse intent from a human-centric perspective. To address this issue, this paper reports on findings from using Work Domain Analysis to design and analyse models of situated intent with six levels of cognitive control (frames, effects, values, generic, implementations, and physical). Through a literature review and seven subject matter expert interviews, a synthesized model was designed to represent fighter pilots’ intent in a manned–unmanned teaming scenario. Using the synthesized model as the context, a transfer of control and a link loss situation were further described and analysed. Experiences show that Work Domain Analysis can provide a practical and applicable means to model situated intent, particularly since designed models can be re-utilised to model intent in similar situations. Furthermore, the model analyses show the importance of accounting for fighter pilots’ adopted frames since small variations of the framing of the situations can propagate throughout the model resulting in conflicting or inconsistent intent. The paper concludes that synthetic wingmen must be able to reason about all six levels of cognitive control, requiring a more holistic approach to make intent explainable.

Impact of flail chain characteristics on productivity, costs, bark content and fuel use when processing short-rotation Eucalyptus globulus trees to produce woodchips

ABSTRACT Infield chipping harvest systems are widely used in Australia and overseas to produce woodchips for pulp production from short-rotation plantations because they can produce uniform woodchips at low cost with high productivity from small trees. Flail chains are used in these systems to remove leaves, small branches and bark prior to chipping because these components are undesirable in paper products. Flail chains wear during use and lose links, requiring chains to be replaced. A range of flail chains is available but the most recent studies comparing flail chain performance were conducted over 30 years ago. The aim of the present study was to address this knowledge gap by comparing the performance of five flail chain types currently in use in terms of their impact on flail productivity, fuel use, woodchip bark content, chain wear and chain replacement costs. The study was conducted on a Husky Precision 2300–4 flail operating in 13-year-old Eucalyptus globulus plantations in southwest Western Australia producing export woodchips. No significant differences were found between the studied flail chains in terms of woodchip bark content, flail productivity or flail fuel use. In all cases, bark content met company standards (<0.5%). Significant differences were found between the studied flail chains in terms of their wear, link losses and replacement costs. Chain replacement costs as a proportion of total flail costs were found to be considerably lower (<1% to 4%) than those reported in previous studies (>20%).

Exploiting NOMA and RIS in Integrated Sensing and Communication

A novel integrated sensing and communication (ISAC) system is proposed, where a dual-functional base station is utilized to transmit the superimposed non-orthogonal multiple access (NOMA) communication signal for serving communication users and sensing targets simultaneously. Furthermore, a new reconfigurable intelligent surface (RIS)-aided-sensing structure, where a dedicated RIS is deployed to provide virtual line-of-sight (LoS) links for radar targets, is also proposed to address the significant path loss or blockage of LoS links for the sensing task. Based on this setup, the beampattern gain at the RIS for the radar target is derived and adopted as a sensing metric. The objective of this paper is to maximize the minimum beampattern gain by jointly optimizing active beamforming at the base station (BS), power allocation coefficients among NOMA users and passive beamforming at the RIS. To tackle the non-convexity of the formulated optimization problem, the beampattern gain and constraints are first transformed into more tractable forms. Then, an iterative block coordinate descent (IBCD) algorithm is proposed by employing successive convex approximation (SCA), Schur complement, semidefinite relaxation (SDR) and sequential rank-one constraint relaxation (SRCR) methods. To reduce the complexity of the proposed IBCD algorithm, a low-complexity iterative alternating optimization (IAO) algorithm is proposed. Particularly, the active beamforming is optimized by solving a semidefinite programming (SDP) problem and the closed-form solutions of the power allocation coefficients are derived. Numerical results show that: i) the proposed RIS-NOMA-ISAC system always outperforms the RIS-ISAC system without NOMA in beampattern gain and illumination power; ii) the low-complexity IAO algorithm achieves a comparable performance to that achieved by the IBCD algorithm. iii) high beampattern gain can be achieved by the proposed joint optimization algorithms in underloaded and overloaded communication scenarios.

Vision-Assisted Millimeter-Wave Beam Management for Next-Generation Wireless Systems: Concepts, Solutions, and Open Challenges

Beamforming techniques have been widely used in the millimeter-wave (mm-wave) bands to mitigate the path loss of mm-wave radio links as narrow straight beams by directionally concentrating the signal energy. However, traditional mm-wave beam management algorithms usually require excessive channel state information (CSI) overhead, leading to extremely high computational and communication costs. This hinders the widespread deployment of mm-wave communications. By contrast, the revolutionary vision-assisted beam management system concept employed at base stations (BSs) can select the optimal beam for the target user equipment (UE), based on location information determined by machine learning (ML) algorithms applied to visual data, without requiring channel information. In this article, we present a comprehensive framework for a vision-assisted mm-wave beam management system, its typical deployment scenarios, and the specifics of the framework. Then, some of the challenges faced by this system and their efficient solutions are discussed from the perspective of ML. Next, a new simulation platform is conceived to provide both visual and wireless data for model validation and performance evaluation. Our simulation results indicate that vision-assisted beam management is indeed attractive for next-generation wireless systems.

Coexistence of Quantum and 1.6 Tbit/s Classical Data Over Fibre-Wireless-Fibre Terminals

In this paper a fibre free-space fibre link that allows a quantum key distribution (QKD) signal and high-speed data to be transmitted in a single optical beam is presented. This setup has the potential to provide ultra-high data rate secure wireless connectivity within indoor spaces. Both quantum and classical channels were transmitted using wavelengths in the C band, over a range of 2.5 m in free space and in the presence of a 200 lx background illumination. Raman noise caused by the light propagating in the optical fibres which provide connections to the free-space segment, together with geometric loss of the free-space link are the major impairments. Results yield secret key rates of 2.343 kbit/s when the QKD signal is sent without high-speed data (and associated Raman noise), and rates of 1.305 - 1.996 kbit/s when high-speed data is also transmitted (depending on spectral separation of QKD and classical information). Further, it is shown that the secret key rate can be optimised by increasing loss to attenuate the Raman noise by misalignment of the link. Improvement of the secret key rate from 1.305 kbit/s to 1.887 kbit/s was shown using this method.