Link Loss Research Articles

A Novel Geometry-Based 3-D Wideband Channel Model and Capacity Analysis for IRS-Assisted UAV Communication Systems

Intelligent reflecting surface (IRS) composed of a large number of low-cost passive reflecting elements has attracted significant attention from communication communities because of its ability to substantially improve the communication performance. In this paper, the aperture area and radiation pattern of the IRS reflecting elements are considered, and a novel geometry-based three-dimensional (3-D) wideband channel model is proposed for IRS-assisted unmanned aerial vehicle (UAV) communication systems. In the proposed model, the reflection phase is designed by jointly considering the aperture area of the IRS reflecting element and the propagation phases among UAV, IRS, and receiver (Rx), each IRS reflecting element is modeled as an anomalous reflector instead of a specular reflector, and large-scale IRS reflecting elements can jointly beamform the signal in a desired direction. Based on the proposed model, the effects of arbitrary trajectory of UAV and the number and the size of passive reflecting elements on channel statistical characteristics are considered, and the average received signal power and the ergodic sum capacity, which consider the impacts of the number and the size of passive reflecting elements, are also investigated. Furthermore, the path loss of the IRS-assisted link, which is in inverse proportion to the square of aperture area of IRS reflecting elements, is derived, and it coincides with the measured results in real outdoor scenarios. Analysis shows that the communication performance can be enhanced by increasing the number and the size of IRS reflecting elements, and it is validated by numerical results and Monte-Carlo simulation results.

Two-Stage Link Loss Optimization of Divergent Gaussian Beams for Narrow Field-of-View Receivers in Line-of-Sight Indoor Downlink Optical Wireless Communication (Invited)

The predominant focus of research in high-speed optical wireless communication (OWC) lies in line-of-sight (LOS) links with narrow infrared beams. However, the implementation of precise tracking and steering necessitates delicate active devices, thereby presenting a formidable challenge in establishing a cost-effective wireless transmission. Other than using none-line-of-sight (NLOS) links with excessive link losses and multi-path distortions, the simplification of the tracking and steering process can be alternatively achieved through the utilization of divergent optical beams in LOS. This paper addresses the issue by relaxing the stringent link budget associated with divergent Gaussian-shaped optical beams and narrow field-of-view (FOV) receivers in LOS OWC through the independent optimization of geometrical path loss and fiber coupling loss. More importantly, the geometrical path loss is effectively mitigated by modifying the transverse intensity distribution of the optical beam using manipulations of multi-mode fibers (MMFs) in an all-fiber configuration. In addition, the sufficiently excited higher order modes (HOMs) of MMFs enable a homogenized distribution of received optical powers (ROPs) within the coverage area, which facilitates the mobility of end-users. Comparative analysis against back-to-back links without free-space transmission demonstrates the proposed scheme’s ability to achieve low power penalties. With the minimized link losses, experimental results demonstrate a 10 Gbps error-free (BER < 10−13) LOS OWC downlink transmission at 2.5 m over an angular range of 10° × 10° without using any optical pre-amplifications at a typical PIN receiver. The proposed scheme provides a simple and low-cost solution for high-speed and short-range indoor wireless applications.

Barycentric coordinate-based distributed localization for wireless sensor networks subject to random lossy links

Distributed localization in wireless sensor networks is essential for verifying the positions of the sensor nodes deployed in the sensing field based on information interactions. However, the information transmitted from the controller to the actuator for each sensor node may be lost owing to communication noise, channel interference, or network congestion. With this in mind, this paper aims at investigating the distributed localization for wireless sensor networks subject to random lossy links. The barycentric coordinate, which can be determined by the distance measurements between node pairs in the network, is used as the basic scheme for range-based localization. First, based on the characterization of random link loss in wireless sensor networks with a Bernoulli random variable, a distributed iterative localization algorithm is proposed. And then, the global convergence of the proposed localization algorithm which ensures accurate localization is theoretically proved by using the convergence of sub-stochastic matrices’ product. Finally, numerical examples are conducted to illustrate the effectiveness of the proposed localization algorithm.

Improving TCP performance over a common IoT scenario using the Early Window Tailoring method

The Internet of Things (IoT) is already a reality in homes, transforming the home network into a complex composition of different equipment where each one has its own attributes in terms of TCP protocol variants, transmission speed, reliability and delay. In home network scenarios where IoT devices are used, it is common to have a 802.11 environment with several devices sharing the same Access Point (AP). When TCP is used in this environment its performance is affected by many things, such as wireless link losses, queue saturation on access points, and fairness. To improve the TCP performance in these scenarios, this paper presents a new version of the Early Window Tailoring (EWT) approach. The EWT-IoT do not require any modification in the TCP, and it does not require that all routers in the path use the same Active Queue Management (AQM), the use in the AP is sufficient. To evaluate its performance, comparison tests against drop-tail, RED, ARED and EWA were performed. The EWT-IoT proved to be effective in congestion control, achieving greater performance than the other approaches, reducing the transfer time, having a superior goodput, maintaining a satisfactory fairness, and presenting no losses. Also, the EWT-IoT allowed the existence of a number of flows on average 65.2% better than its best competitor and 71.3% better when no AQM scheme was used.

Quantum-limited optical time transfer for future geosynchronous links.

The combination of optical time transfer and optical clocks opens up the possibility of large-scale free-space networks that connect both ground-based optical clocks and future space-based optical clocks. Such networks promise better tests of general relativity1-3, dark-matter searches4 and gravitational-wave detection5. The ability to connect optical clocks to a distant satellite could enable space-based very long baseline interferometry6,7, advanced satellite navigation8, clock-based geodesy2,9,10 and thousandfold improvements in intercontinental time dissemination11,12. Thus far, only optical clocks have pushed towards quantum-limited performance13. By contrast, optical time transfer has not operated at the analogous quantum limit set by the number of received photons. Here we demonstrate time transfer with near quantum-limited acquisition and timing at 10,000 times lower received power than previous approaches14-24. Over 300 km between mountaintops in Hawaii with launched powers as low as 40 µW, distant sites are synchronized to 320 attoseconds. This nearly quantum-limited operation is critical for long-distance free-space links in which photons are few and amplification costly: at 4.0 mW transmit power, this approach can support 102 dB link loss, more than sufficient for future time transfer to geosynchronous orbits.

Real-Time 100 Gb/s PAM-4 for Access Links With up to 34 dB Power Budget

The growing demand for broadband access networks keeps motivating research for higher capacity in both wired and wireless access networks. Recently, the recommendation for 50G-PON with conventional NRZ modulation has been published. Bidirectional point-to-point access networks, also known as BiDi, used in mobile xHaul, are standardized up to 50 Gb/s with PAM-4 as modulation format. The evolution in view of a next generation 6G wireless encourages research towards higher bitrates for fronthaul systems. Hence, there is interest for having single channel BiDi links with a bitrate of at least 100 Gb/s. In this paper we experimentally evaluate four possible IMDD transceiver schemes suitable for optical access applications in the O-Band that can cover BiDi link losses up to a bitrate of 100 Gb/s using PAM-4. We employ an EML with either a 25G-based APD or an optically preamplified p-i-n photodiode (PD) with low-complexity FFE equalization and achieve a real-time power budget of 23.7 dB, just above BiDi B- loss class. By adding an optical booster, we demonstrate up to 34 dB power budget, exceeding with enough margin the highest BiDi class B loss of 25 dB.

Path loss modeling and performance evaluation of double IRSs-aided wireless communication systems based on spatial scattering channel model

Intelligent reflecting surface (IRS) is a key enabling technology to reshape the electromagnetic propagation environment and enhance the communication performance. Current single IRS-aided or multiple distributed IRSs-aided wireless communication systems leave inter-IRSs collaboration out of consideration, and as a result, the system performance may be severely restricted. For cooperative double IRSs-aided wireless communication systems, dyadic backscatter channel model is widely used in the performance analysis and optimization. However, the impact of factors such as the size and gain of IRS elements is omitted. As a result, the performance quantification and evaluation are inaccurate. In order to avoid the above limitations, spatial scattering channel model is leveraged to quantify the path loss of the double reflection link in typical application scenarios of double IRSs-aided wireless communication systems. When the near-field condition is satisfied, the electromagnetic wave signal transmitted between IRSs is a spherical wave, which leads to high-rank channel and a lower signal to noise ratio. This paper considers the rank-1 inter-IRSs equivalent channel and derives the closed-form received signal power which reveals its relationship with the deployment of IRSs and the physical and electromagnetic properties of IRSs. Taking the impact of near/far-field effects of IRS on signal propagation further into consideration, the network configurations under which double cooperative IRSs can enhance the system performance are recognized. Simulation results show that whether double IRSs should be selected to assist in the communication between the transmitter and the receiver depends on practical network configurations, and the same number of elements should be assigned to the two IRSs to maximize the system performance if they are adopted.

Dynamic Network Topology Portrait for Digital Twin Optical Network

Digital twin (DT) as one promising technology has been introduced in optical networks, whose role is to achieve interactive functions and intelligent control by building a bridge between physical space and digital space. In this paper, a multifactor-associated network topology portrait (NTP) scheme is proposed to draw a dynamic, real-time, and comprehensive topology representation for DT optical network (DTON). Multiple parameters from nodes and links are jointly evaluated, including link distance, link loss, optical signal-to-noise ratio, bandwidth utilization rate, load capacity, node failure rate, and link failure rate, involving both network layer and physical layer. Based on the NTP, the performance of dynamic routing computation combined with six different routing algorithms is studied, Here, the time for routing computation is sacrificed a little bit in exchange for significant improvements in outage probability, outage latency, and the number of service requests.

Link cascade failure in directed networks with higher-order structures

In the field of complex networks, cascade failure has been widely studied due to its ubiquity and profound impact. While in recent years, the conceptualization of “higher-order structures” has brought the research of complex networks to a new stage. However, the effect of higher-order structures on cascade failure dynamics remains to be understood. In this study, we consider a link cascade failure mechanism in combination with higher-order structures. In the process of link cascade failure, we find that the network robustness would be affected by the nodes' ability to withstand link loss and the proportion of higher-order structures, corresponding to the changes in the critical point and the type of phase transition. These findings have been examined in the modeled and real directed networks. Interestingly, in empirical networks, we find that for networks with larger average shortest paths (e.g. US Airlines), the impact of higher-order structures on network robustness is more prominent.

Demonstration of 12.5 Mslot/s 32-PPM Underwater Wireless Optical Communication System with 0.34 Photons/Bit Receiver Sensitivity

High-capacity, long-distance underwater wireless optical communication (UWOC) technology is an important component in building fast, flexible underwater sensing networks. Underwater communication with light as a carrier has a large communication capacity, but channel loss induced by light attenuation and scattering largely limits the underwater wireless optical communication distance. To improve the communication distance, a low-power 450 nm blue continuous wave (CW) laser diode (LD)-based UWOC system was proposed and experimentally demonstrated. A communication link was designed and constructed with a BER of 3.6 × 10−3 in a total link loss of 80.72 dB in c = 0.51 m−1 water with a scintillation index (S.I.) equal to 0.02 by combining with 32-pulse-position modulation (32-PPM) at a bandwidth of 12.5 MHz and single photon counting reception techniques. The allowable underwater communication distance in Jerlov II (c = 0.528 m−1) water was estimated to be 35.64 m. The attenuation lengths were 18.82, which were equal at link distances of 855.36 m in Jerlov I (c = 0.022 m−1) water. A receiving sensitivity of 0.34 photons/bit was achieved. To our knowledge, this is the lowest receiving sensitivity ever reported under 0.1 dB of signal-to-noise ratio (SNR) in the field of UWOC.

Consensus-Based Robust Filtering Over Sensor Networks With Weighted and Unweighted Topologies and Communication Delays

In this article, a consensus-based robust filter is proposed for sensor networks with weighted and unweighted topologies, and communication delays. The system is considered to be linear time-varying (LTV) with bounded uncertainties. In order to achieve the desired filter, first, a robust optimization problem is defined based on the consensus protocol for unweighted topologies. The consensus protocol ensures an agreement between the estimates of all sensors. By solving this problem, the proposed consensus-based robust filter is obtained and its algorithm is presented. Then, to increase the applicability of the filter, another optimization problem for weighted topologies is introduced. Next, due to the impact and high importance of communication delays in sensor networks, by considering the time-varying delays in consensus protocols, new optimization problems are solved again to achieve a suitable filter. One of the most significant features of the proposed consensus-based robust filters is that the loss of a large part of the network links does not pull down the filtering performance. Finally, in the simulation section, the robust performance and efficiency of the proposed consensus-based robust filters have been investigated for weighted and unweighted networks in the presence of time-varying delays and loss of communication links.

Les unités de soins spécialisés Alzheimer : une seconde peau psychique ?

ContextBased on our clinical experience in gerontopsychiatry and on psychoanalytical concepts, we wish to discuss the therapeutic effects of specialized Alzheimer care units on the subjects they accommodate. ObjectivesIn the context of a public health problem, these units have developed particular characteristics and aims, in order to attempt to respond. Their therapeutic role is not self-evident and it can be effective only under certain conditions. Through this reflection, we attempt to identify the operators of the processes of changes in psychic functioning and to understand which conditions allow them to be deployed. When these conditions are absent, these units can crystallize certain excesses, whether at the institutional or the individual level. MethodThis reflexion is based on the concept of the « Moi-Peau » (the Self-Skin or the Skin-Self), here used to clarify the functions of symbolization and interface, but also their toxic effects when the counter-transference invades the relationship. When these special care units function as a transitional area, they can support the psychological dynamics of symbolization and exchanges in demented subjects, and can bring about therapeutic effects on behavioral disorders. When this transitionality is not effective, these units become a place of confinement where the balance between life and death is lost, which can lead to the intensification of the dementia process and the loss of relational links. ResultsThis reflection opens up avenues of research, both qualitative and quantitative, on the functioning of these units, which are bound to develop in response to the increasing number of people suffering from dementia ias the population ages. ConclusionIt's the way in which these units are invested that allows them to have their therapeutic character. Therefore, it's necessary to develop knowledge about how Alzheimer units are investing in order to adjust care strategies to the characteristics of this population and to support people with dementia and behavioral problems.

Crucial problems of the organization of biosphere reserves in Azerbaijan


 
 
 The environment is an important issue even when society is faced with economic crises, wars, and unending social problems. It matters because Earth is the only home that humans have, and it provides air, food, and other needs. Economic development, demographic growth, increase in consumption due to increase in the income level of the population, climate changes and other reasons have resulted in an increase in the negative impact on the environment. Pollution of water basins with waste water, release of harmful gases into the atmosphere, reduction of biodiversity, soil erosion and salinization, deficiencies in the field of waste management are considered among the existing ecological problems. The paper deals with specific features of the organization of biosphere reserves in Azerbaijan. A significant challenge of our time is conserving biological diversity while maintaining economic development and cultural values. The United Nations Educational, Scientific and Cultural Organization has established biosphere reserves within its Man and the Biosphere program as a model means for accomplishing this very challenge. The loss of cultural links and traditional knowledge has also been significant. Nevertheless, it remains a highly biodiversity area. Political barriers and institutional blockages will have to be removed to ensure this reserve fulfills its role as a model region for international collaboration and capacity building. These insights drawn from the Eastern Carpathians Biosphere Reserve demonstrate that biosphere reserves are indeed learning sites for sustainable development and that this case is exemplary in illustrating the challenges, but more importantly, the opportunities that arise when ensuring parallel care and respect for people and ecosystems through the model of trans boundary protected areas around the world.
 
 

Aerial Edge Computing on Orbit: A Task Offloading and Allocation Scheme

As the communication mode with the greatest attention and global network coverage, the Low Earth Orbit (LEO) satellite network has the characteristics of low propagation delay, low link loss and handheld terminal. However, with the increasing requirements of user terminals for network latency and bandwidth, the traditional central cloud computing mode no longer has advantages. Therefore, borrowing from the idea of edge computing in terrestrial networks, Orbital Edge Computing (OEC) technology deploys Multi-access Edge Computing (MEC) servers on LEO satellite constellations to meet the growing demand for real-time and reliability of various applications. Based on the above motivations, this paper proposes an OEC Task Allocation (OEC-TA) algorithm based on the greedy strategy in LEO satellite networks for the Walker Delta satellite constellation, which fully utilizes satellite computing resources to provide services to ground users. Then, we analyze the performance of our proposed algorithm in terms of computational cost. Finally, experimental results show that OEC-TA is better than DEC (Double Edge Computing) and random allocation model on average delay and energy consumption reduction. Compared with DEC, our OEC-TA can reduce the average delay and energy consumption up to 10% and 16.5%, respectively.

Geographic Drone-based Route Optimization Approach for Emergency Area Ad-Hoc Network

Wireless sensor Mobile ad hoc networks have excellent potential in moving and monitoring disaster area networks on real-time basis. The recent challenges faced in Mobile Ad Hoc Networks (MANETs) include scalability, localization, heterogeneous network, self-organization, and self-sufficient operation. In this background, the current study focuses on specially-designed communication link establishment for high connection stability of wireless mobile sensor networks, especially in disaster area network. Existing protocols focus on location-dependent communications and use networks based on typically-used Internet Protocol (IP) architecture. However, IP-based communications have a few limitations such as inefficient bandwidth utilization, high processing, less transfer speeds, and excessive memory intake. To overcome these challenges, the number of neighbors (Node Density) is minimized and high Mobility Nodes (Node Speed) are avoided. The proposed Geographic Drone Based Route Optimization (GDRO) method reduces the entire overhead to a considerable level in an efficient manner and significantly improves the overall performance by identifying the disaster region. This drone communicates with anchor node periodically and shares the information to it so as to introduce a drone-based disaster network in an area. Geographic routing is a promising approach to enhance the routing efficiency in MANET. This algorithm helps in reaching the anchor (target) node with the help of Geographical Graph-Based Mapping (GGM). Global Positioning System (GPS) is enabled on mobile network of the anchor node which regularly broadcasts its location information that helps in finding the location. In first step, the node searches for local and remote anticipated Expected Transmission Count (ETX), thereby calculating the estimated distance. Received Signal Strength Indicator (RSSI) results are stored in the local memory of the node. Then, the node calculates the least remote anticipated ETX, Link Loss Rate, and information to the new location. Freeway Heuristic algorithm improves the data speed, efficiency and determines the path and optimization problem. In comparison with other models, the proposed method yielded an efficient communication, increased the throughput, and reduced the end-to-end delay, energy consumption and packet loss performance in disaster area networks.

Effect of Rain Attenuation on Millimeter Wave over Polarization

Millimeter wave has been used in radar applications for a long time, and is increasingly used in new fields, among which high data rate telecommunications is the most prominent. Short wavelength and unique propagation characteristics provide challenges and opportunities for design engineers working in these fields. Millimeter wave has become an indispensable part of 5G mobile communication field due to its excellent spectrum characteristics. In order to help the development of millimeter wave equipment, this paper mainly studies the millimeter wave rain attenuation phenomenon through the combination of theory and simulation. The effects of rainfall rate and polarization mode on millimeter wave propagation attenuation are compared and summarized. In addition, the total attenuation of millimeter wave communication path under different polarization rainfall characteristics is compared. Finally, the total loss of different frequency millimeter wave rainfall links is compared and analyzed. It provides a theoretical basis for the follow-up design and practical application of millimeter wave communication system.

Intelligence Reflecting Surface-Aided Integrated Data and Energy Networking Coexisting D2D Communications

In this paper, we consider an integrated data and energy network and D2D communication coexistence (DED2D) system. The DED2D system allows a base station (BS) to transfer data to information-demanded users (IUs) and energy to energy-demanded users (EUs), i.e., using a time-fraction-based information and energy transfer (TFIET) scheme. Furthermore, the DED2D system enables D2D communications to share spectrum with the BS. Therefore, the DED2D system addresses the growth of energy and spectrum demands of the next generation networks. However, the interference caused by the D2D communications and propagation loss of wireless links can significantly degrade the data throughput of IUs. To deal with the issues, we propose to deploy an intelligent reflecting surface (IRS) in the DED2D system. Then, we formulate an optimization problem that aims to optimize the information beamformer for the IUs, energy beamformer for EUs, time fractions of the TFIET, transmit power of D2D transmitters, and reflection coefficients of the IRS to maximize IUs’ worse throughput while satisfying the harvested energy requirement of EUs and D2D rate threshold. The max-min throughput optimization problem is computationally intractable, and we develop an alternating descent algorithm to resolve it with low computational complexity. The simulation results demonstrate the effectiveness of the proposed algorithm.

915 MHz Miniaturized Loop Conformal Antenna for Capsule Endoscope

High-performance miniaturized antennas are one of the goals that have been pursued in the design of wireless communication systems for implantable medical devices. In this article, a 915 MHz novel-shape loop antenna conforming to the inner wall of the capsule is developed by comprehensively adopting meander and symmetrical structure patch, folding technique, and vector current reversal technique. Through electromagnetic simulation, testing, and experimentation, the antenna shows good characteristics such as small size, ultra-wideband, circular polarization, strong robustness, and safety. Specific performances include the following: 1) the size of the developed miniaturized loop conformal antenna is only 30.5 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 4.6 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 0.05 mm and the maximum gain is −21.5 dBi at 915 MHz, which solves the problem of low gain due to the small antenna radiation area; 2) the antenna has a 4.5 GHz ultra-wideband impedance matching bandwidth ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\vert S_{11}\vert &lt; -10$ </tex-math></inline-formula> dB) from 0.5 to 5 GHz. Even if the parameters such as the implantation depth and the thickness of the capsule shell change, or there exists a wireless power transfer system, the antenna can still cover the required frequency band with strong robustness; and 3) the specific absorption rate (SAR) of human tissues radiated by the antenna is far lower than the safety limit in IEEE standards and ICNIRP guidelines. The experimental platform using pork to simulate human tissues was built for antenna performance testing and communication testing. The measurement results verified the good resonance performance, radiation characteristics, and omnidirectionality of the developed antenna. The antenna link loss model is also given, which has been used in wireless communication and localization.

Bi-layer optimal secondary frequency control approach for energy storage clusters considering wind power uncertainty

Increasing penetration of wind power with intermittency and variability threatens the stability of the power system frequency. The fast response capability of the energy storage system (ESS) makes it an effective measure to improve frequency regulation performance. However, designing an optimal control for numerous energy storage units (ESUs) with different power and energy characteristics is challenging. To solve the dilemma that the distributed control methods cannot achieve optimality over time horizons while the centralized optimization methods would cause high computational burdens, a bi-layer optimal control approach is proposed in this study. In the upper layer, a multi-area secondary frequency control (SFC) problem is established to determine control policies for ESS clusters under continuous wind power fluctuations and is solved by the Itô theory-based stochastic optimization (ITB-SO) method with high computational efficiency in a rolling-horizon manner. In the lower layer, the power output of ESUs is dispatched and coordinated using the distributed algorithm (DA) method via communication networks, considering different characteristics and the current state-of-charge (SoC) levels. Simulation studies carried out in a dual-region test system evidence the improvement of system frequency stability by compensating for rapid wind power fluctuations immediately via ESSs. The results show that the proposed ITB-SO method without scenario generation is suitable for real-time SFC for the ESS. The effectiveness of the DA method and its robustness in encountering loss of communication links are also verified.

Distributed Economic Dispatch Control Method with Frequency Regulator for Smart Grid under Time-Varying Directed Topology

The paper studies a new distributed control method to solve the economic dispatch problem (EDP) under directed topology based on consensus protocol. Electrical equipment is closely related to frequency, and the frequency of each generator varies independently during operation. Therefore, it hinders the realization of economic dispatch. To solve the problem, we combine a frequency regulator with a consensus protocol, which eliminates the effect of frequency variation on the designed consensus algorithm. Meanwhile, considering the problem of excessive communication cost and low computational efficiency in large-scale power systems, an event-triggered mechanism is introduced into the designed algorithm. Furthermore, in order to overcome the unexpected loss of communication links, the time-varying topology mechanism is employed to develop the distributed economic dispatch (DED) algorithm to improve the robustness. Then, the stability of the above algorithm is proved by graph theory and convergence analysis. Finally, several simulations illustrate that our proposed methods are effective.