Average Fade Research Articles

Envelope Level Crossing Rate and Average Fade Duration of Low-Altitude UAV-to-UAV Channels

Envelope Level Crossing Rate and Average Fade Duration of Low-Altitude UAV-to-UAV Channels

Tellurium doped sulfurized polyacrylonitrile nanoflower for high-energy-density, long-lifespan sodium-sulfur batteries

Sodium-sulfur (Na−S) batteries are promising energy storage devices for large-scale applications due to their high-energy-density and abundant material reserve. However, the practical implementation of room temperature (RT) Na−S batteries faces challenges, including low-energy-density and limited lifespan, particularly attributed to the properties of sulfurized polyacrylonitrile (SPAN). In this study, we address these challenges by introducing tellurium doping into SPAN nanoflowers, enhancing their performance for Na−S batteries. The resulting material exhibits high sulfur loading as well as superior electron and ion transport properties, leading to enhanced redox kinetics and improved battery performance. The tellurium-doped SPAN nanoflower electrode delivers an exceptional composite capacity of 700 mAh g−1 at 0.1 C and demonstrates stable cycling over 2400 cycles with minimal capacity fade (0.01 % average fading rate). Even under challenging conditions (24.0 mg cm−2, E/S=5 mg μLS−1, N/P=2.1), the Na−S battery achieves a high areal capacity of 16.1 mAh cm−2, resulting in an impressive energy density of 340.9 Wh kg–1 based on cathode and anode. This work presents a promising approach to designing high-energy-density, long-lifespan RT Na−S batteries, with potential applications for other metal-sulfur battery systems.

Performance implications of channel aware cooperative probing-GBN ARQ in the context of wireless body area networks

The advent of Wireless Body Area Networks (WBAN) in patient care has revolutionized the healthcare sector as patients can now be monitored continuously in real-time and as well remotely. Despite its significant advantages, WBAN encounters a notable challenge in the fading aspect, which undermines its effectiveness. Improving WBAN efficiency involves tackling signal fading, which is crucial. Cooperative communication offers a promising solution by introducing spatial diversity to counteract fading effects. We propose a scheme that uses cooperative communication and the Probing-Go Back N Automatic Repeat Request (P-GBN ARQ) technique to reduce the fading effect. The proposed method uses feedback to predict the channel's current state, and the probing interval is determined by the received signal's Average Fading Duration (AFD). The proposed scheme's performance is also assessed extensively through simulations employing various metrics. The results demonstrate a considerable improvement in throughput performance with the inclusion of knowledge about channel fading. The Bit Error Rate (BER) execution is compared with Selection Combiner (SC) and conventional Maximal Ratio Combining (MRC). At 10−3, the cooperative method achieves it at 13 dB SNR, whereas the direct approach reaches it at 24 dB SNR, requiring an additional 11 dB. The proposed approach minimizes BER, enhancing throughput and reliability in WBAN.

MDE and LLM Synergy for Network Experimentation: Case Analysis of Wireless System Performance in Beaulieu-Xie Fading and κ-µ Co-Channel Interference Environment with Diversity Combining.

Channel modeling is a first step towards the successful projecting of any wireless communication system. Hence, in this paper, we analyze the performance at the output of a multi-branch selection combining (SC) diversity receiver in a wireless environment that has been distracted by fading and co-channel interference (CCI), whereby the fading is modelled by newer Beaulieu-Xie (BX) distribution, and the CCI is modelled by the κ-µ distribution. The BX distribution provides the ability to include in consideration any number of line-of-sight (LOS) useful signal components and non-LOS (NLOS) useful signal components. This distribution contains characteristics of some other fading models thanks to its flexible fading parameters, which also applies to the κ-µ distribution. We derived here the expressions for the probability density function (PDF) and cumulative distribution function (CDF) for the output signal-to-co-channel interference ratio (SIR). After that, other performances are obtained, namely: outage probability (Pout), channel capacity (CC), moment-generating function (MGF), average bit error probability (ABEP), level crossing rate (LCR), and average fade duration (AFD). Numerical results are presented in several graphs versus the SIR for different values of fading and CCI parameters, as well as the number of input branches in the SC receiver. Then, the impact of parameters on all performance is checked. From our numerical results, it is possible to directly obtain the performance for all derived and displayed quantities for cases of previously known distributions of fading and CCI by inserting the appropriate parameter values. In the second part of the paper, a workflow for automated network experimentation relying on the synergy of Large Language Models (LLMs) and model-driven engineering (MDE) is presented, while the previously derived expressions are used for evaluation. Due to the aforementioned, the biggest value of the obtained results is the applicability to the cases of a large number of other distributions for fading and CCI by replacing the corresponding parameters in the formulas for the respective performances.

The effectiveness of topical gel formulation extract Centella asiatica and Curcuma domestica to fading striae gravidarum

Background: The incidence of striae gravidarum in Indonesia is 95%, and 79.7% are primigravida. Striae gravidarum is not a direct physical health risk but is associated with body image and decreased self-confidence. Curcuma domestica contains curcumin and vitamin C, which can stimulate the synthesis of type IV collagen. In contrast, the Centella asiatica plant contains triterpenoids and saponins, which can stimulate the synthesis of type I collagen, which helps regenerate skin cells and improve skin elasticity. However, it is necessary to see the effectiveness of the two herbs, Centella asiatica and Curcuma domestica, in fading striae gravidarum. Purpose: To prove the effectiveness of topical gel formulation extract Centella asiatica and Curcuma domestica for fading of striae gravidarum.Methods: This is a quasi-experimental study with a pretest-posttest control group design. The sample consisted of 32 primigravida pregnant women divided into two groups: the intervention group was given a combination of Curcuma domestica and Centella asiatica gel at a dose of 5 mg twice a day for 14 days, and the control group was given a mineral oil gel at a quantity of 5 mg twice a day for 14 days—measurement of striae gravidarum using Davey score. The statistical test used the Friedman and Wilcoxon test.Results: The average fading of striae gravidarum in the intervention group was more significant than in the control group, 11.44±4.131 to 4±3.033 vs.12.19±5.788 to 8.56±4.320 treatment on the 14th day. The analysis results showed that the topical gel formulation of Centella asiatica and Curcuma domestica was more effective in fading striae gravidarum than the placebo gel (p<0.001).Conclusion: Administering topical gel containing 12% Centella asiatica extract and a 10% Curcuma domestica dose of 5 mg twice a day for 14 days affected the fading of striae gravidarum.

Sandwich-type CoSe2-CNWs@NG as host for lithium-sulfur batteries with high sulfur loading, ultrahigh rate, and long lifespan

While lithium-sulfur batteries (LSBs) have tremendous potential in capacity and energy, their application in practice is limited by short cycle life, slow reaction kinetics, and underutilization of sulfur. To tackle these challenges, we have developed a multifunctional host consisting of sandwich-type CoSe2-CNWs@NG that were hydrothermally synthesized through self-assembly of CoSe2-embedded carbon nanowires (CoSe2-CNWs) with N-doped graphene (NG). Through the implementation of CoSe2-CNWs@NG as a host material, active sulfur can be effectively intercalated within the interlayer spaces of neighboring NG layers. The extensive contact area between sulfur and NG sheets facilitates rapid electron transfer, thereby maximizing sulfur utilization. N-doped graphene and polar CoSe2 provide sufficient chemisorption sites for polysulfides, while the catalytic activity of CoSe2 promotes polysulfide conversion. In addition to building a good conductivity structure for fast carrier transport and electrolyte diffusion, the sandwich structure of CoSe2-CNWs@NG physically restricts polysulfides and buffers substantial sulfur volume changes during cycling. As a result, the CoSe2-CNWs@NG/S cathode possessing high-load sulfur capacity (4.06 mg cm−2) exhibits superior cell performance at an ultrahigh rate as well as low E/S ratio. After 1000 cycles at 10 C, it achieves a remarkable reversible capacity of 314.4 mAh g−1 with an impressively low average fading rate of 0.023 % per cycle. Even at a low E/S ratio of 5 μL mg−1, the cathode exhibits remarkable performance, retaining a reversible capacity of 628.2 mAh g−1 after 150 cycles at the rate of 1 C.

Sandwich-Structured Anode Enables High Stability and Enhanced Zinc Utilization for Aqueous Zn-Ion Batteries

Constructing a current collector is a promising approach to modifying the zinc anode. However, most collectors exhibit top zinc deposition patterns, leading to unsatisfactory zinc utilization and instability. To address this issue, we have developed a new sandwich deposition approach in which a boron nitride layer (BN layer) is applied onto Cu foils as the current collector, which allows us to achieve the sandwich-structured anode (BN-Zn-Cu). Through experimental characterization and theoretical calculations, the deposition mechanisms of Zn2+ have been explored and verified. The insulating BN layer, the upper layer of the anode, acts as the protective barrier of deposited zinc and accelerates the transmission of zinc ions. The zincophilic Cu substrate, the bottom layer of the anode, promotes Zn deposition without dendrites. Under the synergistic effect of the BN layer and substrate, the sandwich-structured anode enables superior reversibility with 99.49 % coulombic efficiency over 700 cycles and realizes 66.7% zinc utilization at 4 mAh cm−2. Moreover, the assembled BN-Zn-Cu||CNT/MnO2 cells display high stability with an average fading of 0.06% per cycle for 600 cycles. Our work verifies the feasibility of sandwich-structured anodes in enhancing the performance of aqueous zinc-ion batteries, providing an innovative idea for the structural design of metal anodes.

Experimental study on low-altitude UAV-to-ground propagation characteristics in campus environment

In recent years, unmanned aerial vehicle (UAV)-to-ground wireless channels have become focused areas. Thus a better understanding of UAV-to-ground wireless channel characterizations is critical. The large-scale fading characterization is widely analyzed in many research works. Nevertheless, the small-scale fading characterization of low-altitude UAV-to-ground propagation has not been fully modeled. In this work, the close-in (CI) free space and floating-intercept (FI) path loss models are implemented to characterize large-scale fading. The large-scale parameters, i.e., path loss exponent (PLE), shadow fading standard deviation (STD), and shadow fading correlation coefficient, are carefully extracted, analyzed, and compared. Regarding small-scale fading, Akaike’s Information Criteria (AIC) is used to find the most suitable fading distribution. In addition, fade depth (FD), level crossing rate (LCR), and average fade duration (AFD) are also calculated. The quantitative results and comparisons show a noticeable difference with ground propagation. The parameterized models are helpful for further understanding and deployment of UAV-to-ground wireless communication systems.

A three‐dimensional two‐hemisphere model for unmanned aerial vehicle multiple‐input multiple‐output channels

AbstractThe application of unmanned aerial vehicles (UAVs) has recently attracted considerable interest in various areas. A three‐dimensional multiple‐input multiple‐output concentric two‐hemisphere model is proposed to characterize the scattering environment around a vehicle in an urban UAV‐to‐vehicle communication scenario. Multipath components of the model consisted of line‐of‐sight and single‐bounced components. This study focused on the key parameters that determine the scatterer distribution. A time‐variant process was used to analyze the nonstationarity of the proposed model. Vital statistical properties, such as the space–time–frequency correlation function, Doppler power spectral density, level‐crossing rate, average fade duration, and channel capacity, were derived and analyzed. The results indicated that with an increase in the maximum scatter radius, the time correlation and level‐crossing rate decreased, the frequency correlation function had a faster downward trend, and average fade duration increased. In addition, with the increase of concentration parameter, the time correlation, space correlation, and level‐crossing rate increased, average fade duration decreased, and Doppler power spectral density became flatter. The proposed model was compared with current geometry‐based stochastic models (GBSMs) and showed good consistency. In addition, we verified the nonstationarity in the temporal and spatial domains of the proposed model. These conclusions can be used as references in the design of more reasonable communication systems.

Measurements and Characteristics Analysis of 6G Ultra-Massive MIMO Wireless Channels With Different Antenna Configurations and Scenarios

In this paper, ultra-massive multiple-input multiple-output (MIMO) channel measurements at 5.3 GHz are conducted, including different antenna array configurations and different measurement scenarios. The antenna array configurations include uniform linear array (ULA) and distributed uniform linear array (DULA). The measurement scenarios include single-user fixed-to-fixed (F2F), multi-user F2F, and single-user fixed-to-mobile (F2M) measurement scenarios. The statistical properties of ultra-massive MIMO channels are studied, including delay power spectral density (DPSD), space cross-correlation function (SCCF), angle cross-correlation function (ACCF), frequency correlation function (FCF), root mean square (RMS) delay spread (DS), RMS angle spread (AS), singular value spread (SVS), scalar product (SP), level crossing rate (LCR), average fading duration (AFD), Doppler power spectral density (PSD), etc. The specific ultra-massive MIMO channel characteristics are investigated and validated by channel measurements, including spatial non-stationarity, spherical wavefront behavior, channel hardening, and sparse properties in the angle domain. In addition, channel capacities are investigated. The channel measurement results will be a great importance for ultra-massive MIMO communication system deployments.

3D geometry‐based UAV to vehicle multiple‐input multiple‐output channel model incorporating Unmanned aerial vehicle heaving motion

AbstractUnmanned aerial vehicles (UAVs) play a vital role in the beyond fifth‐generation (B5G) and sixth‐generation (6G) wireless communication scenarios. This paper proposes a non‐stationary three‐dimensional (3D) geometry‐based multiple‐input multiple‐output channel model for UAV to vehicle (U2V) communications considering UAV heaving motion. The proposed model incorporates the effects of UAV heaving along with the rotation, acceleration, and 3D velocity variation for matching the realistic U2V communication scenarios. The computation methods for time variant channel parameters such as Doppler frequencies, angle of arrival, and angle of departure are given and analysed. The theoretical and statistical properties, including spatial temporal correlation function, TCF, level crossing rate, average fade duration, and Doppler power spectral density are derived and analysed aiming to evaluate the proposed model. Simulation results show that the output statistical characteristics agree with the hypothetical and simulated outcomes, which shows the validity of both the channel model and theoretical derivations.The cover image is based on the Research Article 3D geometry‐based UAV to vehicle multiple‐input multiple‐output channel model incorporating Unmanned aerial vehicle heaving motion by Naeem Ahmed et al., https://doi.org/10.1049/mia2.12393

Channel Modeling for UAV-to-Ground Communications With Posture Variation and Fuselage Scattering Effect

Unmanned aerial vehicle (UAV)-to-ground (U2G) channel models play a pivotal role in reliable communications between UAV and ground terminal. This paper proposes a three-dimensional (3D) non-stationary hybrid model including large-scale and small-scale fading for U2G multiple-input-multiple-output (MIMO) channels. Distinctive channel characteristics under U2G scenarios, i.e., 3D trajectory and posture of UAV, fuselage scattering effect (FSE), and posture variation fading (PVF) are incorporated into the proposed model. The channel parameters, i.e., path loss (PL), shadow fading (SF), path delay, and path angle, are generated incorporating machine learning (ML) and ray tracing (RT) techniques to capture the structure-related characteristics. In order to guarantee the physical continuity of channel parameters such as Doppler phase and path power, the time evolution methods of inter- and intra- stationary intervals are proposed. Key statistical properties, including temporal auto-correction function (ACF), power delay profile (PDP), level crossing rate (LCR), average fading duration (AFD), and stationary interval (SI), are analyzed with the impact of the change of fuselage and posture variation. It is demonstrated that both posture variation and fuselage scattering have crucial effects on channel characteristics. The validity and practicability of the proposed model are verified by comparing the simulation results with the measured ones.

Poly(Vinylidene Fluoride-co-Hexafluoropropylene) Films Filled in Iron Nanoparticles for Infrared Shielding Applications.

In order to use the infrared (IR) radiation shielding materials, they should take a form of thin film coatings deposited on glass/polymer substrates or be used as fillers of glass/polymer. The first approach usually suffers from several technological problems. Therefore, the second strategy gains more and more attention. Taking into account this trend, this work presents the usage of iron nanoparticles (Fe NPs) embedded into the poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) films as the shielding material in near-infrared (NIR) and mid-infrared (MIR) region. The performed investigations show that the transmittance of copolymer films decreases with increasing content of the Fe NPs inside them. It is found that the average fade of IR transmittance for 1, 2.5, 5, 10, and 50mg of Fe NPs is about 13%, 24%, 31%, 77%, and 98%, respectively. Moreover, it is observed that the PVDF-HFP films filled in the Fe NPs almost does not reflect the NIR and MIR radiation. Hence, the IR shielding properties of the PVDF-HFP films can be effectively tuned by the addition of proper amount of the Fe NPs. This, in turn, shows that the PVDF-HFP films filled in the Fe NPs constitute a great option for IR antireflective and shielding applications.

On the second order statistics of the ratio of two Fisher-Snedecor random variables and its application to interference limited communications

The paper investigates the higher order statistics of the ratio of two Fisher-Snedecor F (FS-F) random variables (RVs) and its application to wireless communications in the presence of co-channel interference. Namely, the work provides novel expressions for probability density function (PDF), cumulative density function (CDF), level crossing rate (LCR) and average fade duration (AFD) of the ratio of two FS-F RVs. Numerical examples of the analytically derived statistical measures in terms of FS-F multi-path and shadowing parameters are shown and examined. Moreover, the impact of the number of interferes on the considered measures are further presented and examined.

Caching in Narrow-Band Burst-Error Channels via Meta Self-Supervision Learning

We consider a coordinated small-cell network in narrow-band deep fading channels, where the transmissions from small base-stations (SBSs) to users usually encounter burst errors. Each SBS has limited cache-capacity via which partial contents can be cached to avoid being fetched from remote cloud and hence reduce the transmission delay. However, due to deep fading, the content transmission may occur numerous burst errors. To solve this problem, in this letter, a meta-based self-supervision learning method is introduced to find the optimal cache policy for minimizing the burst errors. In contrast to the traditional methods, the proposed one has better performance and learning efficiency. More particularly, the proposed can determine much proper cache policy by just training with a few samples of average fading duration of each channel. We demonstrate the effectiveness of the proposed method by numerical simulations which indicate that the proposed meta-learning method is superior to common existing methods in combat of the burst-error problem regarding convergence time and accuracy.

A New Vertical Handover Prediction Method for Heterogeneous Wireless Networks

Long Term Evolution (LTE) is the fourth generation (4G) cellular network technology that provides improved performance that related to data rate, coverage and capacity compared to earlier cellular systems. The addition of many small cells in a heterogeneous network configuration provides a means to enhance capacity through extreme frequency reuse. The heterogeneous environment of different network technologies can provide high data rate and enhance multimedia services, but it is challenging to provide optimized handover (HO). In this paper, a new method is proposed to select the optimal network from available networks to which a UE may be handed over to achieve better QoS performance. The aggregation of multiple criteria for calculation of overall ranking of networks is obtained by Analytical Hierarchy Process (AHP) [1] and is combined with the history of previously visited cells and regression analysis of the Layer 1 (L1) and Layer 3 (L3) filtered Received Signal Strength (RSS) data for prediction of future values. The AHP is used to calculate the weights for the system attributes and to rank the available networks based on multiple criteria Multiple Attribute Decision Making (MADM). The sequence of visited cells is used in target network selection as it reduces frequent handover. The sequence of visited cells would be modeled as a Markov Chain. To assess RSS, beside L1, L3 filtering RSS prediction and smoothing is used to predict future signal samples to hasten the process of HO. RSS forecasting is used to predict handover necessity so as to reduce the handover delay. The results show that the number of handovers is reduced by up to 50% compared to the conventional AHP. The results also show that the threshold crossing rate and average duration of fades are reduced by 47% compared with the AHP. Handover delay is also reduced by up to 40 ms due to RSS forecasting.

Geometry-Based Stochastic Model and Statistical Characteristic Analysis of Cell-Free Massive MIMO Channels

Cell-free massive multi-input multi-output (MIMO) systems exhibit many characteristics that differ from those of traditional centralized massive MIMO systems, and there are still research gaps in the modeling of cell-free massive MIMO channels. In this paper, a geometry-based stochastic model (GBSM) that combines the double-ring model and hemisphere model to comprehensively consider the distribution of scatterers in the environment was proposed for cell-free massive MIMO channels. Combined with the line-of-sight (LoS) path, single scattering path, and double scattering path components, the channel matrix between the access points (APs) and the user was derived. The proposed model fully considers geometric parameters such as the arrival/departure direction, elevation angle, time delay, and distance, which can accurately characterize the channel. Then, we proved that the traditional channel model, standard block-fading model, and spatial basis expansion model (SBEM) adopted in a cell-free massive MIMO system could not describe the nonstationarity in the space, time, and frequency domains, whereas the proposed GBSM could. Statistical characteristics of the channel were analyzed, including the space cross-correlation function (CCF), time autocorrelation function (ACF), Doppler power spectral density (PSD), level crossing rate (LCR), and average fade duration (AFD). Then, we investigated the proposed model by simulating the space CCF, time ACF, Doppler PSD, LCR, and AFD under the conditions of two different scatterer densities. Through simulations and analyses, some new features of cell-free massive MIMO channels were identified, providing a theoretical basis for in-depth research on cell-free massive MIMO systems. Finally, the measurement-based scenario and the WINNER II channel model are compared to demonstrate that the GBSM is more practical to characterize real cell-free massive MIMO channels.

IO-Link Wireless Sensitivity Testing Methods in Reverberation Chambers

Communication reliability is a challenging requirement, which implies the need for over-the-air (OTA) testing. Reverberation chambers (RCs) are widely used for OTA tests in various fields. Due to their properties, such as inherent radio channel emulation or the arbitrary orientation of the equipment under test (EUT) in the test volume, they can be used as advantageous test environments for wireless products in the field of industrial manufacturing automation, such as for the IO-Link Wireless (IOLW) standard. In this paper, the different OTA sensitivity test procedures total isotropic sensitivity (TIS), average fading sensitivity (AFS) and mean channel packet error (MCPE) method, which is based on the fundamental channel model of the wireless standard, are described and evaluated in various variants. A core aspect of the proposal is the impact of the possible use of frequency hopping of the wireless equipment under test. The respective advantages and disadvantages are shown. Overall, TIS proves to be a suitable alternative for IOLW OTA sensitivity testing.

A Non-Stationary 3D Model for 6G Massive MIMO mmWave UAV Channels

This paper proposes a non-stationary three-dimensional (3D) irregular-shaped geometry-based stochastic model (IS-GBSM) for fifth generation (5G) and beyond massive multiple-input multiple-output (MIMO) millimeter wave (mmWave) unmanned aerial vehicle (UAV) channels. This is the first sixth generation (6G) massive MIMO mmWave UAV IS-GBSM that can model the UAV channel space-time non-stationarity, and can describe the impact of some unique UAV-related parameters, e.g., the UAV’s moving direction, height, and speed, on channel statistical properties. To better represent the space-time non-stationarity in UAV scenarios, a novel UAV-related space-time cluster evolution algorithm is developed. The developed algorithm considers the characteristics of UAV communications on the modeling of space-time non-stationarity. Based on the proposed model, some channel statistical properties are derived and thoroughly investigated, including the space-time-frequency correlation function, Doppler power spectral density, envelope level crossing rate, and average fade duration. Some numerical results and interesting observations are given, and the impact of UAV-related parameters on channel statistical properties is explored, which can provide assistance for the design of 6G massive MIMO mmWave UAV communication systems. Finally, the applicability of the proposed model is verified by the close agreement between simulation results and measurement.

Mission Effective Capacity—A Novel Dependability Metric: A Study Case of Multiconnectivity-Enabled URLLC for IIoT

Various industrial Internet of Things applications demand execution periods throughout which no communication failure is tolerated. However, the classical understanding of reliability in the context of ultra-reliable low-latency communication (URLLC) does not reflect on the time-varying characteristics of the wireless channel. In this article, we introduce a novel mission reliability and mission effective capacity metric that takes these phenomena medium into account, while specifically studying multiconnectivity (MC)-enabled industrial radio systems. We assume uplink short packet transmission with no channel state information at URLLC user (the transmitter) and sporadic traffic arrival. Moreover, we leverage the existing framework of dependability theory and provide closed-form expressions (CFEs) for the mission reliability of the MC system using the maximal-ratio combining scheme. We do so by utilizing the mean time to first failure, which is the expected time of failure occurring for the first time. Moreover, we also derive exact CFEs for second-order statistics, such as level crossing rate and average fade duration, showing how fades are distributed in fading channels with respect to time. Furthermore, the design throughput maximization problem under the mission reliability constraint is solved numerically through the cross-entropy method.