Search

Auroral Ionosphere Model (AIM-E) is designed to calculate chemical content in the high-latitude E region ionosphere and takes into account both the solar EUV radiation and the electron precipitation of magnetospheric origin. The latter is extremely important for auroral ionosphere chemistry especially in disturbed conditions. In order to maximize the AIM-E timing accuracy when simulating highly variable periods in the course of geomagnetic storms and substorms, we suggest to parameterize the OVATION-Prime empirical precipitation model with the ground-based Polar Cap (PC) index. This gives an advantage to: (1) perform ionospheric simulation with actual input, since PC index reflects the geoeffective solar wind conditions; (2) promptly assess the current geomagnetic situation, since PC index is available in real-time with 1 min resolution. The simulation results of AIM-E with OVATION-Prime (PC) demonstrate a good agreement with the ground-based incoherent scatter radar data (EISCAT UHF, Tromso) and with the vertical sounding data in the Arctic zone during events of intense particle precipitation. The model reproduces well the electron content calculated in vertical column (90–140 km) and critical frequency of sporadic E layer (fOEs) formed by precipitating electrons. The AIM-E (PC) model can be applied to monitor the sporadic E layer in real-time and in the entire high-latitude ionosphere, including the auroral and subauroral zones, which is important for predicting the conditions of radio wave propagation. [ABSTRACT FROM AUTHOR]

Atmospheric impairment-induced attenuation is the prominent source of signal degradation in radio wave communication channels. The computation-based modeling of radio wave attenuation over the atmosphere is the stepwise application of relevant radio propagation models, data, and procedures to effectively and prognostically estimate the losses of the propagated radio signals that have been induced by atmospheric constituents. This contribution aims to perform a detailed prognostic evaluation of radio wave propagation attenuation due to rain, free space, gases, and cloud over the atmosphere at the ultra-high frequency band. This aim has been achieved by employing relevant empirical atmospheric data and suitable propagation models for robust prognostic modeling using experimental measurements. Additionally, the extrapolative attenuation estimation results and the performance analysis were accomplished by engaging different stepwise propagation models and computation parameters often utilized in Earth–satellite and terrestrial communications. Results indicate that steady attenuation loss levels rise with increasing signal carrier frequency where free space is more dominant. The attenuation levels attained due to rain, cloud, atmospheric gases, and free space are also dependent on droplet depths, sizes, composition, and statistical distribution. While moderate and heavy rain depths achieved 3 dB and 4 dB attenuations, the attenuation due to light rainfall attained a 2.5 dB level. The results also revealed that attenuation intensity levels induced by atmospheric gases and cloud effects are less than that of rain. The prognostic-based empirical attenuation modeling results can provide first-hand information to radio transmission engineers on link budgets concerning various atmospheric impairment effects during radio frequency network design, deployment, and management, essentially at the ultra-high frequency band. [ABSTRACT FROM AUTHOR]

We have developed a model that simulates the Poynting flux profile of the Saskatoon Super Dual Auroral Radar Network (SuperDARN) radar at ionospheric altitudes. The model uses ray tracing software to project the radar system's vacuum Poynting flux profile through the ionosphere, taking into account the influence of the ionospheric medium on the propagation characteristics of the high frequency radio waves. Measurements of the radar's transmissions by the Radio Receiver Instrument (RRI) in low‐Earth orbit are used to validate the model during five experiments which occurred between 4 and 8 August 2017. Comparisons between simulated and measured RRI antenna voltages show good agreement, although there are clear instances in which the model underperforms. Nevertheless, the model demonstrates its utility as a tool for interpreting RRI measurements of SuperDARN radars. The model also helps address a lack of knowledge of a SuperDARN radar's Poynting flux profile at ionospheric altitudes. In particular, we assess the assumption that SuperDARN's scattering volume lies along the great‐circle path of the transmitting beam's bearing. Comparisons between the model and RRI's measurements show that this assumption is reasonable for the five experiments investigated in this work. The model presents a new way of carrying out SuperDARN and high frequency radio science investigations. Plain Language Summary: The Super Dual Auroral Radar Network (SuperDARN) radar system located in Saskatoon, Canada is a powerful tool for studying the high‐latitude ionosphere. Even though the system has been operating nearly continuously since 1993, there is very little understanding of what the radar's Poynting flux profile looks like at ionospheric altitudes where its radar echoes originate. This is simply due to a lack of available measurements. As a result, it is customary to simply assume that the radar's Poynting flux profile at ionospheric altitudes resembles that of its Poynting flux profile in a vacuum projected along great‐circle trajectories up to ionospheric altitudes. This assumption is limited because it does not adequately account for the fact that the radar's Poynting flux profile can be influenced by the ionospheric medium in which it is immersed. In this work, we have developed a model of Saskatoon SuperDARN's Poynting flux profile at ionospheric altitudes which properly accounts for the influence of the ionosphere. Furthermore, we have compared the model's output to several measurements of the Saskatoon radar made by a radio receiver in low‐Earth orbit to validate the model. Our results show that the model is accurate and can be used as a useful tool for studying SuperDARN's Poynting flux profile at ionospheric altitudes. Key Points: The Saskatoon Super Dual Auroral Radar Network radar's Poynting flux profile is modeled in an empirical ionosphereA simulated Poynting flux profile is validated with the Enhanced Polar Outflow Probe Radio Receiver InstrumentThe Poynting flux model is a useful tool for studying high frequency radio wave propagation [ABSTRACT FROM AUTHOR]

5G networks are started to be deployed in urban areas in the dynamic spectrum sharing mode. Therefore, the analysis of Non-Line-of-Sight (NLOS) shadowing effects behind buildings of different heights becomes particularly important. The shadowing of GSM (900 MHz), UMTS (2100 MHz) and LTE (1800 MHz) technologies was investigated in the urban area. The results are examined by using the log-normal path loss model and four different stochastic equations, specifically: normal, log-normal, Rayleigh, and Nakagami. The results showed that the fluctuations of path losses in the urban area correspond to the model of lognormal path losses. However, path losses for individual buildings do not fit this model. Therefore, stochastic methods were used to analyse shadowing effects. A path loss model based on a differential stochastic equation was proposed. This model includes the following values: free space losses, path losses disturbance due to the shadowing effect, standard deviation σ, and a freely chosen parameter b. This model allows a very accurate estimate of the path losses of the three technologies. A clear correlation was observed between parameter b and standard deviation σ. [ABSTRACT FROM AUTHOR]

Summary: Due to the congestion of the spectrum and the need for wider bandwidths, ultrahigh throughput satellites (UHTSs) are moving towards the use of higher frequency bands (Q/V and W bands). These frequencies are however severely impaired by atmospheric phenomena causing attenuation, scintillation and depolarization and compromising the quality of service (QoS). In order to study the Earth‐space link, several experimental campaigns have been performed up to the Q band with geostationary (GEO) satellites. This paper introduces a new propagation experiment that will extend the characterization of the Earth‐space channel up to the W band and low Earth orbits (LEOs). [ABSTRACT FROM AUTHOR]

The first results of direct expedition measurements of atmospheric absorption of electromagnetic waves in the sub-terahertz frequency range of 0.1–1 THz, carried out in order to select an optimal site from the point of view of the microwave astroclimate for development of an observatory that can become an element of the radio interferometer of the Suffa observatory and, in the future, enter into collaboration with the Event horizon telescope (EHT), are presented in brief. The EHT, presenting an image of the shadow of a black hole, today consists of a dozen antennas located around the globe, and at present has no elements in its network in northern Eurasia. The studies performed may be useful not only for radio astronomy problems, but also for space communications, radar of the Moon, asteroids, and the detection of space debris objects. The first results of direct measurements of propagation of subterahertz waves at the selected sites confirmed the initial hypothesis of the expedition. This hypothesis was formulated on the basis of an analysis of meteorological data, as well as satellite data on atmospheric absorption in other ranges: optics and low-frequency radio bands. It was assumed that the work in the subterahertz frequency range in the eastern part of the northern Caucasus is more promising than in the western Caucasus. The western part is more attractive because today there are a number of observatories already operating, and the installation of one more antenna would have been much easier in terms of the necessary infrastructure and required highly qualified personnel. The hypothesis of the predominance of the eastern part was convincingly confirmed in the completed research by comparing the absorption in the 2- and 3-mm bands from the previously surveyed areas of the Western Caucasus (Terskol peak, Pastukhov mountain, KMO, BTA, RATAN-600 sites, etc.) with those studied during the expedition in 2021 for the Eastern sites on the Mayak (Gunib), Stolovaya, and Shalbuzdag mountains. Even measurements at the highest peak not only in the Western Caucasus, but also in Europe, at Mount Elbrus, carried out as part of this expedition, gave results worse than those in Dagestan and North Ossetia, confirming the futility of further search for a place for an effective subterahertz instrument in the eastern part of the North Caucasus. [ABSTRACT FROM AUTHOR]

The presence of large and small-scale irregularities TID of the ionosphere in the path of radio wave propagation from the navigation satellite to the GPS receiver is the main challenge for the application of ionospheric research to improve positioning accuracy using single-frequency receivers. In this paper, in contrast to the traditional methods of compensating for the error associated with the ionospheric delay (the Klobuchar method and the use of TEC values), we propose the calculation of the ionospheric delay by the ray tracing method in a model that is as close as possible to the real conditions. To achieve this proximity, a model is proposed that includes various types of TID irregularities. The corresponding algorithms are presented and the numerical results are given. It is shown that single large-scale TIDs can lead to errors of 10–30 m, errors due to small-scale TIDs do not exceed 2 m. © 2001 Elsevier Science. All rights reserved. • Positioning systems are highly dependent on the state of the ionosphere. • Ionospheric delay is a major source of positioning errors. • The greatest influence is exerted by irregularities. • A method is proposed for direct calculation of delays in a model with irregularities. • The core effect is influence of single large-scale irregularities. [ABSTRACT FROM AUTHOR]

The interaction of radio frequency waves as it propagates through a plasma medium – has fascinated the plasma physicists for decades. The ionosphere is crucial for radio wave propagation. Short radio waves reflect from the F-layer and spread over long distances (up to two-three thousand kilometers) due to a high altitude of the layer. Long and medium radio waves propagate in the E- and D-layers. The anisotropy of ionospheric plasma due to the Earth's magnetic field accounts for the presence of two radio wave components, ordinary (O-mode) and extraordinary (X-mode). Powerful, high-frequency (HF) radio waves can be used to temporarily modify the ionosphere. These controlled, active experiments have proven useful both for studies of the natural upper atmosphere through observations of the ionospheric response to HF-induced perturbations, and for basic physics investigations exploiting the ionosphere as a large, natural plasma laboratory-without-walls. Here, we study these wonderful aspects through a student project. [ABSTRACT FROM AUTHOR]

This is the second half of a two‐part study. In the first part, we had used the World Wide Lightning Location Network's (WWLN) recorded signal amplitudes to test a model of Very Low Frequency signal transmission from the lightning to each sensor. The model predicts a dramatic worsening of transmission at low magnetic latitudes, for nighttime propagation (compared to daytime propagation) toward magnetic West. However, we found that the use of amplitudes was ill‐adapted for testing the model under conditions of a deep outage of transmission. Since the relative weakening of nighttime transmission is rather counter‐intuitive, we have now developed an alternative approach to testing that model prediction. This alternative approach highlights the patterns of detection/non‐detection of several low‐magnetic‐latitude WWLLN stations and compares those patterns with the appropriate patterns of the model transmission. Key Points: Suppression of low‐latitude Very Low Frequency transmission propagating magnetic west, especially at nightSuppression at night applies to nearly the entire westward half‐plane, from magnetic South clockwise to magnetic NorthThe magnetic westward suppression at night is readily observable for dip angles in the range −30° to +30° [ABSTRACT FROM AUTHOR]

In telecommunication channel modelling the wavelength is small compared to the physical features of interest, therefore deterministic ray tracing techniques provide solutions that are more efficient, faster and still within time constraints than current numerical full-wave techniques. Solving fundamental Maxwell's equations is at the core of computational electrodynamics and best suited for modelling electrical field interactions with physical objects where characteristic dimensions of a computing domain is on the order of a few wavelengths in size. However, extreme communication speeds, wireless access points closer to the user and smaller pico and femto cells will require increased accuracy in predicting and planning wireless signals, testing the accuracy limits of the ray tracing methods. The increased computing capabilities and the demand for better characterization of communication channels that span smaller geographical areas make numerical full-wave techniques attractive alternative even for larger problems. The paper surveys ways of overcoming excessive time requirements of numerical full-wave techniques while providing acceptable channel modelling accuracy for the smallest radio cells and possibly wider. We identify several research paths that could lead to improved channel modelling, including numerical algorithm adaptations for large-scale problems, alternative finite-difference approaches, such as meshless methods, and dedicated parallel hardware, possibly as a realization of a dataflow machine.

The accurate prediction of radio wave propagation is extremely important for wireless network planning and optimization. However, inexact matching between the traditional empirical model and actual propagation environments, as well as the insufficiency of the sample data required for training a deep learning model, lead to unsatisfactory prediction results. This paper proposes a field strength prediction model based on a deep neural network that is aimed at a tiny dataset composed of the geographic information and corresponding satellite images of a target area. This model connects two pretrained networks to minimize the parameters to be learned. Simultaneously, a convolutional neural network (CNN) model is constructed for comparison based on a previous advanced study in this field. Experimental results show that the proposed model can obtain the same accuracy as that of previously developed CNN models while requiring less data. [ABSTRACT FROM AUTHOR]

With the given scope for new use cases and the demanding needs of future 6th generation (6G) wireless networks, the development of wireless communications looks exciting. The propagation medium has been viewed as a randomly behaving entity between the transmitter and the receiver since traditional wireless technology, degrading the quality of the received signal due to the unpredictable interactions of the broadcast radio waves with the surrounding objects. On the other hand, network operators could now manipulate electromagnetic radiation to remove the negative impacts of natural wireless propagation due to the recent arrival of reconfigurable intelligent surfaces (RIS) in wireless communications. According to recent findings, the RIS mechanism benefits nonorthogonal multiple access (NOMA), which can effectively deliver effective transmissions. For simple design, of RIS-NOMA system, fixed power allocation scheme for NOMA is required. The main system performance metric, i.e., outage probability, needs to be considered to look at the efficiency and capability of transmission mode relying on RIS and NOMA schemes, motivated by the potential of these developing technologies. As major performance metrics, we derive analytical representations of outage probability, and throughput and an accurate approximation is obtained for the outage probability. Numerical results are conducted to validate the exactness of the theoretical analysis. It is found that increasing the higher number of reflecting elements in the RIS can significantly boost the outage probability performance, and the scenario with only the RIS link is also beneficial. In addition, it is desirable to deploy the RIS-NOMA since it is indicated that better performance compared with the traditional multiple access technique. [ABSTRACT FROM AUTHOR]

Connected car has become one of emerging technology in the automotive industries today. This development preludes a rise in vehicular communication studies that primarily targets radio channel modelling on vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2I) communication mode. Considering vehicular obstruction, vast channel propagation studies have focused more on V2V mode while others consider the typical urban scenarios consisting of high traffic volumes of moving vehicles. Due to challenging propagation mechanisms and high complexity in such areas, radio propagation models applied in simulators assume an obstacle-free environment rather than considering the least effect imposed by metal obstruction on communication signal. Besides, there are limited studies pertaining to metal obstruction that considers several under-explored environments such as actual parking lots, junctions and other road infrastructure support. As such, this paper demonstrates signal attenuation analysis caused by the presence of metal objects in low density over obstacle-free environment on actual parking lot via V2I mode. Two scenarios such as LOS and NLOS conditions consisting of obstacle-free, cars and buses as static metal objects are evaluated. The aim of this research is to characterize signal strength caused by metal blockage on radio wave propagation predicated on the presence of vehicles as a subject of obstruction in comparison to obstacle-free vehicular environment. The validity of data is shown through received signal strength indicator (RSSI) and approximation analysis (RMSE) to demonstrate the efficiency of obtained measurements. The results demonstrated that Log-normal shadowing model yields the best fit to low-density metal obstruction scenario with smallest RMSE of 4.78 under bus obstruction whereas 5.72 under car obstruction. [ABSTRACT FROM AUTHOR]

Throughout the wireless communication network planning process, efficient signal reception power estimation is of great significance for accurate 5 G network deployment. The wireless propagation model predicts the radio wave propagation characteristics within the target communication coverage area, making it possible to estimate cell coverage, inter-cell network interference, and communication rates, etc. In this paper, we develop a series of features by considering various factors in the signal transmission process, including the shadow coefficient, absorption coefficient in test area and base station area, distance attenuation coefficient, density, azimuth angle, relative height and ground feature index coefficient. Then we design a quantile regression neural network to predict reference signal receiving power (RSRP) by feeding the above features. The network structure is specially constructed to be generalized on various complex real environments. To prove the effectiveness of proposed features and deep learning model, extensive comparative ablation experiments are applied. Finally, we have achieved the precision rate (PR), recall rate (RR), and inadequate coverage recognition rate (PCRR) of 84.3%, 78.4%, and 81.2% on the public dataset, respectively. The comparison with a series of state-of-the-art machine learning methods illustrates the superiority of the proposed method. [ABSTRACT FROM AUTHOR]

The plasma sheath formed around a hypersonic vehicle traveling through the atmosphere will affect the quality of wireless signals. To fully grasp this effect, it is necessary to comprise the vehicle antennas in the investigations, which is considered in our work. Firstly, the discrete plasma sheath data is generated by using COMSOL. Then, combining the shift-operator Finite-Difference Time-Domain method and numerical methods such as the high-dimensional Lagrange interpolation, an electromagnetic algorithm designed for the discrete plasma sheath data is developed. Based on this, the influence of the plasma sheath on the radio wave propagation is studied under different flight condition. Results show that, due to the influence both of the plasma sheath and of the vehicle antenna, the radio waves exhibit rich propagation behaviors, such as the frequency-band shift and the tail diffraction, etc. Compared with other studies, the results in this paper more approximately reflect the propagation characteristics of radio waves in the hypersonic environment, and can provide a reference for the related applications. [ABSTRACT FROM AUTHOR]

Sum‐rate optimization problem is a key issue in a time‐varying multi‐user multi‐input multi‐output (MU‐MIMO) distributed antenna system. Channel precoding matrix is the key technology in the achievable sum‐rate optimization problem. In this paper, two algorithms are proposed to solve the achievable sum‐rate optimization problem for a time‐varying MU‐MIMO distributed antenna system, namely one‐dimensional search algorithm (OSA) and cyclic MMSE (Minimum Mean Square Error) search algorithm (CMSA). In order to design the channel precoding matrix for the achievable sum‐rate optimization, a one‐dimensional search algorithm is proposed in the time‐varying MU‐MIMO distributed antenna system. For the problem with a large amount of computation in OSA, a cyclic MMSE search algorithm is proposed in the time‐varying MU‐MIMO distributed antenna system. Simulation results show that the proposed algorithms can effectively improve the sum‐rate compared to other algorithms. Simulation results also show that OSA is superior to CMSA in the sum‐rate, and the channel state information (CSI) coefficient has little effect on OSA and CMSA. [ABSTRACT FROM AUTHOR]

In clustered distributed storage systems (CDSSs), one of the main design goals is minimizing the transmission cost during the failed storage nodes repairing. Generalized regenerating codes (GRCs) are proposed to balance the intra‐cluster repair bandwidth and the inter‐cluster repair bandwidth for guaranteeing data availability. The trade‐off performance of GRCs illustrates that, it can reduce storage overhead and inter‐cluster repair bandwidths simultaneously. However, in practical big data storage scenarios, GRCs cannot give an effective solution to handle the heterogeneity of bandwidth costs among different clusters for node failures recovery. This paper proposes an asymmetric bandwidth allocation strategy (ABAS) of GRCs for the inter‐cluster repair in heterogeneous CDSSs. Furthermore, an upper bound of the achievable capacity of ABAS is derived based on the information flow graph (IFG), and the constraints of storage capacity and intra‐cluster repair bandwidth are also elaborated. Then, a metric termed global repair bandwidth cost (GRBC), which can be minimized regarding of the inter‐cluster repair bandwidths by solving a linear programming problem, is defined. The numerical results demonstrate that, maintaining the same data availability and storage overhead, the proposed ABAS of GRCs can effectively reduce the GRBC compared to the traditional symmetric bandwidth allocation schemes. [ABSTRACT FROM AUTHOR]

This paper investigates the problem of multi‐user anti‐jamming channel access with partially overlapping channels (POC). Compared with traditional anti‐jamming systems that use non‐overlapping channels, POC improve the spectral efficiency. However, the partial overlap of channels also brings more serious interference. For this, physical distance and channel separation on the interference intensity under partially overlapping channels are first considered and the malicious jamming and interference among users are formulated as a hierarchical binary model. Secondly, to cope with multi‐user decisions under dynamic jamming conditions, the Markov game framework is adopted to analyse the problem. Thirdly, a multi‐user collaborative anti‐jamming channel selection algorithm based on reinforcement learning is proposed as well as the optimal anti‐jamming strategy can be obtained. Finally, the simulation results validate that the proposed algorithm helps users cope with jamming and eliminate mutual interference. Compared with the non‐overlapping channel access scheme, the POC access scheme achieves higher network throughput. [ABSTRACT FROM AUTHOR]

Low latency beamforming using phased antenna arrays is the key for practical deployment of envisioned millimetre wave (mmWave) Gbps mobile networks. This work aims towards reducing the overhead of the exhaustive sector‐level sweep phase of the analog beamforming adopted in the IEEE 802.11ad standard. This work is the first to propose the use of reconfigurable antenna single RF chain in the sub‐6 GHz new radio (NR) band to aid codebook‐based beam selection in the mmWave band of the NR. We exploit the congruence between the spatial propagation signatures of signals at both mmWave and sub‐6 GHz frequencies to reduce the beam search space. The simulation results show a significant reduction in mmWave beam search overhead up to 70% on average and 80% with an average gain loss of 3dB. [ABSTRACT FROM AUTHOR]

In amplitude modulation radio-based passive radar, the track-before-detect (TBD) procedures are performed to process long time observation data. This work mainly focuses on the tracking of the time-Doppler and time-azimuth traces of multiple target under real scenarios such as low signal-to-noise ratio, hybrid clutter, severe breaking points, and intersecting traces. A new original approach to deal with the TBD problem of this work is developed. Two types of linear equations according to the simplified radio wave propagation model are formulated, which is the key point of the proposed method. We make the theoretical analysis about how the linear equations can be used to track multiple target, and how multiple target's constant velocities and initial positions can be estimated, which is an additional parameter estimation capability of the proposed method. Both the simulated data and real experimental data are performed with the proposed method and some conventional TBD methods. Several comparisons of the results are given to verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Analysis of the variation in galactic cosmic rays and changes in various characteristics of Forbush effects associated with the influence of interacting solar wind disturbances on the Earth (disturbances with a time interval between registration of less than 50 h) is presented based on the database of Forbush effects and interplanetary disturbances developed at the Institute of Terrestrial Magnetism, Ionosphere, and Radio Wave Propagation. Cases of the pair interaction of high-speed streams from coronal holes and coronal mass ejections in 1995–2019 are considered, and the behavior of the solar wind parameters, the interplanetary magnetic field, and the cosmic ray variations for two types of interacting solar wind disturbances (the interaction of successive coronal mass ejections and the interaction of a coronal mass ejection with a high-speed coronal hole stream) are analyzed. It is found that the average times of the onset of the Forbush effect minimum and the record of the maximum solar wind velocity and the absolute value of the interplanetary magnetic field decrease for the first of a pair of interacting events, i.e., the second events of the pair do not allow the first to develop fully. It is also found that the presence of interaction enriches the second event at the expense of the resources of the first. This increases its geomagnetic efficiency and the degree of cosmic ray modulation in comparison with isolated events. [ABSTRACT FROM AUTHOR]

This paper takes the annular solar eclipse that occurred in China on June 21, 2020, as the background and conducts tests and analysis of shortwave timing sky wave signals. The test group continuously tested the signal field strength data from June 20, 2020, to June 23, 2020. The results show that the shortwave signal field strength on June 21, the day of the annular eclipse, is significantly weaker than that on two other days—before and during the annular eclipse—and there are three obvious jumps in the field strength value. (1) The first jump occurs more than one hour before the annular eclipse, and then, the field strength has an oscillatory attenuation. Between the first jump and the second jump, the overall change trend of the field strength value is an oscillatory decline one. (2) About 25 min before the beginning of the eclipse, the second jump of the field strength occurs; from the second jump to the third jump, that is, before the occurrence of the beginning of the eclipse and the transition phase from the beginning to the middle of the eclipse, the value of the field strength has an oscillatory increase. (3) During the period of 8:00–8:10, the field strength shows a third jump. Although the field strength oscillates after the third jump, it has no obvious increasing or decreasing trend. Based on the results of previous studies on the annular eclipse on that day and the analysis of the theoretical model of radio wave propagation, this paper preliminarily considers that the change in signal field strength is supposed to be caused by the impact of the outbreak of the annular eclipse on the ionosphere. When the annular eclipse occurred, the sunlight reaching the ground is blocked by the Moon, and the ionization degree of electrons in the ionosphere is reduced, resulting in an increase in the penetration factor, and the overall performance of the shortwave signal reaching the ground is weakened. [ABSTRACT FROM AUTHOR]

With the arrival of 5G wireless communication systems, there has been increased interest in exploring higher frequency bands above 6 GHz, up to millimeter-wave frequencies. Radio wave propagation at these higher frequencies can suffer from substantial Doppler impairments. The linear dependency of Doppler shifts with carrier frequencies make them challenging to use in high-mobility 5G cellular scenarios. Therefore, the Doppler power spectrum (DPS) characteristics and radio channel coherence time (CT) of the received signals are of great importance for 5G wireless systems. In this way, this paper presents the effects of a narrow beam phased antenna array in reducing the DPS (due to user movement) and, simultaneously, increasing the coherence time (CT). Functional and complete descriptive assessments of beamwidths versus the DPS and CT, through different elements and geometries of the phased antenna array, are analyzed. Moreover, in terms of CT and the DPS, better performance on the 5G cellular scenarios was obtained. [ABSTRACT FROM AUTHOR]

In this study, efficient channel characterisation and modelling based on deep learning algorithms are developed and presented in a line‐of‐sight (LOS) scenario. The learning and the validation processes are performed using measurements from only one environment, enabling robust model learning and prediction results. Then, the model efficiency is analysed and validated using measurements from different environments that are not included in the learning process. Finally, the channel characterisation is made with the predicted and measured ones. The designed model achieved a highly accurate channel frequency response prediction within different environments without any prior information. The model root‐mean‐square error achieves up to 2% compared with the latest proposed models in the literature. Hence, an efficient modelling tool is provided for the future wireless communication design in a complex confined environment in LOS scenarios. [ABSTRACT FROM AUTHOR]

• Availability area analysis of distance measuring equipment global network. • Service volume is estimated based on path loss model. • Distance measuring equipment. • DME service can be provided only in 27.76% of global airspace. Safety of air transportation strongly depends on the performance of on-board positioning sensors. Positioning by data from navigational aids is considered by international aviation community as one of the main stand-by positioning approaches onboard of civil airplanes. However, only positioning by pair of distance measuring equipment (DME) meets requirements of Performance-Based Navigation. A DME service volume model based on path loss between a pair of transmitting and receiving antennas has been proposed in the paper. The model takes into account the influence of relief on radio waves propagation and diffraction from high-altitude elements of relief. The proposed model has been used in the analysis of DME global network performance. In particular, performance of a global network is analyzed based on availability area of DME service, area of positioning by pairs of DME/DME support, availability of particular positioning accuracy, and areas of meeting various RNAV requirements. Obtained results indicate that only in 27.76% of global airspace a DME service can be provided. However, only within 15.9% of airspace, a DME/DME positioning can be used. Results of the analysis indicate about the necessity of actions for further development of global navigational aids network in order to guarantee safe airlines connections around the globe. [ABSTRACT FROM AUTHOR]

Vehicular Visible Light Communication (VVLC) is preferred as a vehicle to everything (V2X) communications scheme due to its highly secure, low complexity and radio frequency (RF) interference free characteristics, exploiting the line of sight (LoS) propagation of visible light and usage of already existing vehicle light emitting diodes (LEDs). Current VVLC channel models based on deterministic and stochastic methods provide limited accuracy for path loss prediction since deterministic methods heavily depend on site-specific geometry and stochastic models average out the model parameters without considering environmental effects. Moreover, there exists no wireless channel model that can be adopted for channel frequency response (CFR) prediction. In this paper, we propose a novel framework for the machine learning (ML) based channel modeling of the VVLC with the goal of improving the model accuracy for path loss and building the CFR model through the consideration of multiple input variables related to vehicle mobility and environmental effects. The proposed framework incorporates multiple measurable input variables, e.g., distance, ambient light, receiver inclination angle, and optical turbulence, with the exploitation of feed forward neural network based multilayer perceptron neural network (MLP-NN), radial basis function neural network (RBF-NN) and decision tree based Random Forest learning methods. The framework also includes data pre-processing step, with synthetic minority over sampling technique (SMOTE) data balancing, and hyper-parameter tuning based on iterative grid search, to further improve the accuracy. The accuracy of the proposed ML based channel modeling is demonstrated on the real world VVLC vehicle-to-vehicle (V2V) communication channel data. The proposed MLP-NN, RBF-NN and Random Forest based channel models generate highly accurate path loss predictions with 3.53 dB, 3.81 dB, 3.95 dB root mean square error (RMSE), whereas the best performing stochastic model based on two-term exponential fitting provides prediction accuracy of 7 dB RMSE. Moreover, MLP-NN and RBF-NN models are demonstrated to predict VVLC CFR with 3.78 dB and 3.60 dB RMSE, respectively. [ABSTRACT FROM AUTHOR]

The rocket exhaust, as a source of the disturbance, provides a way to examine physical and chemical phenomena in the ionosphere. Since the disturbance morphological characteristics are closely related to rocket orbit, the ionospheric perturbation produced by the rocket exhaust considering the trajectory effect is simulated. The three-stage booster rocket trajectory is calculated, considering multi-stage thrust, aerodynamic drag, gravity and apparent force. Based on trajectory calculation and the electron density depletion theory of neutral gas injected into ionosphere, the exhaust is divided into a series of mass elements released at different time and different positions along the trajectory. The theory considers the charge exchange between the ambient O+ ions and the high-speed exhaust molecules (primarily H 2 O) in the exhaust plume. The simulation results show that the depletion structure restricted by the trajectory are dramatically different from the structure produced by a point source release, meaning that it no longer appears as an isotropic quasi-symmetric distribution, but the overall orientation of the depletion structure is consistent with the trajectory direction. Furthermore, the ray tracing technique is used to simulate the propagation of radio waves passing through the depletion structures. Due to the steepness of the depletion boundary and the difference in the shape of the boundary, the "focusing" effect of the rays which though the disturbance structure restricted by the trajectory disappear. These characteristics results can be an important reference for rocket detection and identification. [ABSTRACT FROM AUTHOR]

Wireless multipath clustering is an important area in channel modeling, and an accurate channel model can lead to a reliable wireless environment. Finding the best technique in clustering wireless multipath is still challenging due to the radio channels’ time-variant characteristics. Several clustering techniques have been developed that offer an improved performance but only consider one or two parameters of the multipath components. This study improved the K-PowerMeans technique by incorporating weights or loads based on the principal component analysis and utilizing the Minkowski distance metric to replace the Euclidean distance. K-PowerMeans is one of the several methods in clustering wireless propagation multipaths and has been widely studied. This improved clustering technique was applied to the indoor datasets generated from the COST 2100 channel Model and considered the multipath components’ angular domains and their delay. The Jaccard index was used to determine the new method’s accuracy performance. The results showed a significant improvement in the clustering of the developed algorithm than the standard K-PowerMeans. [ABSTRACT FROM AUTHOR]

Copyright of Baghdad Science Journal is the property of Republic of Iraq Ministry of Higher Education & Scientific Research (MOHESR) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Subject and Purpose. The article is devoted to the modeling of electromagnetic field backscattering in the millimeter and centimeter wave regions. The relevance of such studies proceeds from the need to have wave scattering characteristics of various objects at the modeling stage. The aim of the work is to determine an acceptable step size of the surface discretization, no matter whether a well-known or perspective method of the scattered field calculation is used. Methods and Methodology. To achieve the goal as defined, mathematical and statistical modeling methods are used. The modeling and theoretical results are compared. Results. Numerical simulations of the electromagnetic field scattering have been performed using the Fresnel-Kirchhoff diffraction formula and the method of surface representation by a set of elementary flat faces. For such simplest objects as a ball and a plane, a comparison of the theoretical and modelling results on effective scattering surface has been performed and made it possible to determine an acceptable step size of the surface discretization in the electromagnetic field backscattering. It has been shown that once the surface discretization has been chosen properly, the determination of the field strength by the Fresnel-Kirchhoff method provides an effective scattering surface value that coincides with the theoretical results most accurately. Conclusion. It has been shown that the Fresnel-Kirchhoff method describes basic properties of the scattered field most well. The employment of the modeling method of surface representation by a set of flat faces with relevant scattering patterns requires a normalization of the results with the relevant theoretical and experimental data taken into account.

This paper is focused on solving the inversion problem of refractivity from clutter (RFC) technique. A novel hybrid model is developed that can estimate the atmospheric refractivity (M profile) with a high accuracy, for surface based duct case, which is most effective non¬standard propagation condition on radar observation. The model uses propagation factor curve in horizontal axis, whose characteristics is determined by M profile for esti¬mation. The model is based on artificial neural network, which includes a dynamic training data approach, and a problem adapted genetic algorithm. Dynamic training data set application is a nonstandard approach in neural network applications, in which every obtained result are dynamically added to data set during the estimation pro¬cess, for a better estimation. Firstly, neural network and genetic algorithm have been adapted to the characteristics of inversion problem separately. Then, the mentioned two methods have been harmonized and run together. Ulti-mately, the final algorithm has evolved into a complex adapted hybrid model, which is easily applicable to clutter data obtained by any real radar from the real environment. The results show that the proposed model presents consid¬erably effective solution to refractivity estimation problem.

We present an inversion scheme of the backscatter signal leading edge into parameters of the quasi-parabolic electron density profile, which is based on the comparison of experimental and calculated minimum delays of scattered signals with corresponding distance to the skip zone border. Input parameters are frequency dependences of minimum group path of signal propagation, derived from processing and interpreting backscatter ionograms. For a fixed sounding frequency, the ionospheric parameter pair — the critical frequency and height of the F2-layer maximum — is defined as the intersection point of two curves representing solutions of minimization problems for discrepancy functionals of the minimum group path and the range to the skip zone border. Determining the ionospheric parameters by this inversion scheme on the sounding frequency grid allows us to construct a two-dimensional distribution of electron density in the direction of backscatter sounding.

An asymptotic solution of ray equations is used for numerical simulation of the electromagnetic wave propagation in a smoothly non-uniform Earth-ionosphere duct. Being an extension of the adiabatic invariant approach, our method allows one to easily calculate and visualize all descriptive and energetic characteristics of global HF radio waves, including transition between multi-hop and ricochet propagation modes, antipodal focusing, geometric divergence and ohmic absorption. A quasi-parabolic model of F2 layer with the parameters taken from the international model IRI-2012 is used in numerical examples. From the mathematical point of view, it is an example of two-scale asymptotic expansion in a small parameter ν ~ H/L ~ L/πR where H is a characteristic height of the ionospheric layer, L is the scale of its horizontal non-uniformity, R is the Earth radius.

Aiming at the problem that it is difficult to balance the accuracy and velocity of the fixed-step solution of standard parabolic equation in the study of radio wave propagation in a wide range of complex environments, a variable-step solution method of standard parabolic equation is proposed. Firstly, after deducing the relationship between the error of SSFT solution and step size, frequency and other factors; And the basic selection range of step size for SPE variable step size solution is given. Secondly, the action mechanism of different environmental factors and the requirement of changing trend for step size are expounded through simulation, and the complex environment of SPE application is classified according to the requirement of error. Finally, the method is used to simulate the characteristics of the typical complex environment. The simulation results show that the method can save up to 71.4% of the time compared with the fixed-step method of parabolic equation under the condition of ensuring the calculation accuracy. The reliability and efficiency of the proposed method are verified, and the calculation efficiency of the parabolic equation radio wave prediction can be greatly improved. Therefore, the parabolic equation method with variable step size can ensure the accuracy of calculation, reduce the memory and time required for calculation, greatly improves the efficiency of calculation, and has practical significance in the application of real-time prediction of electromagnetic wave propagation in a wide range of complex environments.

The equatorial plasma bubble (EPB) phenomenon is an important component of space weather as the ionospheric irregularities that develop within EPBs can have major detrimental effects on the operation of satellite-based communication and navigation systems. Although the name suggests that EPBs occur in the equatorial ionosphere, the nature of the plasma instability that gives rise to EPBs is such that the bubbles may extend over a large part of the global ionosphere between geomagnetic latitudes of approximately ±15°. The scientific challenge continues to be to understand the day-to-day variability in the occurrence and characteristics of EPBs, such as their latitudinal extent and the development of irregularities within EPBs. In this paper, basic theoretical aspects of the plasma processes involved in the generation of EPBs, associated ionospheric irregularities, and observations of their characteristics using different techniques will be reviewed. Special focus will be given to observations of scintillations produced by the scattering of VHF and higher frequency radio waves while they propagate through ionospheric irregularities associated with EPBs, as these observations have revealed new information about the non-linear development of Rayleigh–Taylor instability in equatorial ionospheric plasma, which is the genesis of EPBs.

A mixed semiclassical initial value representation expression for spectroscopic calculations is derived. The formulation takes advantage of the time-averaging filtering and the hierarchical properties of different trajectory based propagation methods. A separable approximation is then introduced that greatly reduces (about an order of magnitude) the computational cost compared with a full Herman-Kluk time-averaging semiclassical calculation for the same systems. The expression is exact for the harmonic case and it is tested numerically for a Morse potential coupled to one or two additional harmonic degrees of freedom. Results are compared to full Herman-Kluk time-averaging calculations and exact quantum wavepacket propagations. We found the peak positions of the mixed semiclassical approximations to be always in very good agreement with full quantum calculations, while overtone peak intensities are lower with respect to the exact ones. Given the reduced computational effort required by this new mixed semiclassical approximation, we believe the present method to make spectroscopic calculations available for higher dimensional systems than accessible before. [ABSTRACT FROM AUTHOR]

Extremely low-frequency (ELF: below 30 Hz) wave penetration theory in the layered oceanic lithosphere is essential for studying submarine communications. In this article, we investigate the mode theory of ELF wave propagation in a layered oceanic lithosphere waveguide. Based on the real situation of the oceanic lithosphere approximated by the stratified prototype, in which a low-conductivity layer lies between two overlying and underlying high-conductivity regions, a theoretically sound physical model of oceanic lithosphere waveguide is built. The modal equations for transverse magnetic (TM) and transverse electric (TE) polarized guided modes are delivered using surface impedance boundary conditions. By evaluating the reflection coefficients of the upper and lower waveguide boundaries, formulas for the modal equation’s roots are derived. Analytical expressions for propagable mode parameters, such as the phase velocity, attenuation rate, excitation factor, and the field strength for different components, are obtained, and the cutoff frequency for high-order modes is given. Computations show that the field component curves exhibit typical peaks and nulls associated with multiple-mode propagation in the waveguide region, with each mode traveling at different phase velocities and attenuation rates. Moreover, it is found that all the high-order modes are evanescent below the cutoff frequency. [ABSTRACT FROM AUTHOR]

On‐body propagation channels show significant polarization selectivity that has dominant impacts on the on‐body link quality in wireless body area networks. For on‐body relay channels over long distances across the body, the antenna polarization configurations of the relaying nodes are crucial to determine the relay performance, thereby requiring polarization optimization schemes. In this article, narrow band flat‐fading on‐body channels at 2.484 GHz are measured to analyse their polarization distribution above the skin under static postures. The measured on‐body channels show full‐space polarization convergence and dispersion, which are modelled by an extended 3 by 3 channel polarization matrix, and a statistical channel model is also proposed. Multi‐hop polarized on‐body relay channels are analysed on the relay link capacity, which shows polarization dependency between adjacent hop channels when relaying nodes are mounted by linearly polarized antennas. Both regular and iterative polarization selection algorithms are then designed to optimise the antenna polarization configuration of the nodes. Simulations based on the proposed polarization distribution model show significant link capacity increases for two‐hop and tfhree‐hop on‐body relay channels by the optimization algorithms. The results confirm the necessity of proper polarization selection schemes for on‐body relay channels. [ABSTRACT FROM AUTHOR]

To study the problem of radio wave propagation in an environment of dielectric ground and obstacles, especially in low‐lossy obstacles, to consider the propagation inside the obstacle, a new method is proposed to solve the two‐way parabolic equation based on the principle of domain decomposition. First, a mathematical model of parabolic equations for reflection and refraction in an environment with obstacles is established. Then, the area of the obstacle is decomposed into two different subdomains; the discrete mixed Fourier transform is used to calculate the field value in the upper subdomain from the top of the obstacle to the absorption boundary, the finite difference method is used to calculate the field value of the lower subdomain inside the obstacle, and the field strengths and phases of the two subdomains coordinate with the boundary conditions. In the process of calculation, we emphatically consider the multiple reflection and transmission paths inside obstacles to make the algorithm results more accurate. In addition, we verified the stability and convergence of the method. Finally, the simulation results show that the proposed method and the method of moments have good consistency, so the algorithm has the characteristics of strong applicability and fast calculation speed, which provide a novel and reliable method to research the wave propagation problem in a modified environment of obstacles. [ABSTRACT FROM AUTHOR]

Abstract—Studying the spatiotemporal dynamics of the disturbances in the atmosphere, upper, and lower ionosphere requires integrated investigation of interrelated processes at different heights in the different solar-geophysical conditions. The radiophysical complex at the Geophysical observatory "Mikhnevo" of the Institute of Geosphere Dynamics of the Russian Academy of Sciences (IDG RAS) which includes magnetic and electrophysical equipment, radio receiving systems, acoustic instruments, and ionospheric sounders provides data on the structure and dynamics of the ionospheric plasma in the midlatitude European part of Russia. The data from ULF/VLF receivers and measurements of GNSS signals are used to study synchronous variations caused in the lower and upper ionosphere by the magnetic storms, solar X-ray flares, and experiments on artificial modification of the ionosphere. The techniques are developed for processing the multi-instrumental measurements of the variations in the physical fields. They include the methods for reconstructing the absolute ionospheric total electron content (TEC) and electron density profile in the lower ionosphere. The obtained data are used for verifying the IDG RAS models of the lower ionosphere. [ABSTRACT FROM AUTHOR]

All empirical models of the ionosphere electron density profile rely, among other parameters, on the efficient description of the thickness of the F2 layer that controls the profile shape. Considering the trend towards data assimilation in such models to give near real time 3D specification of the electron density, the efficiency of such description becomes particularly important. This paper discusses the thickness parameters of the International Reference Ionosphere (IRI) and NeQuick2 empirical models and their effects on the modeled electron density profiles by comparing them with experimentally derived profiles. A simple technique to optimize the use of experimental data to forecast electron density specifications is proposed. It is based on the previous output of the assimilation of NmF2, hmF2, with the addition of the experimentally computed thickness parameters of the IRI and NeQuick models. This technique appears to be able to forecast reasonably well the electron density profile at least 30 min ahead of a given epoch. The possible use of such electron density profile forecast, for applications in HF radio waves propagation is suggested. [ABSTRACT FROM AUTHOR]

This paper presents the verification of indoor propagation channel simulations based on an intelligent ray launching algorithm (IRLA) in the Ka‐band of the millimeter‐wave (mmWave) spectrum in various indoor environments, including a classroom, an office, and a corridor, by radio channel measurements. Power delay profiles (PDPs), path loss, and root‐mean‐square (RMS) delay spreads were obtained from both the simulation results and the measurement results. Moreover, parameters of two site‐general path loss models, the close‐in free space reference distance path loss model and the floating‐intercept path loss model, were estimated based on the measured and simulated path loss. The comparison between the simulation results and the measurement results indicates that the IRLA‐based simulation can accurately describe the main characteristics of the indoor propagation channel in the Ka‐band. Key Points: Intelligent ray launching algorithm (IRLA) based channel simulations in three‐dimensional (3‐D) indoor environment modelsRadio channel measurements in indoor environments in the Ka‐band of the millimeter‐wave (mmWave) spectrumComparison of power delay profiles (PDPs), path loss, and root‐mean‐square (RMS) delay spreads between simulation and measurement results [ABSTRACT FROM AUTHOR]

When designing and maintaining a wireless network, engineers need to first evaluate the impact of a specific propagation environment on radio wave propagation. Currently, although many popular propagation models (PMs) are available for reference, their analysis and validation in ultrarugged terrain areas (uRTAs) are still underexplored. This article aims to implement an uRTA PM (uRTAPM), which consists of two modes, i.e., the point-to-point (uRTAPM-P2P) and the point-to-area (uRTAPM-P2A) modes, to meet the requirements of practical applications. First, we consider the digital elevation model (DEM) data sets and three types of propagation, i.e., line of sight (LOS), non-LOS (NLOS), and multiobstacle propagation. Second, we propose a cone multipath model to simulate the NLOS diffraction behavior caused by mountains. Third, we utilize a triangulated irregular network (TIN) to finely divide the terrestrial surface of uRTAs. Finally, based on numerical calculations, compared with the existing commonly used PMs, the uRTAPM is found to reveal more details about the propagation loss (PL) caused by the terrain in uRTAs. The measurements demonstrate that the mean absolute error (MAE), root-mean-square error (RMSE), and standard deviation (SD) between the uRTAPM predicted values and the actual measured values are lower than those of other methods. [ABSTRACT FROM AUTHOR]

The possibility of using millimeter-wave (MM) satellite communication lines in the Arctic to ensure reliable and high-speed communication is considered. The main problem for the application of MM waves is the possible meteorological conditions for the propagation of radio waves in the cold. Vertical profiles of meteorological data for a pair of islands in the Arctic Ocean were used to calculate molecular absorption on a possible link. A very simple model of attenuation of radio waves in rain on such a line is proposed. The satellite orbits for calculating the line attenuation margin were assumed as in the existing satellite system Gonets operating at frequencies of 300/400 MHz. The results of calculations show that satellite communications in the MM band are possible in the Arctic. [ABSTRACT FROM AUTHOR]