Radio Wave Propagation Research Articles

Higher Order FD-Padé Scheme for 3-D Parabolic Equation in Radio-Wave Propagation

This letter presents a higher-order finite-difference (FD) and Padé approximations method for the three-dimensional (3D) parabolic equation (PE) to predict radio-wave propagation. This method uses a 4 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{\boldsymbol {th}}$</tex-math></inline-formula> -order FD approximation of the differential operator in the transverse direction and a higher-order Padé approximation of the operator in the propagation direction. The 4 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{th}$</tex-math></inline-formula> -order FD and higher-order Padé (4FDHP) method is then derived. The Leontovich impedance boundary for the 4FDHP method and boundary for the 2 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{nd}$</tex-math></inline-formula> -order FD and higher-order Padé (2FDHP) method are also derived. The important problem of the propagation angle of the different approximations for the 3D-PE is investigated. Simulated results show that the proposed 4FDHP method achieves a larger propagation angle and higher accuracy than those of the 2FDHP method and the Mitchell-Fairweather alternative-direction-implicit (MF-ADI) method.

Mathematical Modeling of the Amplitude, Angular, and Time Characteristics of Short Radio Waves in Slightly Oblique Sounding of the Ionosphere

The method of bicharacteristics is used to study the propagation of decameter radio waves in the ionosphere containing the E, F1, and F2 layers and a traveling ionospheric disturbance (TID) upon slightly oblique sounding with frequency-modulated signals. The propagation of both ordinary and extraordinary waves is considered, the ionograms are compared, and their relative shift is studied. The structure of ionograms in the vicinity of caustics, which appear at the reception point at frequencies reflected in the vicinity of the E layer and TID, is studied. The divergence of the ray flux at the point of radiation reception, which determines a decrease in the amplitude, is calculated.

Diffraction Theory of Propagation of High-Frequency Radio Waves in a Spherically Layered Ionospheric Radio Channel

Diffraction Theory of Propagation of High-Frequency Radio Waves in a Spherically Layered Ionospheric Radio Channel

Comparative analysis between ERA5 reanalysis data and MRR observation data at different altitudes for fall velocity and liquid water content

Continuous measurements of rainfall parameters are required for radio planning and flood management among others. However, due to the dearth of requisite infrastructure and expertise within the region, it is usually necessary to use satellite and reanalysis data. In this study, the performance of ECMWF ERA5 data in providing fall velocity (W) and liquid water content (LWC) estimates at different altitudes was compared with measurements from a ground-based Micro Rain Radar in a tropical location. Results obtained showed correlation values of 0.60–0.94 and 0.16–0.93 for fall velocity and liquid water content, respectively. The performance of ERA5 was found to decrease with altitude. In general, the results show the sufficient reliability of the ERA-5 reanalysis data for the two parameters on vertical scales. Therefore, it can be inferred that the ERA-5 data are reliable in estimating the average LWC and W, especially on a vertical scale for both hydrological and radio wave propagation studies.

Analytical Comparison of Path Loss Models for Radio Wave Propagation over Yenagoa–Southern Nigeria

Using propagation models helps with communication system planning and maximizes the use of the radio spectrum, a limited natural resource. Here is a comparative analysis between some propagation models and actual measurements from Yenagoa, Southern Nigeria. Electric field strength measurements made during drive tests for two television transmitters operating at 210.25 MHz and 577.10 MHz make up the experimental data. Analytical comparisons were made between verified predictions for the free space, Okumura, and Hata models and measured data. The results demonstrate that these empirical models fail to take into account Yenagoa's actual terrain profile for television broadcast. The Okumura model is the best fit, with ideal values for root mean square error (RMSE) of 34.9136 and 33.2841 and average relative error of 0.13212 and 0.4327 for 210.25 MHz and 577.10 MHz, respectively. However, if the Okumura model is tailored for Yenagoa to improve electric field strength prediction and coverage estimation, better results can be attained.

Space–Time Structures in the Auroral Oval: Approaches to Modeling

The interaction of the magnetospheric–ionospheric (MI) system surrounding the Earth with the environment (solar wind) occurs in the form of a series of transient processes at different scales. The largest of them, magnetic storms, are obviously triggered by disturbances in the solar wind (direct driving). The role of the internal dynamics of the MI system, which is caused to a large extent by the nonlinearity and temporal delays of the loading–unloading processes of energy and particle from the solar wind into the magnetosphere, becomes more significant at smaller scales (substorms, pseudobreakups, injections, and activations). A typical dynamic state of the MI system is characterized as self-organized criticality or turbulence, which are characterized by statistical scale invariance (scaling) in the fluctuation distributions of many characteristics. The dynamics of the MI system is projected into the region of the auroral oval, the very existence of which is due to this dynamics. The space–time structure of auroral disturbances largely reflects the structure of processes in the MI plasma. The description of this structure is important both for studying the fundamental study of plasma processes and for many topical applied problems related to the propagation of radio waves in the ionosphere and vital activity at high latitudes. The paper discusses approaches and developments for constructing a model of the space–time structure of the auroral oval, based on fractal and multifractal characteristics.

The Analysis and Verification of IMT-2000 Base Station Interference Characteristics in the FAST Radio Quiet Zone

In this study, we aim to analyze the electromagnetic interference (EMI) regarding the Five-hundred-meter Aperture Spherical radio Telescope (FAST) caused by base stations in the International Mobile Telecommunications-2000 (IMT-2000) frequency band. By analyzing the frequency bands used by the transmitting and receiving devices and the surrounding environmental parameters and utilizing an approach to predicting radio wave propagation loss that is based on deterministic methods, we conclude by comparing the predicted received power at the FAST with its interference protection threshold. Our analysis demonstrates that, currently, only 55.31% of IMT-2000 base stations in the FAST radio quiet zone (RQZ) meet the protection threshold. Additionally, this article verifies the applicability and accuracy of the radio wave propagation model used in the research based on field strength measurements. Overall, this study provides valuable insights for improving the electromagnetic environment surrounding FAST and reducing the EMI caused by mobile communication base stations. It also provides corresponding analysis methods and useful suggestions for analyzing electromagnetic radiation interference in other radio telescopes.

Perturbations in the characteristics of ionospheric HF radio waves during the April 11, 2019, earthquake in Japan: Results from oblique sounding

The Harbin Engineering University HF software-defined radio system since 2018 continuously monitors dynamic processes launched in the ionosphere by energetic events in the Sun–interplanetary-medium–magnetosphere–ionosphere–subsystem coupling. The data collected during the submarine magnitude 6.0 earthquake that occurred off the East coast of Honshu, Japan, on April 11, 2019, have been analyzed with the specific objectives of determining the ionospheric response to the earthquake, the distortions of the radio-wave propagation channels, and identifying possible mechanisms for the transport of the disturbances at 845–2,260 km great-circle distances between the epicenter and the propagation path midpoints. Despite the ionospheric responses to powerful earthquakes have been studied since 1964, the problem of deriving global specifications of the disturbances remains pressing. The effects that the ionospheric disturbances from earthquakes have on radar, communications channels, radio navigation, radio astronomy, etc., are a matter of even greater urgency. The multiple path multifrequency radio system for sounding the ionosphere at oblique incidence provides a convenient tool for diagnosing such HF radio-wave propagation problems, acquiring a database containing the complex amplitudes of the signals and used to produce a sequence of Doppler spectra, for the first time, at a rate of 480 spectra per 1 h along 14 radio-wave propagation paths simultaneously with a 7.5-s temporal resolution and 0.02-Hz Doppler resolution over 20-s intervals. Analysis of the Doppler spectra, Doppler shift along the main ray, and signal amplitudes on the day when the earthquake occurred and on quiet time reference days showed that after the earthquake the Doppler spectra exhibit essential broadening, the Doppler shift along the main ray undergoes alternating sign Doppler variations, as well as quasi-sinusoidal variations with 3–5- and 10–20-min periods pertaining to the infrasound and atmospheric gravity wave frequency bands. The relative amplitudes of disturbances in the electron density are estimated to be ∼1% and 2–19% in the fields of infrasound of atmospheric gravity waves, respectively.

Unsupervised Clustering and Supervised Machine Learning for Lightning Classification: Application to Identifying EIPs for Ground‐Based TGF Detection

AbstractWe developed a framework merging unsupervised and supervised machine learning to classify lightning radio signals, and applied it to the possible detection of terrestrial gamma‐ray flashes (TGFs). Recent studies have established a tight connection between energetic in‐cloud pulses (EIPs, &gt;150 kA) and a subset of TGFs, enabling continuous and large‐scale ground‐based TGF detection. However, even with a high peak current threshold, it is time‐consuming to manually search for EIPs in a background of many non‐EIP events, and it becomes even more difficult when a lower peak current threshold is used. Machine learning classifiers are an effective tool. Beginning with unsupervised learning, spectral clustering is performed on the low‐dimensional features extracted by an autoencoder from raw radio waveforms, showing that +EIPs naturally constitute a distinct class of waveform and 6%–7% of the total population. The clustering results are used to form a labeled data set (∼10,000 events) to further train supervised convolutional neural network (CNN) that targets for +EIPs. Our CNN models identify on average 95.2% of true +EIPs with accuracy up to 98.7%, representing a powerful tool for +EIP classification. The pretrained CNN classifier is further applied to identify lower peak current EIPs (LEIPs, &gt;50 kA) from a larger data set (∼30,000 events). Among 10 LEIPs coincident with Fermi TGF observations, 2 previously reported TGFs and 2 unreported but suspected TGFs are found, while the majority are not associated with detectable TGFs. In addition, unsupervised clustering is found to reflect characteristics of the ionosphere reflection height and its effect on radio wave propagation.

Space–Time Structures in the Auroral Oval: Approaches to Modeling

The interaction of the magnetospheric–ionospheric (MI) system surrounding the Earth with the environment (solar wind) occurs in the form of a series of transient processes at different scales. The largest of them, magnetic storms, are obviously triggered by disturbances in the solar wind (direct driving). The role of the internal dynamics of the MI system, which is caused to a large extent by the nonlinearity and temporal delays of the loading–unloading processes of energy and particle from the solar wind into the magnetosphere, becomes more significant at smaller scales (substorms, pseudobreakups, injections, and activations). A typical dynamic state of the MI system is characterized as self-organized criticality or turbulence, which are characterized by statistical scale invariance (scaling) in the fluctuation distributions of many characteristics. The dynamics of the MI system is projected into the region of the auroral oval, the very existence of which is due to this dynamics. The space–time structure of auroral disturbances largely reflects the structure of processes in the MI plasma. The description of this structure is important both for studying the fundamental study of plasma processes and for many topical applied problems related to the propagation of radio waves in the ionosphere and vital activity at high latitudes. The paper discusses approaches and developments for constructing a model of the space–time structure of the auroral oval, based on fractal and multifractal characteristics.

Estimation of rain attenuation effect on radio wave propagation for broadband communication over northern Nigeria.

Rain induced effect on propagated signal was studied in this work. The weather parameters of two (2) locations representing two (2) climate zones in Northern Nigeria were employed, using the International Telecommunications Union (ITU-R P.618) rain attenuation model, to investigate the rain effect on strength of propagated signal ranging from Ku-band to V-band of the communication spectrum. The weather data were obtained from the Nigerian Meteorological Agency (NIMET) for a period of 10years (2009-2018) and assimilated into the model using 1-minute integration time rain rate. An elevation angle of 42.5°, which is the conventional elevation angle of systems to NIGCOMSAT-1R over the Atlantic Ocean region, was used. The results showed that annual rainfall amounts trends varied slightly with the different locations and climate zones, having 2018 and 2010 as the highest rain years within the studied years at Maiduguri and Sokoto respectively. Also, the difference between maximum and minimum 0.01% attenuation for the two locations are 2dB-3dB, 3dB-6dB for horizontal polarization and 1dB-1.5dB and 2dB-4dB for vertical polarization respectively at the two locations respectively. Rain attenuation can be managed well for propagated Ku-band signal with sophisticated sensors but above Ku-band, signal strength attenuation induced by rain could be really alarming.

The Refractive Effect of k-Factor on Radio Propagation over Lokoja, Nigeria

The effective earth radius factor (k-factor) has a refractive propagation effect on transmitted radio signals thus making its study necessary for the proper planning of terrestrial radio links and power budget. This study was carried out over the city of Lokoja, Nigeria, using ten years (2011 to 2020) atmospheric data of temperature, pressure and humidity both at the surface (12 m) and at 100 m AGL. The data were retrieved from European Centre for Medium-Range Weather Forecasts (ECMWF) ERA5. The k-factor yearly variation follows the same trend with minimum and maximum values obtained during dry and wet season months respectively. In addition, the highest mean value of 1.00042 was recorded in the month of August while the lowest value of 1.00040 was recorded in the month of January with an overall mean value of 1.0003. This value is less than the recommended standard of 1.33 by ITU-R. The propagation effect corresponding to k &lt; 1.33 is sub-refractive. The implication of this on radio wave propagation, especially terrestrial communications is that transmitted wireless signal is prone to losses. This can be mitigated through an effective power budget: Choice of transmitting antenna’s height and gain, so as to improve the Quality of Service over the study area.

Climatology of HF Propagation Characteristics at Very High Latitudes From SuperDARN Observations

AbstractConventional forecasting of high‐frequency (HF, 3–30 MHz) radio wave propagation is based on a combination of ionospheric and propagation models. However, at very high latitudes this approach is seriously undermined by the intrinsically dynamic ionospheric conditions regularly perturbed by energetic particle precipitations and strong electric fields. From this perspective, the multi‐year observations of HF propagation characteristics by Super Dual Auroral Radar Network (SuperDARN) radars across auroral and polar cap regions represent a unique opportunity for systematic validation of the conventional approach, as well as for creating an empirical propagation model directly from the radar observations. Qualitative identification and quantitative characterization of the propagation modes requires an accurate knowledge of the vertical angle of arrival (elevation angle) across the high‐latitude part of the radar network. This information has become available only in recent years, facilitated by the development of reliable data‐based calibration techniques for SuperDARN interferometry. We present the solar‐cycle/seasonal/diurnal climatology of HF propagation characteristics at very high latitudes derived from two‐frequency observations by the Rankin Inlet SuperDARN radar.

Influence of the Heterogeneity of Spatial Distribution of Peripheral Radio Equipment of 4G/5G Networks on the Level of Electromagnetic Background Created in Buildings

Known results of studies of the radio frequency electromagnetic background generated in buildings by electromagnetic radiation from the peripheral equipment of 4G/5G mobile communications , including equipment for massive machine-type communication /Internet of things ( mMTC / IoT ) and user’s devices for wireless telephony and data transmission , are based on the use of a model of uniform random distribution of this equipment over the building internal space . The adequacy of this model for the analysis of a number of 4G/5G scenarios is questioned due to the fact that , excluding user’s devices , the main part of the mMTC / IoT peripheral radio equipment located in buildings is distributed along the walls of the premises with a tendency to concentrate them near the intersections of flat surfaces of walls , floors and ceilings . Paper presents the results of comparative estimates of the average intensity of electromagnetic background inside building for different types of distribution of the set of point sources of RF electromagnetic fields over the building interior space : for their uniform distribution over internal space and for two types of heterogeneity of this distribution : for uniform distribution of sources over building internal surfaces and with their uniform distribution along the lines of intersection of these surfaces . Results of this analysis indicate a relatively small effect of the considered types of heterogeneity in the spatial distribution of radiation sources on the estimates of the electromagnetic background average intensity created by these sources inside the building , when using a technique based on the representation of the internal space of a building as a set of solid angles , which internal space separate sections are characterized by the constancy of the sources average space density and by the average conditions for radio waves propagation in the direction of the observation point .

Efficient physics‐based recurrent neural network model for radio wave propagation in tunnels at 2.4 GHz

AbstractThe vector parabolic equation (VPE) method has been widely applied to the modelling of radio wave propagation in tunnel environments. However, dense spatial discretizations are generally required for VPE simulations to achieve acceptable accuracy. This results in high computational costs for large‐size tunnels and high‐frequency wireless systems. This letter presents an efficient physics‐based recurrent neural network (RNN) model for modeling radio wave propagation in tunnels. The proposed RNN‐based model can leverage coarse‐mesh VPE to generate high‐fidelity received signal strength and achieve significant computational savings. The validity of the proposed approach is demonstrated against fine‐mesh VPE simulations in various tunnel cases.

Effects of Fire Plumes From Pine Needles on Small-Scale Fading in Radiowave Propagation

In this article, radiowave fading caused by fire plumes due to the burning of heaps of pine needles is studied. Detailed characterization of the fire impact in terms of excess loss due to the yielded plumes at UHF frequencies, mainly in the L-band, when considering two different ignition sources, is also presented. The implemented small-scale fire scenario is composed of a 1 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times 1$ </tex-math></inline-formula> m metallic grid covered with a 0.6 kg pine needle fuel bed that was placed right above a circular and linear gas burner to mimic an underbrush scenario. The propagation phenomena were evaluated through specific wideband measurements as the fire developed while intersecting the radio path at the antennas’ boresight. Results demonstrate changes in the propagation medium that is strongly influenced by the plume, which ultimately becomes (partly) ionized. Deep fades of up to 12 dB below median levels at specific frequencies during a short period of time, when the fire is more intense, were measured. We also obtained an overall median excess loss due to fire of up to 2 dB in the frequency range from 0.6 to 2 GHz in a relatively short path (below 1 m). A time-domain analysis allowed us to expand these results yielding fading values of the direct component of more than 3 dB in the presence of fire. Extending the findings presented in this article to a real-scale fire scenario, in which median excess loss of more than 20 dB and deeper nulls are ought to be expected, sets the rationale and motivation to pursue future work on the topic, with practical relevance to future mission-critical communication networks planning, such as, but not limited to, LTE Public-Safety and specific 5G use cases.

CNN‐based received signal strength prediction: A frequency conversion scheme

AbstractTo support the design and deployment of emerging high‐frequency wireless systems in various applications such as intelligent transportation, advanced received signal strength (RSS) simulation tools for radio coverage prediction are needed. In railway transportation, the vector parabolic equation (VPE) method is a commonly used approach for radio wave propagation modelling in large guiding structures such as tunnels. However, running VPE simulations at high frequencies in such an environment is computationally expensive, as the discretization parameters are closely related to the wavelength. In this letter, the authors propose a convolutional neural network‐based model that can efficiently provide RSS prediction at high frequencies by leveraging data obtained from VPE simulations at a lower frequency as an anchor. This proposed model can significantly improve the efficiency of VPE for high‐frequency RSS predictions and has been validated against conventional VPE in various tunnel cases.

Design, Analysis and Simulation of Microstrip Antenna Arrays with Flexible Substrate in Different Frequency, for Use in UAV-Assisted Marine Communications

The maritime land–sea communication channel experiences multipath shadowing and fading due to ships, onshore and offshore structures, and reflections from the sea surface. When using low altitude antennas, the sea surface itself can block the propagation of radio waves when the first Fresnel zone is obstructed. The latter can occur within a few kilometres of the transmitter at microwave frequencies. Sea reflections are stronger than ground reflections due to the higher conductivity of the sea, leading to more interference problems. In this paper, a microwave frequency patch antenna array is analysed, designed, and simulated for a novel system to improve marine communications to be applied by unmanned aerial vehicles (UAVs). The patch antenna array with flexible substrate will be studied with different frequencies. In this way, the test will check and obtain the best characteristics for an antenna that is built into the UAV with CTS studio.

An Iterative High-Accuracy ADI Method for the 3D Parabolic Equation

The alternating direction implicit parabolic equation (ADI-PE) method and the Crank–Nicolson parabolic equation (CN-PE) method have been widely used for solving the 3D parabolic equation (3D-PE) in radio wave propagation. The ADI-PE method is more computationally efficient than the CN-PE method. The accuracy of the ADI-PE method is improved by the higher-order Mitchell–Fairweather (MF)-ADI method. This paper presents an iterative high-accuracy (IHA)-ADI method for the 3D parabolic equation. A derivation of the proposed method is presented. The convergence and stability of the proposed method are estimated. Several numerical examples are considered to illustrate the advantages of the proposed method. The results of error analysis and a comparative study show that the proposed method is unconditionally stable and computationally efficient. The proposed method is more numerically accurate than the MF-ADI method.

Electronic Spectroscopy of Jet-Cooled NdO

Chemi-ionization reactions of the type M + O → MO+ + e- (M = Nd or Sm) are currently being investigated as a method to artificially increase the electron density in the ionosphere for control of micro- and radio wave propagation. Experiments involving the release of atomic Nd into the upper atmosphere have resulted in the production of a cloud that, on excitation by solar radiation, emits green light. It has been assumed that NdO was the carrier of this emission, but the existing spectroscopic data needed for this attribution is lacking. While the electronic spectrum of NdO has been well-characterized at wavelengths greater than 590 nm, relatively little spectroscopic data exist for emission wavelengths in the blue-green spectral range. In this study, spectra for jet-cooled NdO were recorded over the range 15,500-21,000 cm-1. Rotationally resolved laser induced fluorescence and vibronically resolved dispersed laser-induced fluorescence spectra were recorded, and nine new electronically excited states were identified. The data indicate that the electronic spectrum of NdO has relatively few allowed transitions in the green spectral range, casting doubt on the assignment of the Nd high-altitude release cloud green emission to NdO.