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In the design and optimisation of marine wireless communication and navigation systems, a thorough investigation of radio wave propagation characteristics under atmospheric ducting conditions is essential. The authors aim to enhance the efficiency of radio wave propagation loss prediction in marine atmospheric ducting environments, proposing a prediction model based on Fast Reordered‐Alternate Direction Decomposition (FR‐ADD). By approximating the diffraction term into three independent components, exploiting the commutative properties of the Fourier transform to reduce the spatial dimensions, and incorporating a rapid algorithm for the parabolic equation, the model optimises the stepping process and significantly improves computational efficiency. Simulation experiments demonstrate that, in the long‐distance and complex marine ducting environments, the model not only maintains prediction accuracy but also substantially reduces computational load and prediction time, effectively realising over‐the‐horizon propagation prediction. In the experiment of radio wave propagation characteristics in the Yellow and Bohai Seas, the simulation data from the FR‐ADD model showed significant correlation with actual measurements and simulations from the AREPS software, confirming the method's efficiency and practicality. [ABSTRACT FROM AUTHOR]

Propagation models are essential for the prediction of received signal strength and the planning of wireless systems in a given environment. The vector parabolic equation (VPE) method has been widely applied to the modelling of radio wave propagation in tunnels. However, carrying out simulations for large‐scale environments is still computationally expensive. A convolutional neural network (CNN)‐based propagation model, which can provide high‐fidelity received signal strength prediction based on results from low‐cost VPE simulations, is proposed. A thorough study of the generalisability, including both interpolation and extrapolation capabilities, of the proposed CNN model is conducted. It is found that the proposed model can achieve significant computational savings while maintaining acceptable accuracy, and its performance is validated in both simulations and actual tunnel cases. [ABSTRACT FROM AUTHOR]

Radio wave propagation modelling in railway environments is of fundamental importance in designing reliable train communication systems. Parabolic equation (PE) methods have been widely applied to the modelling of wave propagation in tunnels due to their high computational efficiency and fidelity. The finite-difference parabolic equation (FDPE) and the split-step parabolic equation (SSPE) methods are two commonly used approaches to solve PE numerically. However, the relevant literature is still missing a comprehensive study of their performance, including the selection of parameters such as discretisation steps and the tradeoffs involved in terms of their accuracy and efficiency, especially as current wireless systems shift to high frequencies. In this study, a systematic analysis of the error and computational complexity of the FDPE and SSPE methods for radio wave propagation modelling in tunnels is provided. Guidelines for the choice of their parameters are provided, and their performance is demonstrated through both numerical examples and experimental measurements in actual tunnel cases. [ABSTRACT FROM AUTHOR]

Accurate radio wave prediction models are necessary for the innovation of mobile communication technology and the deployment of wireless sensor networks in railways. The parabolic wave equation (PWE) method is one commonly used method to predict the electromagnetic characteristic of long railway tunnels. However, the advent of novel antennas and technologies (e.g., beam steering, beamforming) has posed new challenges to PWE‐based models such as effective means of taking tilted beam patterns into account. This study addresses such a challenge by using tilted Gaussian beams to embed antennas with oriented patterns or tilted beam directions into PWE‐based models. The proposed approach does not reduce the simulation efficiency of PWE itself. The validity and practicability of the technique are demonstrated by comparing against ray‐tracing as well as experimental measurements in various tunnel environments. [ABSTRACT FROM AUTHOR]

In an urban built city environment, the performance of electromagnetic (EM) wave propagation through building materials poses a new set of challenges to radio frequency engineers in the prediction of the 5G‐network coverage planning. We propose the prospects on the use of composite building materials enhanced with different volumetric fractions of iron (III) oxide (Fe2O3) inclusions as a reddish‐brown colouring admixture in modern‐day concrete. Using a non‐destructive microwave measurement technique, a two‐factor 6 × 10 factorial experiment and a randomized controlled statistical study from 3.40 to 3.60 GHz is conducted on 15‐cm thick building material prototypes enhanced with 2‐wt% to 10‐wt% micro‐sized Fe2O3 inclusions to evaluate their efficacy on EM wave propagation. Transmission coefficients (S21) data are analysed statistically between treatment and control groups, yielding up to 2.28 dB mean S21 improvement in performance and a fractional bandwidth of 100% by the 2‐wt% Fe2O3 treatment group. Electromagnetic characterisations of the fabricated mortar samples with different Fe2O3 inclusions are performed using Nicholson‐Ross‐Weir model followed by the evaluation of dielectric and propagation losses. Our findings support the use of 2‐wt% Fe2O3 as the optimal volumetric fraction which improves the microwave transparency, thus creating potential EM benefits for the fifth‐generation (5G) wireless communication systems. [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]

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]

This contribution presents propagation measurements at 60 GHz in indoor non-line of sight scenarios. Besides analysing the measurements, the authors have considered several system aspects, such as bandwidth and directivity in order to investigate the small-scale behaviour of the radio channel after beam-forming. The results show that due to the high resolution in the angular and time domain achievable by large antenna arrays and wideband signals, the fading is significantly reduced and the equivalent transmission channel becomes more sparse and deterministic. These insights represent an essential source of information for future systems design and the ongoing channel modelling activities for systems operating at mm-waves. [ABSTRACT FROM AUTHOR]

In spherical near-field (NF) measurements, post-processing techniques based on spatial filtering have been presented as an interesting tool for the mitigation of echoes or stray signals deriving from the environment surrounding the antenna under test (AUT). The spatial filtering is very efficient in measurement scenarios with a stationary AUT. Whenever the AUT is rotating, in order to increase the effectiveness of the echo reduction, the antenna needs to be displaced outside the centre of rotation. Unfortunately, the number of acquisition samples needed to represent the AUT in offset configuration is higher with respect to one needed for the onset configuration. An innovative NF/far-field transformation algorithm for spherical offset measurements which allows to significantly reduce the number of measurement samples has been recently proposed. Such technique has been named translated spherical wave expansion (TSWE) and is based on the definition of new reference systems centred on the AUT rather than on the origin of the measurement sphere. In this study, the authors present the experimental investigation of the TSWE echo reduction properties for offset AUT. [ABSTRACT FROM AUTHOR]

In this study, the authors present a measurement-based analysis of the indoor radio channel characteristics of both the specular and dense multipath components [specular part of the channel (SMC) and diffuse part of the channel] at 94 GHz within a 3 GHz bandwidth. On the basis of an investigation of the frequency stationarity of this band, they have selected multiple sub-bands to perform their evaluation. A method is developed that allowed for the estimation of the specular propagation paths, after which the remainder is regarded as the diffuse spectrum. Radio channel characteristics such as the path loss, root-meansquare delay spread, and the SMC ratio have been calculated as a function of transmitter-receiver distance, and in the different sub-bands. On the basis of the diffuse spectrum, the behaviour of the reverberation time is analysed for the first time in the 94 GHz band. [ABSTRACT FROM AUTHOR]

An improved two-way parabolic equation (2WPE) method for predicting radio wave propagation in obstacle environment is proposed. Classical 2WPE is mainly utilised for calculating radio propagation under irregular terrain by taking the undulating ground and obstacles as a whole, which yields calculation precision is very limited by the terrain inclination. In order to address the above problems, according to the principle of domain decomposition, by dividing the obstacles and the ground into different zones, 2WPE can be improved to calculate the fields in obstacle environment. With the improved 2WPE, the real phases of both the forward and backward waves can be retrieved when a radio wave entering and leaving the obstacles, and the total field can be obtained by superposition of forward and backward waves. After that, method of moments (MoM) is applied to verify the accuracy of the improved 2WPE in the short distance. In the simulation, the equivalent source model is used to unify the initial field or source settings of 2WPE and MoM to improve the verification precision. The accuracy and superiority of the improved 2WPE are proved, which lays a foundation for the analysis of radio wave propagation in the more complex environment. [ABSTRACT FROM AUTHOR]

Millimeter wave (mmWave) and Terahertz (THz) technologies are the enabler of providing high-data rate communications for 'smart rail mobility'. In this paper, six scenario modules for mmWave and THz train-to-infrastructure channels are defined and constructed. All the main objects, such as tracks, stations, crossing bridges, tunnels, cuttings, barriers, pylons, buildings, vegetation, traffic signs, billboards, trains, etc., are modeled according to the typical geometries and materials in reality. The three-dimensional (3D) models of these six modules are publicly available and freely downloadable. Furthermore, extensive ray-tracing simulations in the 60 GHz band with 8 GHz bandwidth are made in all the six modules with two antenna setups. Path loss exponent, shadow factor, Ricean K-factor, root-mean-square (RMS) delay spread, and coherence bandwidth are extracted and analyzed. These channel characteristics show that the objects that might not be so impacting on lower frequency channels indeed influence mmWave channel properties, and therefore, they can even play a more important role in the channels at higher frequency bands - THz. The channel characteristics analyzed in this study provide the foundation for future work that aims to streamline the design, simulation, and development of mmWave and THz communications enabling smart rail mobility. [ABSTRACT FROM AUTHOR]

The performance of the satellite communication systems employing polarisation diversity or frequency-reuse schemes to improve the spectral efficiency is degraded due to the depolarisation-induced interference originated by raindrops and ice particles present along the Earth-Space propagation path. Two models account for both rain and ice contributions. One predicts the long-term cumulative distribution function (CDF) of cross-polarisation discrimination (XPD). The other predicts the relationship between XPD and co-polar attenuation (CPA) and it was derived considering exclusively data at the V-band. In this study, the former model is improved by considering the individual ice and rain contributions and their combined effects, while the latter is validated against new measurements at the Ka band. New models are then proposed for the XPD-CPA relationships at the Ka-band taking into account both rain and ice contributions and also their combined effects. Finally, the predictions provided by the first model are usually converted to the corresponding XPD-CPA relationship using the long-term first-order statistics of rain attenuation, (incorrectly) considering that the equiprobability hypothesis applies. A new approach for the conversion of the XPD CDF into the corresponding XPD-CPA relationship is presented. [ABSTRACT FROM AUTHOR]

Through investigating the phenomenon of amplitude-phase interaction, the authors present a detailed study on the propagation of signal with a sinusoidal envelope in dispersive systems. With respect to the pulse signal, the phase delay of the base-band signal was previously defined to characterise the frequency tone delay in the base-band signal spectrum. However, comparing the phase delay of the base-band signal with the group delay has enabled the physical meaning of the group delay to be clarified. Of particular relevance, they observe that the frequency tone delay with frequency tends to zero in the spectrum of the base-band signal, rather than the delay expected of a group of frequency tones. With this new definition in place, they developed a new method for the precise analysis of signal propagation, which importantly has a capacity to show details in relation to both the envelope distortion and the phase distortion of the carrier. [ABSTRACT FROM AUTHOR]

This study reports the results of an indoor propagation measurement campaign and channel characterisation at 11 and 14 GHz, which are the candidate bands for the future communication systems. The measurement procedure allows the characterisation of both the large- and small-scale statistics of line-of-sight (LOS) and non-LOS (NLOS) channels. Based on the measurements, a log-distance path loss model is proposed, and the root-mean-square (RMS) delay spread is discussed. A Nakagami distribution is found to well describe the statistics of the small-scale fading, by using Kolmogorov-Smirnov, Chisquare, and Anderson-Darling tests. A distance dependent linear model is proposed to predict the Nakagami m-parameter. In addition, the cross-correlations of these channel parameters are analysed based on measurements, and the cross-correlations between the shadow fading, RMS delay spread and m-factor can be clearly observed for LOS condition, whereas the obstruction of NLOS reduces the cross-correlations. [ABSTRACT FROM AUTHOR]

The study of electromagnetic wave propagation on human bodies in dynamic motion can yield valuable information toward the advancement of wireless body area network technology. A human body model and simulation methodology is presented that simulates loss between on-body transmitting and receiving antennas during human motion activities. Experiments of human volunteers performing the motion activities complement the simulation approach. Motion capture data prescribes the model body position over simulated frames of the activity. Measured transmission data is used for comparison and validation of the simulations. [ABSTRACT FROM AUTHOR]

In this study, a simplified temperature-dependent expression of electron mean free path (MFP) is proposed first. Then, the electrical model of multi-walled carbon nanotube bundle-based through-silicon vias (MWCNTB-TSVs) is established considering the temperature effects of the MFP, metal-oxide-semiconductor capacitance, substrate conductance and number of conducting channels of MWCNT. Based on this model, the propagation constant, forward transmission coefficient S21 and crosstalk at different temperatures are calculated. By analysing the phase constant, the zero dispersion transmission condition is obtained. According to this condition, the guidelines on how to select the substrate in different level integrations are proposed. Furthermore, a concise formula for the equivalent conductivity of MWCNTB is proposed. Moreover, the minimum diameter of MWCNTB-TSV whose attenuation is less than that of copper-filled TSV has been deduced. [ABSTRACT FROM AUTHOR]

The eigenwave propagation problem is solved for a periodic waveguide composed of a planar dielectric waveguide and a reflecting diffraction grating. The technique the authors used is the spectral theory of open waveguide structures. The numerical data for the dependences of the propagation constants of surface and complex (leaky) eigenwaves are presented versus frequency and geometrical parameters of the periodic waveguide. In the frequency range of leaky eigenwaves, the angular-frequency characteristics of the radiation directivity are experimentally studied. The experimental results demonstrate the feasibility of the proposed approach. [ABSTRACT FROM AUTHOR]

The accurate prediction of radiowave coverage at high frequency-ultra high frequency over irregular terrain features is of importance in the design and development of low-cost and low-power communication systems. This study studies the problem of electromagnetic wave propagation, excited by a short dipole, above a dielectric ground plane with an arbitrary dielectric profile and an irregular interface. This investigation is a natural extension of the classical Sommerfeld problem with the exception of the random surface irregularities at the interface between the two dielectric media. It is assumed that the interface profile height variations are small compared with the wavelength. First, the bistatic scattering of a plane wave illuminating the rough surface is solved using a perturbation solution of an integral equation for the induced polarisation current. Analytical expressions for the coherent field and incoherent scattered power at an arbitrary observation point are obtained. Then, the solutions for the coherent and incoherent scattered power generated by a small dipole of arbitrary orientation and position are derived by expanding the field of the dipole in terms of a continuous spectrum of plane waves and using superposition. The effects of the rough interface on the surface waves and on depolarisation are studied. [ABSTRACT FROM AUTHOR]

This study presents an improved method of reactive loading for miniaturisation of coupled-line filters. Compared to the previous method, the proposed method requires a reduced number of reactive elements. Moreover, miniaturisation is accomplished with equal reactance. Effectively, this further decreases the number of reactive elements. Therefore apart from improved loss performance because of the reduced number of low-Q lumped elements, low-cost fabrication and simpler design procedure are also achieved while maintaining a similar rate of miniaturisation. A complete set of design equations is provided for both shunt-capacitive and series-inductive loading. The ideal simulation results, which are in excellent agreement with those of conventional counterparts based on λ/4 lines, theoretically validate the method, whereas the experimental results that match the ideal results better than the previous method demonstrate the practicality of the proposed method. [ABSTRACT FROM AUTHOR]

The tremendous growth of low power wireless technologies oriented to smart city applications has conduced to evaluate the propagation aspects under typical communication scenarios in urban environments where in contrast to cellular technologies the transmitter and or the receiver antenna can be deployed at different heights near ground. Thus, the authors introduce a unified empiric parametrised propagation model with validated parameters from the measurements to study the propagation characteristics in near-ground scenarios. The proposed model considers the antenna's height as well as external power losses because of objects that may block the line-of-sight to the receiver. The main results of this research demonstrate that in near-ground wireless links, the wireless range is severely reduced because of diffraction caused by ground. However, in scenarios where the receiver is always higher than the transmitter the diffraction is null and the path loss slope is less than free space, with the consequence of a considerably higher wireless range. The propagation model presented here is a valuable tool for network planning where typical cellular propagation models might not be appropriate. [ABSTRACT FROM AUTHOR]