Diffraction studies in urban environment with wide-angle parabolic equation method

Two-and-one-half dimensional ray tracing models, in combination with the uniform theory of diffraction and geometrical optics, are widely employed for propagation prediction in urban microcellular environments because of their high efficiency and reliable prediction accuracy. In this study, an improved ray tracing algorithm based on the “orientation face set” concept and on the improved 2D polar sweep algorithm is used. The aim of this paper is mainly to analyze the effects of different propagation mechanisms on ray-tracing-based coverage predictions in urban microcellular environments. In addition, the effects associated with the coverage prediction are visually represented.

There has been a great deal of interest in radio channel modeling for upcoming vehicular and device-to-device 5G applications. Site-specific models for such mobile transmitter scenarios become time-consuming as the visibility computations need to be independently performed for each transmitter location. This paper presents an efficient ray-tracing algorithm for a mobile transmitter radiating in an urban environment. The model presented uses a precomputed database of intravisibility of walls and edges in the environment. A visibility table that contains a list of walls and edges visible to multiple transmitters along a linear trajectory is computed for the given order of ray interaction. The walls and edges visible at a given location along the transmitter route are then readily determined using the visibility table thereby accelerating the ray-tracing algorithm. The validation results show considerable time-saving over unaccelerated ray tracing.

The frequency region 28-38 GHz has potential applications in fixed-wireless broadband services on account of availability of large spectrum and adequate device support to ease spectrum congestion problems, particularly in urban centers. This paper envisages development of a multiray propagation model to investigate multipath fading prevailing in millimeter wave radio propagation in a micro cellular environment. The model is simulated and measurements are carried out to estimate fast fading, propagation loss, and delay spread along micro cellular streets of variable width. The results depicted in the paper yields quantitative trends, with specific use in planning radio cells for fixed- wireless broadband services in urban microcellular environment.

The parabolic approximation to the wave equation is examined within the context of normal mode theory. In a layered waveguide, the horizontal propagation constants and modal amplitudes of the field Ψ satisfying the standard parabolic equation (SPE) approximation can be mapped exactly into the amplitudes and wave numbers of the normal modes for the field p satisfying the Helmholtz wave equation. However, this is not the case for certain other parabolic approximations, such as the wide-angle parabolic equation (WAPE) approximation. Approximate mode functions for the WAPE approximation are developed. These mode functions are then used to decompose range-independent sound-pressure fields computed using the WAPE approximation. The resulting modal coefficients and eigenfunctions obtained using the WAPE mode functions are compared with those obtained using standard normal mode theory.

Modern cellular communication networks are already being perturbed by large and steadily increasing mobile subscribers in high demand for better service quality. To constantly and reliably deploy and optimally manage such mobile cellular networks, the radio signal attenuation loss between the path lengths of a base transmitter and the mobile station receiver must be appropriately estimated. Although many log-distance-based linear models for path loss prediction in wireless cellular networks exist, radio frequency planning requires advanced non-linear models for more accurate predictive path loss estimation, particularly for complex microcellular environments. The precision of the conventional models on path loss prediction has been reported in several works, generally ranging from 8–12 dB in terms of Root Mean Square Error (RMSE), which is too high compared to the acceptable error limit between 0 and 6 dB. Toward this end, the need for near-precise machine learning-based path loss prediction models becomes imperative. This work develops a distinctive multi-layer perception (MLP) neural network-based path loss model with well-structured implementation network architecture, empowered with the grid search-based hyperparameter tuning method. The proposed model is designed for optimal path loss approximation between mobile station and base station. The hyperparameters examined include the neuron number, learning rate and hidden layers number. In detail, the developed MLP model prediction accuracy level using different learning and training algorithms with the tuned best values of the hyperparameters have been applied for extensive path loss experimental datasets. The experimental path loss data is acquired via a field drive test conducted over an operational 4G LTE network in an urban microcellular environment. The results were assessed using several first-order statistical performance indicators. The results show that prediction errors of the proposed MLP model compared favourably with measured data and were better than those obtained using conventional log-distance-based path loss models.

Detailed characterization of radio propagation channels is a major requirement for the successful design of mobile communication systems. In this paper, a mobile radio channel characterization process based on the FDTD method is presented. The merits and demerits of the currently used methods, namely the impulse-response method and ray-tracing methods, are briefly discussed. The total field formulation of the FDTD method is discussed. The simulation model consists of streets with concrete buildings. The received signals at the same LOS and OOS locations are presented.

This paper concentrates on the propagation loss of the rooftops of buildings in urban environment by using parabolic equation. The radio communication is direct to each subscriber, the prediction of signal strength is most important in urban environments where subscriber density is high, and the buildings have a profound influence on the propagation. Because of complexity of radio propagation theoretical prediction in built-up areas, and propagation must take place through the buildings or over the rooftops with the field diffracted at the roofs down to street level, what's more, the primary propagation path lies over the tops of the buildings. Therefore, we have mainly taken into account the propagation-loss of the building rooftops. In the paper, the rows of buildings in urban areas are modeled as a series of perfectly conducting rectangular plateau with the purpose of simplifying the model to facilitate the solution. In addition, we proposed four kinds of typical urban models. As we all know, a highly attractive and effective model for the prediction of electromagnetic-wave propagation effects above the Earth's surface is the split-step parabolic-equation (SSPE) method, which it requires less computing effort than full elliptic methods. In this paper, we applied it to predicate the propagation-loss of the rooftops of buildings in urban environments. The comparison between the parabolic equation prediction and experimental data of the various models are presented, and the results are very promising. It is proved that the parabolic equation is a powerful and accurate method to calculate the electromagnetic wave propagation.

We consider an urban fiber-optic microcellular environment in which a cigar-shaped cell consists of several microzones with their own antenna sites connected to a central station through optical fibers. To increase the efficiency of radio resources and to reduce unnecessary hand-off calls between microzones, we propose a movable safety zone scheme in which each communicating user has his own safety zone not permitting cochannel reuse. His safety zone also can move if his cochannel interference is not met as he moves to an adjacent microzone. Considering user mobility characteristics and urban microcell shapes, we analyze and evaluate the proposed system in terms of intercell/intracell hand-off rate, call blocking probability, and channel reuse parameter. The proposed system can handle a traffic capacity of about 12 Erlangs for 7 traffic channels under a call blocking probability of 1%, and generates a negligibly small number of intracell handoffs compared with intercell handoffs.

A double-layer model is proposed to reduce the calculation amounts of the Linear Ship Map (LSM) model. The proposed model can be used for rapid and accurate calculation of the electromagnetic propagation characteristics in the complicated atmospheric environment over the sea. In the proposed model, the calculation regions are divided into the upper-layer and the lower-layer. The upper-layer is calculated by the Wide angle Parabolic Equation (WPE) model and the lower-layer is calculated by the LSM model. Through reducing the calculation height and optimizing the step length, the proposed model can be exact and rapid. By simulation, the proposed model is compared with LSM model in the smooth and the rough sea surface conditions. The results show that the proposed model can decrease the calculation time by 1/10 in the rough sea surface condition.

Based on the conventional split-step Fourier transform(SSFT),the recursive two-way parabolic equation(TWPE) modeling is presented for the problems of former algorithms' deficiencies and computational error.The traditional algorithms forecast only forward-propagating waves and neglect the backward-propagating waves,which causes greater error in the presence of irregular terrain boundary environment.The new algorithm enhances the computation accuracy and remedies the insufficiencies by the recursive two-way split-step method.Compared to traditional wide-angle parabolic equation(WAPE) and geometrical theory of diffraction(GTD),the correctness and applicability of the model are verified by simulation results in the complex environment including single knife-edge,double knife-edges and real terrain.

Radar systems performance under anomalous propagation conditions can be predicted if the atmosphere is properly known. This article introduces a tomographic approach to estimate refractivity in the troposphere with an adjoint-based inversion method. A new adjoint model is developed for the 2-D wide-angle parabolic equation using a variational adjoint approach, to invert refractivity from phaseless data measured with an array of radio receivers in an open-sea environment. The obtained adjoint model is validated considering propagation through a range-independent medium over a flat perfectly-electric-conducting surface at horizontal polarization. The ill-posedness of the regarded inverse problem is shown with the optimization landscapes. The parametric study indicates the potential use of this method as a refractivity gradient retrieval system under certain circumstances.

Wind Turbine Noise (WTN) variability is often related to the influence of local micrometeorology as well as to space and time variations in the ground properties. Thus, the PIBE Project (2020-2024) aims to estimate these variabilities and their associated uncertainties. Its objective is to enable engineering companies or wind farm developers to estimate more accurately the risk of noise. In the WP2 of the PIBE project, 3 approaches are explored: (i) a NUMerical approach through the development of a metamodel, (ii) an EXPerimental approach through a major in-situ measurement campaign lasting more than 1 year, and (iii) a STATistical approach consisting in the evaluation of WTN variability. The NUM approach consists in sound emission calculation of each wind turbine using the Amiet's theory, and sound propagation calculation using a wide-angle Parabolic Equation (WAPE) modelling. The EXP part of the PIBE project has led to the development of a large database, accessible via a dedicated Shiny application. The last approach (STAT) has been carried out using both an open-access online tool called WindTUNE and an open-source tool based on Code_TYMPANTM, namely OCP. The 3 approaches (NUM + EXP + STAT) are presented and the corresponding results are discussed.

In this paper, perfectly absorbing thin screen is applied to the three-dimensional (3D) parabolic equation method in order to predict the propagation of electromagnetic waves in urban environments. The impedance boundary condition is used to represent the lossy nature of the ground and the Tukey window is adopted to attenuate the fields smoothly at the upper boundary without reflections. Besides, buildings are equivalent to a series of perfectly absorbing thin screens arranged along the direction of propagation and we use the split-step Fourier transform algorithm to solve the 3D parabolic equation. Finally, in order to validate the proposed method, several numerical simulations of a typical building on a flat ground are made and the results are compared with those in the literature. As a result, good agreements are observed.

The behavior of radio propagation in cross-polarization (X-pol) in urban environment is studied with the aid of both MIMO measurements and Ray Tracing simulation. Several microcellular scenarios are considered in the paper (LOS, NLOS, street corner), and the behavior of X-pol discrimination (XPD) as a function of the distance is analyzed. Results show that typical XPD values fall between 8 and 10 dBs, and are nearly independent of link distance.

A numerical method to solve 2D diffraction problems is used in this work to understand the number and placement of screens needed to represent individual buildings in path loss prediction tools. The methodology used to determine the field strength is based upon the Kirchhoff-Huygens integral, where the incident field on the plane containing a screen is given in terms of the field in the aperture plane of the previous screen. A relatively simple analysis is performed, whereby two different screen representations for the buildings between the transmitter and receiver are used to obtain the excess path loss over free space. The results clearly indicate that screen placement variability does not effect the path loss range dependence. The importance of representing a building by one or two screens has considerable consequences, namely whether on average, the predicted results are 4-7 dB off actual path loss values.