Efficient Preprocessed Ray Tracing for 5G Mobile Transmitter Scenarios in Urban Microcellular Environments

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.

The wide-angle parabolic equation gives a rigorous solution to the problem of diffraction by several buildings of arbitrary shape. Applications to propagation in urban microcellular environments are presented.

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.

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.

Autonomuous transportation systems require navigation performance with a high level of integrity. As Global Navigation Satellite System (GNSS) real-time kinematic (RTK) solutions are needed to ensure lane level accuracy of the whole system, these solutions should be trustworthy, which is often not the case in urban environments. Thus, the prediction of integrity for specific routes or trajectories is of interest. The carrier-to-noise density ratio (C/N0) reported by the GNSS receiver offers important insights into the signal quality, the carrier phase availability and subsequently the RTK solution integrity. The ultimate goal of this research is to investigate the predictability of the GNSS signal strength. Using a ray-tracing algorithm together with known satellite positions and 3D building models, not only the satellite visibility but also the GNSS signal propagation conditions at waypoints along an intended route are computed. Including antenna gain, free-space propagation as well as reflection and diffraction at surfaces and vegetation, the predicted C/N0 is compared to that recorded by an Septentrio Altus receiver during an experiment in an urban environment in Hannover. Although the actual gain pattern of the receiving antenna was unknown, good agreements were found with small offsets between measured and predicted C/N0.

International Reference Ionosphere and ray tracing algorithm are discussed in the paper. Three-dimensional real-time ray tracing method is illustrated In accordance with International Reference Ionosphere, ray tracing equations are resolved by Runge-Kutta method. Based on International Reference Ionosphere and ray tracing algorithm, the three-dimensional ray tracing simulation software is presented. The three-dimensional ray trace and the group path are estimated by the simulation software. The effectiveness and accuracy of the simulation results are verified by comparing with the experimental results.

In today’s workplace, the personal computer and spreadsheet have become commonplace, while lens design software, often costing more than the computer, is not. Any one of the generic spreadsheet programs can be an effective ray tracing tool. Anyone who has developed ray tracing software has found that the input/output problem can often be more difficult than the algorithms for ray tracing. The advancement in today’s spreadsheets has eliminated the need for sophisticated programming skills to produce usable ray tracing functions. The worksheet developed combines third-order ray tracing with aproximate polarization equations. Useful graphic functions can be developed for displaying the third-order surface contributions and the polarization change for each surface. Examples of the macros developed are shown. A demonstration of a double Gauss ray trace is given. These macros can also be a useful tool for those with high powered lens design software. The macros are designed so that a lens can be set up in the spreadsheet and used as the input to commercially available lens design software.

This paper presents the postprocessing results of a dual-polarized multiple-input-multiple-output (MIMO) channel measurement campaign, investigating two land mobile satellite link scenarios in urban environments. Basic channel evaluation metrics are examined to facilitate the selection of the appropriate communication technique. The ergodic channel capacity is found between 4.1 and 6.1 b/s/Hz and varies significantly with the elevation angle. The capacity is highly correlated with the terminal trajectory and signal reception. The cross-polarization discrimination (XPD) is found between 14.2 and 22.5 dB, whereas the cross-polarization isolation (XPI) is found between 12.8 and 21 dB, respectively. Furthermore, the correlation statistics and channel capacities are well approximated by existing stochastic channel models. Finally, from the channel stationarity analysis, large stationarity regions are found, the existence of which is also correlated with the terminal trajectory. The mean quasi-stationarity time is found between 41 and 66 s for different environments.

A fast 3-D ray tracing propagation prediction model based on virtual source tree is presented in this paper, whose theoretical foundations are geometrical optics(GO) and the uniform theory of diffraction(UTD). In terms of typical single room indoor scene, taking the geometrical and electromagnetic information into account, some acceleration techniques are adopted to raise the efficiency of the ray tracing algorithm. The simulation results indicate that the runtime of the ray tracing algorithm will sharply increase when the number of the objects in the single room is large enough. Therefore, GPU acceleration technology is used to solve that problem. As is known to all, GPU is good at calculation operation rather than logical judgment, so that tens of thousands of threads in CUDA programs are able to calculate at the same time, in order to achieve massively parallel acceleration. Finally, a typical single room with several objects is simulated by using the serial ray tracing algorithm and the parallel one respectively. It can be found easily from the results that compared with the serial algorithm, the GPU-based one can achieve greater efficiency.

In this contribution, possibility of using the backward ray tracing (RT) coupled with the finite-difference timedomain (FDTD) method for two-dimensional (2-D) simulations of the wave propagation in urban environments is demonstrated. For increased accuracy of exposure-assessment simulations, the FDTD method is used in small domains including inhomogeneous scatterers, whereas RT is used to simulate the wave propagation between these domains and buildings in urban environment. In this approach, contrary to the forward RT, many rays are generated for each diffracted ray and contributions from each receiver-transmitter path finally provide an excitation for the FDTD domains. A heuristic model of diffraction based on the uniform theory of diffraction has been used in the developed code. For the sake of simplicity, the method is presented in 2-D.

A high speed 'image-based' ray tracing algorithm is presented that applies to both indoor and microcellular environments. The building database and image generation operates in two dimensions. However, for each 2D path, all the corresponding rays are calculated in 3D including multiple floor-ceiling reflections for the indoor case and the extra ground reflection for the outdoor scenario. The field calculation is implemented using dimensional vector analysis with each ray considered separately. To show the practicality of such models, the ray tracing engine has been used to investigate a microcellular environment in the centre of Bristol. The speed and complexity of the resulting model is investigated as a function of the number of reflection, transmission and diffraction generations.

In this paper we modified the reflection coefficient of electromagnetic wave incident on the wall of buildings or obstacles that occurs in the mobile communication path by solving the nonlinear Riccati equations. For this purpose, the building walls are assumed to be inhomogeneous layers of brick and concrete where permittivity changes as a function of the wall thickness. Based on reflection coefficient modification, we proposed a new propagation model using uniform geometrical theory of diffraction (UTD) and geometrical theory of diffraction (GTD) for multiple diffraction paths in cellular mobile radio communication, and calculate the diffraction loss as well as the path loss for a row of buildings with two inhomogeneous faces. The measured reflection coefficient and diffraction loss are then compared to the theoretical results obtained from the proposed model. Our observations reveal good agreement between measurement data and theoretical results. Therefore it can be concluded that the modified reflection coefficient can adequately predict the reflective properties of the wall surfaces with different dielectric properties. So the modified reflection coefficient as well as the new UTD model can directly be applied for field estimation or diffraction loss calculation, as well as multipath signal strength or delay prediction in ray tracing algorithms used in mobile communication, radar, and radio links.

Ray tracing is a frequently used method for acoustic simulations, valued for its calculation speed and ease of use. Although it is fast, there are no fully ray tracing-based real-time simulation methods or engines. Under real-time restrictions, ray tracing simulations lose precision and the variance inherent in the random simulation method has too much impact on the outcome. In this paper, an algorithm called iterative ray tracing is presented that reduces the negative effects of real-time restrictions by iteratively improving the initial calculation and increasing the precision over time. In addition, new estimates of the expected value and variance of ray tracing simulations are presented and used to show the iteration steps in the new algorithm reduce variance, while maintaining the expected value. Simulations using iterative ray tracing are compared to measurements and simulations using the classical ray tracing method, and it is shown that iterative ray tracing can be used to improve precision over time. Although more testing is needed, iterative ray tracing can be used to extend most ray tracing algorithms, in order to decrease the adverse effects of real-time restrictions.

In an urban environment, radio wave interaction with buildings may affect considerably the propagation of radio waves, mainly because of multipath, diffraction, and shadowing effects. This paper outlines the effect of two-dimensional (2-D) (vertical and lateral) diffraction and compares a Fresnel-Kirchhoff scalar approach to a vectorial geometrical theory of diffraction (GTD) approach applied to a four-ray system. The former can be considered as a generalization of conventional knife-edge diffraction theory while the latter (GTD) is useful in the context of ray tracing. A very good agreement between the Fresnel-Kirchhoff and GTD results is found within the limits of validity of both methods. Moreover, it is shown that conventional knife-edge diffraction theory can largely overestimate attenuation (10-15 dB) behind tall buildings in the center of a city environment. Different frequency bands have been tested for the sake of comparison, and emphasis has been put on the radio communications frequency bands used for the global system for mobile communications (GSM) and DCS/DECT systems at 900 and 1800 MHz.

Almost all current games are implemented using the graphics processing units (GPUs) found on almost every PC. These GPUs use the z-buffer algorithm to do visibility calculations. Ray tracing, an alternative to the z-buffer algorithm, delivers higher visual quality than the z-buffer algorithm but has historically been too slow for interactive use. However, ray tracing has benefitted from improvements in computer hardware, and many believe it will replace the z-buffer algorithm as the visibility engine in games. If that replacement happens, it will imply fundamental changes in both the API to and capabilities of 3D graphics engines. This paper discusses the implications for games and graphics oriented classes should this switch to ray tracing occur.