Conventional Ray Tracing Research Articles

Efficient Exclusion Strategy of Shadowed RIS in Dynamic Indoor Programmable Wireless Environments

Recent efforts have promoted programmable wireless environments (PWEs) to enhance the reception quality in high-frequency bands via reconfigurable intelligent surfaces (RISs). However, relevant research efforts are limited to setups with stationary users. This paper shows that crowd mobility in indoor PWEs induces spatio-temporal shadows on the surfaces, resulting in spatio-temporal sparsity in channel gains due to signal blockages. This overlooked aspect impacts the operation strategy of PWEs as the shadowed RIS tiles would contribute to the overheads while offering almost no improvement to the reception quality. Hence, this paper proposes an optimal strategy that excludes the shadowed tiles, which maximizes the utilization efficiency of RISs while minimizing the overheads. Since signal blockage is tied with the details of user mobility, a general model does not exist to identify such shadowed tiles for exclusion. Hence, we follow a data-driven approach that capitalizes on a realistic indoor mobility model and ray-tracing to generate the channel data. However, conventional ray-tracing presents high complexity that hinders data generation. So, we propose an approach to identify the shadow regions with a nine-order of magnitude reduction in complexity to efficiently generate the channel data. Furthermore, we present two exclusion strategies that offer guaranteed and best-effort quality-of-service support, and each can identify the tiles to be excluded via a search method with a complexity of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">O(N)</i> for <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> tiles. The results indicate that the proposed strategies reduce the overheads by 45 - 50% while maintaining optimal service quality in various environments, operation frequencies, and user and access point density.

On Dynamic Ray Tracing and Anticipative Channel Prediction for Dynamic Environments

Ray tracing algorithms, that can simulate multipath radio propagation in presence of geometric obstacles such as buildings, objects or vehicles, are becoming quite popular, due to the increasing availability of digital environment databases and high-performance computation platforms, such as multi-core computers and cloud computing services. When objects or vehicles are moving, which is the case of industrial or vehicular environments, multiple successive representations of the environment ("snapshots") and multiple ray tracing runs are often necessary, which require a great human effort and a great deal of computation resources. Recently, the Dynamic Ray Tracing (DRT) approach has been proposed to predict the multipath evolution within a given time lapse on the base of the current multipath geometry, assuming constant speeds and/or accelerations for moving objects, using analytical extrapolation formulas. This is done without re-running a full ray tracing for every "snapshot" of the environment, therefore with a great reduction in both human labour and computation time. When DRT is embedded in a mobile radio system and used in real-time, ahead-of-time (or anticipative) field prediction is possible that opens the way to interesting applications. In the present work, a full-3D DRT algorithm is presented that allows to account for multiple reflections, edge diffraction and diffuse scattering for the general case where moving objects can translate and rotate. For the purpose of validation, the model is first applied to some ideal cases and then to realistic cases where results are compared with conventional ray tracing simulation and measurements available in the literature.

Numerical feasibility study on signal discrimination in reflective environment of tungsten PFC

In the reflective environments of tungsten plasma facing components (PFCs), diagnostics of tokamaks will suffer from signal distortions since the reflectivity of tungsten PFCs are not negligible especially in the infrared (IR) range [1,2]. However, considering that most optical reflective systems are linear, it might be possible to eliminate the reflections if all ray information is provided. So, the possibility depends on the ray information of the system, and it can be derived using ray tracing simulations. For the feasibility study, the own ray tracing program of KFE has to be built since the conventional ray tracing programs have a limitation in providing full ray information. Among diagnostics, temperature measurement of PFCs is an issue for tungsten PFCs since it is a fundamental measurement for machine safety. So, as a feasibility study of signal discriminations, the emitted radiance was examined, and it has shown to be quite successful. This paper shows the possibility of reflection discrimination using ray path information.

Multiscale Optical Modeling of Perovskite-Si Tandem Solar Cells

With the success of silicon (Si) solar cell technology, research and development on higher efficiency multijunction solar cells is gaining much attention. Tandem cells with a perovskite top cell and a Si bottom cell show particular potential. However, the optical modeling of such devices is complicated by the broad range of length scales involved; the optically thin layers and nanoscale features of a perovskite solar cell require some version of wave optics or even full field electromagnetic (EM) calculations, while the micrometer scale structuring and large dimensions of Si cells are much more manageable using geometrical (ray) optics. In the present work, a method for combining EM and ray optical calculations is developed and described in detail, with examples provided in the software Comsol Multiphysics. For regions with thin films or nanoscale features, EM wave calculations are performed using the finite element method. These calculations provide the phase and amplitude of the waves diffracted into different orders, of which only the regular reflection and transmission are typically of relevance for nanoscale periodicity. In the ray optics simulation, the corresponding regions are implemented as diffracting interfaces, with deterministic transformations of the Stokes vector components according to the EM wave calculations. Meanwhile, the absorbed intensity of intersecting rays is recorded. The method is applied to separate perovskite and Si solar cells and to a few tandem solar cells of relevance for two- versus four-terminal configurations. Corrections for strongly absorbing media in the ray tracing algorithm, which use generalized versions of the Fresnel coefficients, Snell’s law and the Beer-Lambert law, are also evaluated. In a typical Si solar cell with a front surface structure of inverted pyramids, such corrections are found to reduce the absorption by up to 0.5 percentage units compared to a conventional ray tracing calculation. The difference is concluded to originate mainly from reduced absorption rates of inhomogeneous waves, rather than from enhanced escape probabilities for (quasi-) trapped rays at the Si front surface. The method is further applied to evaluate the effects of a plasmonic nanoparticle array, embedded in a perovskite solar cell stack that is located directly on the microstructured Si surface.

3D RT adaptive path sensing Method: RSSI modelling validation at 4.5 GHz, 28 GHz, and 38 GHz

This paper explains a new Adaptive Path Sensing Method (APSM) for indoor radio wave propagation prediction. Measurement campaigns, which cover indoor line-of-sight (LoS), non-line-of-sight (NLoS) and different room scenarios, are conducted at the new Wireless Communication Centre (WCC) block P15a) of Universiti Teknologi Malaysia (UTM), Johor, Malaysia. The proposed APSM is evaluated through a computerized modelling tool by comparing the Received Signal Strength Indicator (RSSI) with measurement data and the conventional Shooting-Bouncing Ray Tracing (SBRT) method. Simulations of the APSM and SBRT are performed with the same layout of the new WCC block P15a by using the exact building dimensions. The results demonstrate that the proposed method achieves a better agreement with measured data, compared to the conventional SBRT outputs. The reduced computational time and resources required are also important milestones to ray tracing technology. The proposed APSM method can assist engineers and researchers to reduce the time required in modelling and optimizing reliable radio propagation in an indoor environment.

Adaptive 3D ray tracing approach for indoor radio signal prediction at 3.5 GHz

This paper explained an adaptive ray tracing technique in modelling indoor radio wave propagation. As compared with conventional ray tracing approach, the presented ray tracing approach offers an optimized method to trace the travelling radio signal by introducing flexibility and adaptive features in ray launching algorithm in modelling the radio wave for indoor scenarios. The simulation result was compared with measurements data for verification. By analyzing the results, the proposed adaptive technique showed a better improvement in simulation time, power level and coverage in modelling the radio wave propagation for indoor scenario and may benefit in the development of signal propagation simulators for future technologies.

3D deterministic ray tracing method for massive MIMO channel modelling and parameters extraction

Geometric stochastic method and deterministic ray tracing method are two common methods of modelling massive multiple-input multiple-output (MIMO) channels. The former has high computational efficiency but a large number of input parameters need to be extracted from measurements for different environments. Conversely, the latter is more suitable for a specific environment but consumes a lot of computing costs. In this study, a novel three-dimensional (3D) deterministic ray tracing method for massive MIMO channel modelling is proposed. The computational efficiency can be improved in two aspects compared with conventional deterministic ray tracing methods. Firstly, substantial intersection tests used in determining the propagation paths of rays are replaced with the adjacency relationships between tetrahedrons. Secondly, the process of ray tracing is independent of the location of a receiving antenna and therefore repeated ray tracing process is unnecessary for different elements of receiving antenna array. The proposed method is also used as a substitute for measurements to extract input parameters for geometric stochastic channel models. The accuracy of the proposed method in massive MIMO channel modelling and parameters extraction is verified by comparing the results with measurements and other existing channel models.

Representation of discontinuous seismic velocity fields by sigmoidal functions for ray tracing and traveltime modelling

SUMMARYWave-modelling methods based on asymptotic ray theory have a lower computational cost than full wave-equation methods but require a smooth velocity field, though discontinuities may be handled by imposing interface conditions between adjacent blocks. We propose to approximate discontinuous velocity fields with model parametrizations based on smooth, rapidly varying functions known as sigmoidal functions. We have implemented the proposed technique on Cartesian grids using the wavelet theory formalism. Numerical experiments with 2-D and 3-D initial-value and two-point ray tracing in heterogeneous media show that the ray paths and traveltimes produced with the sigmoidal representation are consistent with the results produced by conventional ray tracing in block structures, broadening the scope of classical algorithms based on smooth velocity fields.

Multi-layer imaging method for void defects in ballastless track using forward ray tracing with SAFT

Rapid and precise detection of void disease in ballastless track is fundamental to the repair and maintenance of high-speed rail. Under the difference in material attributes of ballastless track in each layer and the resultant refraction, the calculation of sonic wave travel time can be complex. To this end, ultrasonic imaging is developed for the precise and rapid imaging of void diseases in ballastless track with multi-layer concrete structure. Combining forward ray tracing and synthetic aperture focusing technique (RF-SAFT), the ultrasonic imaging mechanism is developed based on the forward mapping of the refracted ray trajectory to establish the relationship between the refracted ray and multi-layer boundary, so as to identify the void locations. This method is calibrated and validated with finite-element analysis and experiment, which is demonstrated to contribute to efficient high-resolution photography of void diseases in multi-layer concrete ballastless track, with the calculation time reduced by 70% in comparison to the conventional backward ray tracing with SAFT, and higher precision than that by root mean square SAFT. This research can promote responsive and precise detection of void disease in ballastless track to support effective repair and maintenance of high-speed rail.

Outdoor-to-Indoor and Indoor-to-Indoor Propagation Path Loss Modeling Using Smart 3D Ray Tracing Algorithm at 28 GHz mmWave

The goal of the article is to provide a radio propagation algorithm for an outdoor-to-indoor and indoor-to-indoor environment for 5G mmWave in a populated city. This work is done by simulating a smart 3D ray tracing algorithm in MATLAB. The research here is done by taking into account the 28 [GHz] operating frequency which is potential for 5G network. The received results are provided in form of path loss and received signal strength. The results obtained show that a moderate outdoor-to-indoor service can be provided at the above-mentioned frequency. Two indoor path loss models (WINNER II and ITU-R) are also compared here. The literature review provided here is sufficient enough to prove that there is still a huge gap between the conventional ray tracing methods. The proposed model here deals with radio propagations using speedy computations and efficient use of resources. The findings of this paper also include that the path loss is also dependent on the separation between transmitter and receiver, the structure of the building and number and type of the obstructions in the path of RF waves.

DESIGN TOOL TO DEVELOP HIGHLY EFFICIENT OPTOMECHATRONIC SYSTEMS

AbstractIn the domain of optical engineering, optomechatronic systems are predominantly developed using conventional ray tracing methods such as sequential and non-sequential ray tracing. However, the increasing complexity of these systems in combination with the demand for high efficiency and high image quality leads to the fact that conventional methods to develop these systems reach their limits. In order to be able to develop highly efficient systems with high image quality, this contribution introduces a hybrid ray tracing method using an advanced optimization function.

Synthetic image generator for defocusing and astigmatic PIV/PTV

This technical note introduces a synthetic image generator (SIG), referred to as MicroSIG, to be used for particle image/tracking velocimetry (PIV/PTV) analysis involving defocusing or astigmatic particle images. Target applications are experimental setups with volume illumination and small depth of field, in which the defocusing of particles plays a major role. This includes for instance PIV experiments or 3D PTV methods using defocusing or astigmatism to determine the out-of-plane particle position. The software uses an approximated model of spherical lens and conventional ray tracing to create realistic defocused/astigmatic particle images within a reasonable computational time. MicroSIG can be used to compare or optimize different PIV/PTV algorithms using arbitrary flows and different conditions including, non-monodispersed particles, non-uniform illumination, astigmatic optics, non-spherical particles (spheroids). A version of the software, available in Matlab and Python, can be found in the supplementary material and at this link: https://gitlab.com/defocustracking.

Quasioptical modeling of wave beams with and without mode conversion. III. Numerical simulations of mode-converting beams

This work continues a series of papers where we propose an algorithm for quasi-optical modeling of electromagnetic beams with and without mode conversion. The general theory was reported in the first paper of this series, where a parabolic partial differential equation was derived for the field envelope that may contain one or multiple modes with close group velocities. In the second paper, we presented a corresponding code PARADE (PAraxial RAy DEscription) and its test applications to single-mode beams. Here, we report quasi-optical simulations of mode-converting beams for the first time. We also demonstrate that PARADE can model splitting of two-mode beams. The numerical results produced by PARADE show good agreement with those of one-dimensional full-wave simulations and also with conventional ray tracing (to the extent that one-dimensional and ray-tracing simulations are applicable).

Band-limited beam propagator and its application to seismic migration

The ray-tracing technique under the high-frequency assumption has been widely used in seismic wave propagation and migration. However, the practical use of conventional ray tracing is limited in complicated media especially when seismic data are band limited. Besides, the ray-tracing method also suffers from shadow zones in complex media. To alleviate these problems, we have developed a band-limited beam propagator and we apply it in seismic wave propagation and migration, which is flexible to implement and can be friendly to extract angle gathers. To derive the band-limited beam propagator, the band-limited ray-tracing method is adopted to compute the central ray of the beam. These rays in the first Fresnel zone are weighted to obtain the band-limited ray based on the assumption of a local plane wave. Then, the band-limited ray is extended to the band-limited beam propagator using the paraxial approximation. Because the beam propagator has a certain beam width perpendicular to the central ray, it has better illumination than the conventional ray-tracing method, and it could partially alleviate the problem of shadow zones. Finally, we use the band-limited beam propagator to develop a band-limited beam migration and analyze the angle gathers in complicated areas. Numerical examples on synthetic models indicate that the proposed band-limited beam propagator outperforms the conventional ray method in terms of illumination. Its applications in migration determine that it could enhance the imaging quality and produce better angle gathers in a complex area.

Anisotropic 3‐D Ray Tracing and Its Application to Japan Subduction Zone

AbstractA new 3‐D ray tracing technique is developed to determine seismic raypaths and theoretical travel times in weak radial anisotropic media. Anisotropic schemes of the pseudo‐bending technique and Snell's law are derived and used iteratively to find the fastest ray trajectory. Many synthetic tests are performed to evaluate the accuracy of our algorithm and investigate the raypath differences between the 3‐D isotropic and anisotropic rays. The test results show that the travel time and raypath differences are smaller than 0.1 s and 10 km, respectively. Applying our technique to a model of radial anisotropy tomography of the Japan subduction zone, we find visible travel time and raypath differences due to variations of the 3‐D isotropic velocity and radial anisotropy, but the travel time difference caused by the radial anisotropy is generally &lt;~0.1 s and the raypath difference is generally &lt;20 km. Two models of Vp radial anisotropy tomography under Japan are obtained using the isotropic and anisotropic ray tracing codes. The two models are very similar to each other, and they have only small differences (&lt;0.5%) in the amplitudes of isotropic velocity and radial anisotropy. Considering the limited resolution of the current anisotropic tomography models and the effects of damping and smoothing regularizations, the use of the conventional isotropic ray tracing techniques is acceptable at this stage. However, for high‐resolution models of anisotropic tomography in the near future, the 3‐D anisotropic ray tracing will be necessary.

Predictive Model of Difference Between Conventional and Monte Carlo Algorithms for Stereotactic Body Radiation Therapy of Lung Cancer

To compare the conventional Ray Tracing (RT) and Monte Carlo (MC) dose calculations in patients treated with CyberKnife stereotactic ablative radiotherapy and find predictive model of RT/MC calculation difference prior to MC calculation. This is a study on 75 patients treated with stereotactic body radiotherapy of lung cancer. All plans were calculated with conventional RT algorithm and recalculated with MC algorithm using 1% uncertainty. The final MC plan was prescribed to the same coverage and same dose as previous RT plan (D95%). Two inhomogeneity boundaries (encloses the lung tissue - Lung shell, and the target - Target shell) were delineated as a shell structures ± 1 mm in/outside from the lung and ± 1 mm in/outside from the PTV. Lung shell is also proportional to size of lung. Volumes and mean doses of shell structures, numbers of monitor units per fraction (MU/fr), volumes of PTV and GTV, lung mean doses, volumes of lung tissue within the planning target volumes, tumor's localizations and differences in prescribed isodose lines between RT and MC were recorded. Doses and MU/fr were derived from plans calculated with conventional algorithm (RT). Statistical methods were used to find suitable variables (statistically significant) and for multivariable regression model delination. Cross-validation analysis was used to verify the model accuracy. The final prescribed isodose line was on average 80% (range 76-83) and 69% (range 53-78) for RT and MC algorithm respectively what confirmed that dose calculated with conventional algorithm is overestimated. Using the backward selection, a regression model for difference of RT/MC prescribed isodose line was built. Four regression variables (Lung shell, MU/fr, mean doses in Lung shell and Target shell) proved to be significant with p-values < 0,01. The R squared value of the model was 79%. Dividing data in two groups (estimation group consisted of 50 observations, evaluation group consisted of 25 observations) a cross-validation analysis of the model was provided. The cross-validation mean absolute error (CV MAE) equals to 1.8 (±1 in relation to MC 1% calculation uncertainty) and mean error 0.9. No single parameter can predict the difference between conventional (RT) and MC algorithms. The statistical analysis showed four significant variables which can be used in multivariable model to predict the RT/MC difference (RT overestimation). The value of CV MAE showed that our model can highlight the degree of difference from RT results prior to MC calculation. This is our preliminary result and further investigation will follow.

Proposal and analysis of different methodologies for the shading and blocking efficiency in central receivers systems

Nowadays, there are many simulation codes aimed at the simulation of the solar field performance and the optimization of the layout of central receivers systems. These codes should obtain fast and accurately the different efficiency factors of the solar field at different sun positions (representative of the yearly operation). Among these factors, the shading and blocking efficiency is maybe the most demanding one regarding the computational effort.In this paper four non-conventional methodologies are presented for the calculation of the shading and blocking efficiency. The codes have been developed with the ambition of decreasing the computational time without a significant accuracy drop. For that reason, they are suitable for optimization tools. Additionally, a new methodology for the determination of the subset of heliostats with potential for shading or blocking is presented.The performance of the methodologies is evaluated by means of a study of the errors and computational times, which are compared to those reached by a conventional Monte-Carlo ray tracing reference simulation. Results indicate that the proposed methodologies, particularly two of them, present good accuracy and a significant decrease of the computational time. The causes of the main errors of each methodology are also discussed.

Improving Accuracy of Ray-Tracing Prediction in Non Line-of-Sight (NLOS) Urban Street Cell Environment beyond 6GHz

Recently, mobile networks employing high-speed high-capacity communications have been investigated extensively to satisfy the demand for faster and higher-capacity data communications. In one approach, frequencies between 6 and 100GHz are candidates to utilize relatively wide frequency bandwidths. Accordingly, radio propagation loss in these frequency bands must be characterized. Ray-tracing (RT) is the most common modeling approach to predict propagation loss in site-specific scenarios. The accuracy of RT simulations has been investigated in urban street cell environments based on comparison to measurement results and we observed that the difference between RT simulation and measurement results tends to increase as the frequency increases. In this paper, we focus on the shape of building corners at an intersection because it is this shape that is a dominant contributing factor in the region away from the intersection. In order to correct the error in the conventional RT method, we propose an alternative model that considers the detailed shape of the building corner and surface roughness. The performance of the RT simulation using the proposed method is then investigated based on comparison of two different sets of measurement results. Finally, we extract the optimal size and roughness for the proposed modeling method. Consequently, we confirm that using the proposed method with optimized parameters significantly enhances the accuracy compared to the conventional method.

TU-AB-BRC-06: Dose Calculation in Curved Space

Purpose: Microbeam Radiation Therapy is a preclinical method in radiation oncology that modulates radiation fields on a micrometre scale. Dose calculation is challenging due to arising dose gradients and therapeutically important dose ranges. Monte Carlo (MC) simulations, often used as gold standard, are computationally expensive and hence too slow for the optimisation of treatment parameters in future clinical applications. On the other hand, conventional kernel based dose calculation leads to inaccurate results close to material interfaces. The purpose of this work is to overcome these inaccuracies while keeping computation times low. Methods: A point kernel superposition algorithm is modified to account for tissue inhomogeneities. Instead of conventional ray tracing approaches, methods from differential geometry are applied and the space around the primary photon interaction is locally warped. The performance of this approach is compared to MC simulations and a simple convolution algorithm (CA) for two different phantoms and photon spectra. Results: While peak doses of all dose calculation methods agreed within less than 4% deviations, the proposed approach surpassed a simple convolution algorithm in accuracy by a factor of up to 3 in the scatter dose. In a treatment geometry similar to possible future clinical situations differences between Monte Carlo and the differential geometry algorithm were less than 3%. At the same time the calculation time did not exceed 15 minutes. Conclusion: With the developed method it was possible to improve the dose calculation based on the CA method with respect to accuracy especially at sharp tissue boundaries. While the calculation is more extensive than for the CA method and depends on field size, the typical calculation time for a 20×20 mm2 field on a 3.4 GHz and 8 GByte RAM processor remained below 15 minutes. Parallelisation and optimisation of the algorithm could lead to further significant calculation time reductions.

RAY-RAMSES: a code for ray tracing on the fly in N-body simulations

We present a ray tracing code to compute integrated cosmological observables on the fly in AMR N-body simulations. Unlike conventional ray tracing techniques, our code takes full advantage of the time and spatial resolution attained by the N-body simulation by computing the integrals along the line of sight on a cell-by-cell basis through the AMR simulation grid. Moroever, since it runs on the fly in the N-body run, our code can produce maps of the desired observables without storing large (or any) amounts of data for post-processing. We implemented our routines in the RAMSES N-body code and tested the implementation using an example of weak lensing simulation. We analyse basic statistics of lensing convergence maps and find good agreement with semi-analytical methods. The ray tracing methodology presented here can be used in several cosmological analysis such as Sunyaev-Zel'dovich and integrated Sachs-Wolfe effect studies as well as modified gravity. Our code can also be used in cross-checks of the more conventional methods, which can be important in tests of theory systematics in preparation for upcoming large scale structure surveys.