Ray-based Simulations Research Articles

Virtual assessment of phone booths' acoustic performance in laboratory and office environments

The irrelevant speech noise is one of the significant issues affecting workers' productivity and comfort. Acoustic furniture is the most common solution addressing this problem: mobile phone booths and partially closed workstations are two examples. The acoustic performance of such devices is defined with laboratory tests according to ISO 23351-1:2020. The sound power level measured in reverberation rooms with and without the product determines the reduction of speech A-weighted sound power level (DS,A). However, predicting acoustic performance in real-world scenarios is still challenging. The present work explores the discrepancies between DS,A, and apparent speech reduction (D'S,A) through numerical models. The study assesses the performance difference between a calibrated virtual reverberation room and virtual open-plan offices maintaining the same acoustic properties, i.e., sound transmission and sound absorption, of a typical two-person phone booth. Moreover, the study investigates the fluctuation on D'S,A changing main room acoustic criteria, e.g., the reverberation time (T) and the total absorption area (A). Results help define ray-based simulations' reliability in predicting furniture ensembles' acoustic performance.

Analytic Rendering and Hardware-Accelerated Simulation for Scientific Applications

Advances in entertainment-targeted rendering technology have been leveraged for scientific analysis. Recent progress in both hardware and software capabilities have spurred development in analytic rendering: rendering capabilities optimized for analysis, particularly 3-D spatial analysis. These efforts also leverage hardware-accelerated ray tracing for high-fidelity rendering, which unlocks the potential to use such acceleration methods directly in ray-based simulations such as radiative transfer. This special issue presents the new ANARI API standard for analytic rendering and examples of analytic rendering and hardware-accelerated simulation where such APIs could be used.

Ray-Based Modeling of Directional Millimeter-Wave V2V Transmissions in Highway Scenarios

Due to the need for larger bandwidth, future mobile networks may primarily operate over millimeter-wave (mmWave) bands. In this regard, one of the central research topics today is mmWave channel modeling. However, highly mobile vehicle-to-vehicle (V2V) mmWave channels pose an open question because conducting measurements may be challenging in this environment. The existing publications on mmWave V2V channel modeling consider line-of-sight (LoS) or single-blocker scenarios. Accordingly, the impact of interference from adjacent vehicles is not taken into account. Conventional analytical models suggest that path loss (PL) strikes equally in all directions whereas measurements are inherently directional, especially in the case of mmWave propagation. Recently, it was proposed to synthesize the omnidirectional PL from directional measurements. However, with this method, the resulting PL is underestimated. Moreover, theoretical models assume that vehicular transceivers follow a certain predetermined distribution, which may not be accurate in real-world scenarios. Several works take into account the directionality of an antenna pattern when the antenna orientation is known. However, the effects of reflection, diffraction, and transmission through obstacles are not considered. One way to avoid these limitations is to use ray-based simulations. However, the ray-launching (RL) approach does not specify any criteria for the directionality of the antenna patterns. Assuming omnidirectional PL appears impractical for mmWave transmission where directional communication is crucial to combat high PL. In this paper, we propose an approach for synthesizing directional PL based on extensive RL modeling. For the obtained directional and omnidirectional PL, we parametrize the close-in (CI) and float-intercept (FI) channel models. As a result of our modeling, from 0.1 to 2.7 for the LoS and from 0.1 to 2.6 for the non-LoS (NLoS) higher PL exponent is observed as compared to the omnidirectional case.

Integration and Application of Microlens Arrays Within Heads-Up Displays

The proposed work targets a fundamental challenge in heads-up display technology—in that such displays must bring about tight imaging with a flat form factor to support integration within eyewear. A Gabor superlens, being coupled plano-concave and plano-convex microlens arrays (MLAs), is developed to meet this challenge. The MLAs are designed and optimized, via tradespace analyses and ray-based simulations, and then formed with a specialized fabrication process. The process applies plasma pretreatment to the substrate followed by dispensing, curing, and casting of microlenses on the substrate to realize arrays with the necessary diameters and radii of curvature. The plano-concave and plano-convex MLAs are coupled to form the superlens, which is packaged with a baffle and microdisplay to function as the heads-up display. Ray-based simulations and experimental characterizations are carried out on the modulation transfer function of the display to define its resolution. It is found that the superlens can bring about strong imaging performance—with a resolution of up to 30 cycles/mm—as well as the tight imaging and flat form factor that are needed for emerging heads-up display technologies.

Model for Ray-Based UTD Simulations of the Human Body Shadowing Effect in 5G Wireless Systems

Shadowing effects caused by the obstructing presence of a human body can result in increased path loss in indoor wireless systems. This paper proposes a simplified model of a human body for use in ray-tracing simulations of indoor wireless communication systems based on the uniform theory of diffraction (UTD). The human body shadowing effect was first investigated using measurements and computer simulations employing the finite-difference time-domain method (FDTD). Based on the results, a human body model was elaborated for use in ray-based Remcom XGtd software. The model was developed for the 3.6 GHz band, which has been allocated for 5G wireless systems in many countries.

Characterization of Radio Links at 60 GHz Using Simple Geometrical and Highly Accurate 3-D Models

In order to effectively deploy high data rate millimeter-wave communication systems in urban environments, accurate information about the radio-wave propagation channel is essential. Radio-wave propagation in urban scenarios strongly depends on the topography of the immediate surroundings. A measurement campaign has been carried out to evaluate the impact of propagation effects on the radio channel at the rooftop level of buildings. In the simulation part of the paper, we present two 3-D models produced with different techniques: first, a simple geometrical model and, second, a highly accurate close-range photogrammetry model; the latter replicates the detailed building geometry. To construct a highly accurate 3-D model, images obtained by an unmanned aerial vehicle were utilized together with the photogrammetry technique. In this paper, we provide a thorough comparison between the measured and the simulated power delay profiles by conducting shooting-and-bouncing ray-based simulations for the rooftop scenario using two 3-D models of different accuracy. The results show that the use of the close-range photogrammetry model can provide better propagation prediction at millimeter-wave frequencies.

Toward Massive Ray-Based Simulations of mmWave Small Cells on Open Urban Maps

High-rate access in outdoor urban areas using extremely high frequency (EHF) bands, known as millimeter-wave (mmWave) spectrum, requires a dense deployment of wireless small cells in order to provide continuous coverage to serve bandwidth-hungry users. At the same time, to be able to collect a sufficient amount of data for constructing detailed EHF propagation models, a considerable number of various landscape maps across different scenarios have to be considered. This letter develops a shoot-and-bounce ray (SBR) -based methodology capable of characterizing the mmWave propagation in urban outdoor conditions. In particular, our methodology aims to capture a large number of small cells within accurate, real city maps and then to utilize an algorithm of automatic transmitter placement. Hence, our contribution is to provide a suitable tool that is able to handle massive ray-based simulations within a reasonable time frame. In particular, we demonstrate and verify that a shift from simulating three-dimensional (3-D) to evaluating 2-D environments significantly reduces computation time while only slightly decreasing the simulation accuracy.

Acoustic noise interferometry in the Straits of Florida at 100 m depth: A ray-based interpretation

Cross-correlation function of ambient and shipping noise recorded simultaneously by two hydrophones provides an estimate of the acoustic Green's function, which describes deterministic sound propagation between the hydrophones and can be used to estimate physical parameters of the water column and seafloor. This paper presents results of an experimental investigation of acoustic noise interferometry in 100 m-deep water in the Straits of Florida. Acoustic noise was recorded continuously for about six days at three points near the seafloor. Coherent acoustic arrivals are successfully identified in the 20–70 Hz frequency band for pairs of hydrophones separated by ranges of 5.0 and 9.8 km. The measured noise cross-correlation functions are compared to ray-based simulations of Green's functions, with generally good agreement between correlation functions and simulations. Ray-based simulations are shown to reproduce multipath features of the measured correlation functions, which are due to multiple surface and bottom reflections. The feasibility of passive acoustic remote sensing using a few hydrophones in a shallow-water waveguide will be discussed. [Work supported by NSF, ONR, and NAVAIR.]