RayTracing
Ray tracing propagation model
Description
Ray tracing models compute propagation paths using 3-D environment geometry [1][2] . Represent a ray tracing model by
using a RayTracing object.
Ray tracing models:
Are valid from 100 MHz to 100 GHz.
Compute multiple propagation paths. Other propagation models compute only single propagation paths.
Support 3-D outdoor and indoor environments.
Determine the path loss and phase shift of each ray using electromagnetic analysis, including tracing the horizontal and vertical polarizations of a signal through the propagation path. The path loss includes free-space loss and reflection losses. For each reflection, the model calculates losses on the horizontal and vertical polarizations by using the Fresnel equation, the incident angle, and the relative permittivity and conductivity of the surface material [3][4] at the specified frequency.
You can create ray tracing models that use either the shooting and bouncing rays (SBR) method or the image method.
Creation
Create a RayTracing object by using the propagationModel
function.
Properties
Examples
Model Propagation Paths Using SBR and Image Methods
Show reflected propagation paths in Chicago by using the SBR and image methods.
Create a Site Viewer with buildings in Chicago. For more information about the osm file, see [1].
viewer = siteviewer("Buildings","chicago.osm");
Create a transmitter site on a building and a receiver site near another building.
tx = txsite("Latitude",41.8800, ... "Longitude",-87.6295, ... "TransmitterFrequency",2.5e9); show(tx) rx = rxsite("Latitude",41.8813452, ... "Longitude",-87.629771, ... "AntennaHeight",30); show(rx)
Create a ray tracing model. Use the image method and calculate paths with up to one reflection. Then, display the propagation paths.
pm = propagationModel("raytracing","Method","image", ... "MaxNumReflections",1); raytrace(tx,rx,pm)
For this ray tracing model, there is one propagation path from the transmitter to the receiver.
Update the ray tracing model to use the SBR method and to calculate paths with up to two reflections. Display the propagation paths.
pm.Method = "sbr";
pm.MaxNumReflections = 2;
clearMap(viewer)
raytrace(tx,rx,pm)
The updated ray tracing model shows three propagation paths from the transmitter to the receiver.
Appendix
[1] The osm file is downloaded from https://www.openstreetmap.org, which provides access to crowd-sourced map data all over the world. The data is licensed under the Open Data Commons Open Database License (ODbL), https://opendatacommons.org/licenses/odbl/.
Model Coverage Using Ray Tracing
Create a Site Viewer with buildings in Chicago. For more information about the .osm file, see [1].
viewer = siteviewer("Buildings","chicago.osm");
Create a transmitter site on a building and a receiver site near another building.
tx = txsite("Latitude",41.8800, ... "Longitude",-87.6295, ... "TransmitterFrequency",2.5e9); show(tx)
Create a ray tracing model. By default, ray tracing models use the SBR method. Set the maximum number of reflections to 2. Then, display the coverage map.
pm = propagationModel("raytracing","Method","sbr", ... "MaxNumReflections",2); coverage(tx,pm,"SignalStrengths",-100:5)
Appendix
[1] The .osm file is downloaded from https://www.openstreetmap.org, which provides access to crowd-sourced map data all over the world. The data is licensed under the Open Data Commons Open Database License (ODbL), https://opendatacommons.org/licenses/odbl/.
More About
Shooting and Bouncing Rays Method
The shooting and bouncing rays (SBR) method finds an approximate number of propagation paths with exact geometric accuracy. You can use this method to find paths with up to 10 path reflections.
The computational complexity of the SBR method increases linearly with the number of reflections. As a result, the SBR method is generally faster than the image method.
This figure illustrates the SBR method for calculating propagation paths from a transmitter, Tx, to a receiver, Rx.
The SBR method launches many rays from a geodesic sphere centered at Tx. The geodesic sphere enables the model to launch rays that are approximately uniformly spaced.
Then, the method traces every ray from Tx and can model different types of interactions between the rays and surrounding objects, such as reflections, diffractions, refractions, and scattering. Note that the current implementation of the SBR method considers only reflections.
When a ray hits a flat surface, shown as R, the ray reflects based on the law of reflection.
When a ray hits an edge, shown as D, the ray spawns many diffracted rays based on the law of diffraction [5][6]. Each diffracted ray has the same angle with the diffracting edge as the incident ray. The diffraction point then becomes a new launching point and the SBR method traces the diffracted rays in the same way as the rays launched from Tx. A continuum of diffracted rays forms a cone around the diffracting edge, which is commonly known as a Keller cone [6]. The current implementation of the SBR method does not consider edge diffractions.
For each launched ray, the SBR method surrounds Rx with a sphere, called a reception sphere, with a radius that is proportional to the distance the ray travels and the average number of degrees between the launched rays. If the ray intersects the sphere, then the model considers the ray a valid path from Tx to Rx. The SBR method corrects the valid paths so that the paths have exact geometric accuracy.
When you increase the number of rays by decreasing the number of degrees between rays, the reception sphere becomes smaller. As a result, in some cases, launching more rays results in fewer or different paths. This situation is more likely to occur with custom 3-D scenarios created from STL files or triangulation objects than with scenarios that are automatically generated from OpenStreetMap® buildings and terrain data.
The SBR method finds paths using single-precision floating-point computations.
Image Method
The image method finds an exact number of propagation paths with exact geometric accuracy. You can use this method to find paths with up to 2 path reflections. The computational complexity of the image method increases exponentially with the number of reflections.
This figure illustrates the image method for calculating the propagation path of a single reflection ray for the same transmitter and receiver as the SBR method. The image method locates the image of Tx with respect to a planar reflection surface, Tx'. Then, the method connects Tx' and Rx with a line segment. If the line segment intersects the planar reflection surface, shown as R in the figure, then a valid path from Tx to Rx exists. The method determines paths with multiple reflections by recursively extending these steps. The image method finds paths using single-precision floating-point computations.
References
[1] Yun, Zhengqing, and Magdy F. Iskander. “Ray Tracing for Radio Propagation Modeling: Principles and Applications.” IEEE Access 3 (2015): 1089–1100. https://doi.org/10.1109/ACCESS.2015.2453991.
[2] Schaubach, K.R., N.J. Davis, and T.S. Rappaport. “A Ray Tracing Method for Predicting Path Loss and Delay Spread in Microcellular Environments.” In [1992 Proceedings] Vehicular Technology Society 42nd VTS Conference - Frontiers of Technology, 932–35. Denver, CO, USA: IEEE, 1992. https://doi.org/10.1109/VETEC.1992.245274.
[3] International Telecommunications Union Radiocommunication Sector. Effects of building materials and structures on radiowave propagation above about 100MHz. Recommendation P.2040-1. ITU-R, approved July 29, 2015. https://www.itu.int/rec/R-REC-P.2040-1-201507-I/en.
[4] International Telecommunications Union Radiocommunication Sector. Electrical characteristics of the surface of the Earth. Recommendation P.527-5. ITU-R, approved August 14, 2019. https://www.itu.int/rec/R-REC-P.527-5-201908-I/en.
[5] International Telecommunications Union Radiocommunication Sector. Propagation by diffraction. Recommendation P.526-15. ITU-R, approved October 21, 2019. https://www.itu.int/rec/R-REC-P.526-15-201910-I/en.
[6] Keller, Joseph B. “Geometrical Theory of Diffraction.” Journal of the Optical Society of America 52, no. 2 (February 1, 1962): 116. https://doi.org/10.1364/JOSA.52.000116.
Version History
Introduced in R2019bSee Also
Functions
propagationModel|raytrace|coverage|sigstrength|buildingMaterialPermittivity|earthSurfacePermittivity
Objects
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