Choose a Propagation Model
Propagation models allow you to predict the propagation and attenuation of radio
signals as the signals travel through the environment. You can simulate different models
by using the propagationModel
function. Additionally, you can determine the range and
path loss of radio signals in these simulated models by using the range
and pathloss
functions.
The following sections describe various propagation and ray tracing models. The tables
in each section list the models that are supported by the
propagationModel
function and compare, for each model, the
supported frequency ranges, model combinations, and limitations.
Atmospheric
Atmospheric propagation models predict path loss between sites as a function of distance. These models assume lineofsight (LOS) conditions and disregard the curvature of the Earth, terrain, and other obstacles.
Model  Description  Frequency  Combinations  Limitations 

freespace (FreeSpace )  Ideal propagation model with clear line of sight between transmitter and receiver  No enforced range  Can be combined with rain, fog, and gas  Assumes line of sight 
rain (Rain )  Propagation of a radio wave signal and its path loss in rain. For more information, see [3].  1 GHz to 1000 GHz  Can be combined with any other propagation model  Assumes line of sight 
gas (Gas )  Propagation of radio wave signal and its path loss due to oxygen and water vapor. For more information, see [5].  1GHz to 1000 GHz  Can be combined with any other propagation model  Assumes line of sight 
fog (Fog )  Propagation of the radio wave signal and its path loss in cloud and fog. For more information, see [2].  10GHz to 1000 GHz  Can be combined with any other propagation model  Assumes line of sight 
Empirical
Like atmospheric propagation models, empirical models predict path loss as a function of distance. Unlike atmospheric models, the closein empirical model supports nonlineofsight (NLOS) conditions.
Terrain
Terrain propagation models assume that propagation occurs between two points over a slice of terrain. Use these models to calculate the pointtopoint path loss between sites over irregular terrain, including buildings.
Terrain models calculate path loss from freespace loss, terrain and obstacle diffraction, ground reflection, atmospheric refraction, and tropospheric scatter. They provide path loss estimates by combining physics with empirical data.
Model  Description  Frequency  Combinations  Limitations 

longleyrice (LongleyRice )  Also known as Irregular Terrain Model (ITM). For more information, see [4].  20 MHz to 20 GHz  Can be combined with rain, fog, and gas  Antenna height minimum is 0.5 m and maximum is 3000 m 
tirem (TIREM )  Terrain Integrated Rough Earth Model™  1 MHz to 1000 GHz  Can be combined with rain, fog, and gas 

Ray Tracing
Ray tracing models, represented by RayTracing
objects, compute propagation paths
using 3D environment geometry [7][8]. They 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 freespace 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 [5][6] at the specified
frequency.
While the other supported models compute single propagation paths, ray tracing models compute multiple propagation paths.
These models support both 3D outdoor and indoor environments.
Ray Tracing Method  Description  Frequency  Combinations  Limitations 

shooting and bouncing rays (SBR) 
 100 MHz to 100 GHz  Can be combined with rain, fog, and gas  Does not include effects from diffraction, refraction, and scattering 
image 
 100 MHz to 100 GHz  Can be combined with rain, fog, and gas  Does not include effects from diffraction, refraction, and scattering 
SBR 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 [9][10]. 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 [10]. 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 3D 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 singleprecision floatingpoint computations.
Image Method
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 singleprecision floatingpoint computations.
References
[1] Sun, Shu, Theodore S. Rappaport, Timothy A. Thomas, Amitava Ghosh, Huan C. Nguyen, Istvan Z. Kovacs, Ignacio Rodriguez, Ozge Koymen, and Andrzej Partyka. “Investigation of Prediction Accuracy, Sensitivity, and Parameter Stability of LargeScale Propagation Path Loss Models for 5G Wireless Communications.” IEEE Transactions on Vehicular Technology 65, no. 5 (May 2016): 2843–60. https://doi.org/10.1109/TVT.2016.2543139.
[2] International Telecommunications Union Radiocommunication Sector. Attenuation due to clouds and fog. Recommendation P.8406. ITUR, approved September 30, 2013. https://www.itu.int/rec/RRECP.8406201309S/en.
[3] International Telecommunications Union Radiocommunication Sector. Specific attenuation model for rain for use in prediction methods. Recommendation P.8383. ITUR, approved March 8, 2005. https://www.itu.int/rec/RRECP.8383200503I/en.
[4] Hufford, George A., Anita G. Longley, and William A.Kissick. A Guide to the Use of the ITS Irregular Terrain Model in the Area Prediction Mode. NTIA Report 82100. National Telecommunications and Information Administration, April 1, 1982.
[5] International Telecommunications Union Radiocommunication Sector. Effects of building materials and structures on radiowave propagation above about 100MHz. Recommendation P.20401. ITUR, approved July 29, 2015. https://www.itu.int/rec/RRECP.20401201507I/en.
[6] International Telecommunications Union Radiocommunication Sector. Electrical characteristics of the surface of the Earth. Recommendation P.5275. ITUR, approved August 14, 2019. https://www.itu.int/rec/RRECP.5275201908I/en.
[7] 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.
[8] 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.
[9] International Telecommunications Union Radiocommunication Sector. Propagation by diffraction. Recommendation P.52615. ITUR, approved October 21, 2019. https://www.itu.int/rec/RRECP.52615201910I/en.
[10] 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.