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Choose a Propagation Model

Introduction

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 line-of-sight (LOS) conditions and disregard the curvature of the Earth, terrain, and other obstacles.

ModelDescriptionFrequencyCombinationsLimitations
freespaceIdeal propagation model with clear line of sight between transmitter and receiverNo enforced rangeCan be combined with rain, fog, and gasAssumes line of sight
rainPropagation of a radio wave signal and its path loss in rain. For more information, see [3]. 1 to 1000 GHzCan be combined with any other propagation modelAssumes line of sight
gasPropagation of radio wave signal and its path loss due to oxygen and water vapor. For more information, see [5].1 to 1000 GHzCan be combined with any other propagation modelAssumes line of sight
fogPropagation of the radio wave signal and its path loss in cloud and fog. For more information, see [2].10 to 1000 GHzCan be combined with any other propagation modelAssumes line of sight

Empirical

Like atmospheric propagation models, empirical models predict path loss as a function of distance. Unlike atmospheric models, the close-in empirical model supports non-line-of-sight (NLOS) conditions.

ModelDescriptionFrequencyCombinationsLimitations
close-inPropagation of signals in urban macro cell scenarios. For more information, see [1].No enforced rangeCan be combined with rain, fog, and gas

Terrain

Terrain propagation models assume that propagation occurs between two points over a slice of terrain. Use these models to calculate the point-to-point path loss between sites over irregular terrain, including buildings.

Terrain models calculate path loss from free-space loss, terrain and obstacle diffraction, ground reflection, atmospheric refraction, and tropospheric scatter. They provide path loss estimates by combining physics with empirical data.

ModelDescriptionFrequencyCombinationsLimitations
longley-riceAlso known as Irregular Terrain Model (ITM). For more information, see [4].20 MHz to 20 GHzCan be combined with rain, fog, and gasAntenna height minimum is 0.5 m and maximum is 3000 m
tiremTerrain Integrated Rough Earth Model™1 MHz to 1000 GHzCan be combined with rain, fog, and gas
  • Requires access to external TIREM library

  • Antenna height maximum is 30000 m

Ray Tracing

Ray tracing models compute propagation paths using 3-D environment geometry ([8],[9]). 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 both 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 ([6],[7]) at the specified frequency.

While the other supported models compute single propagation paths, ray tracing models compute multiple propagation paths.

These models support both 3-D outdoor and indoor environments.

Ray Tracing MethodDescriptionFrequencyCombinationsLimitations
image
  • Supports up to two path reflections and calculates exact propagation paths.

  • Computational complexity increases exponentially with the number of reflections

100 MHz to 100 GHzCan be combined with rain, fog, and gasDoes not include effects from refraction, diffraction, and scattering
shooting and bouncing rays (SBR)
  • Supports up to 10 path reflections and calculates approximate propagation paths. As a result, the locations of receiver sites calculated by the SBR method are not exact. The accuracy of calculated propagation paths decreases as the length of the paths increases.

  • Computational complexity increases linearly with the number of reflections. As a result, the SBR method is generally faster than the image method.

100 MHz to 100 GHzCan be combined with rain, fog, and gasDoes not include effects from refraction, diffraction, and scattering

Algorithms

This illustration shows how the image method calculates the propagation path of a single reflection ray from a transmitter, Tx, to a receiver, Rx. The image method locates the image of Tx, Tx', with respect to a planar reflection surface. Then, the method connects Tx' and Rx with a line segment. If the line segment intersects the planar reflection surface, shown as Q in the illustration, then a valid path from Tx to Rx exists. The method determines paths with multiple reflections by recursively extending these steps.

Ray tracing using the image method

This illustration shows how the SBR method calculates the propagation path of the same ray. The SBR method launches many rays from a geodesic sphere centered at Tx. Then, the method traces every ray from Tx as it reflects, diffracts, refracts, or scatters off surrounding objects. Note that the implementation considers only reflections. For each launched ray, the method surrounds Rx with a sphere, called a reception sphere, with a radius that is proportional to the angular separation of the launched rays and the distance the ray travels. If the ray intersects the sphere, then the model considers the ray a valid path from Tx to Rx.

Ray tracing using the SBR method

References

[1] Sun, S.,Rapport, T.S., Thomas, T., Ghosh, A., Nguyen, H., Kovacs, I., Rodriguez, I., Koymen, O.,and Prartyka, A. "Investigation of prediction accuracy, sensitivity, and parameter stability of large-scale propagation path loss models for 5G wireless communications." IEEE Transactions on Vehicular Technology, Vol.65, No 5, pp 2843-2860, May 2016.

[2] ITU-R P.840-6. "Attenuation due to cloud and fog." Radiocommunication Sector of ITU

[3] ITU-R P.838-3. "Specific attenuation model for rain for use in prediction methods." Radiocommunication Sector of ITU

[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 82-100. Pg-7.

[5] ITU-R P.676-11. "Attenuation by atmospheric gases." Radiocommunication Sector of ITU

[6] ITU-R P.2040-1. "Effects of Building Materials and Structures on Radiowave Propagation Above 100MHz." International Telecommunications Union - Radiocommunications Sector (ITU-R). July 2015.

[7] ITU-R P.527-5. "Electrical characteristics of the surface of the Earth." International Telecommunications Union - Radiocommunications Sector (ITU-R). August 2019.

[8] 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.

[9] 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.

See Also

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