LongleyRice

Longley-Rice propagation model

Description

Model the behavior of electromagnetic radiation from a point of transmission over irregular terrain, including buildings, by using the Longley-Rice model, also known at the Irregular Terrain Model (ITM). For more information about the model, see [1]. Represent the model by using a LongleyRice object.

The Longley-Rice model:

• Is designed for frequencies from 20 MHz to 20 GHz, distances from 1 to 2000 km, and antenna heights from 0.5 to 3000 m.

• Calculates path loss from free-space loss, terrain and obstacle diffraction, ground reflection, atmospheric refraction, and tropospheric scatter.

• Provides path loss estimates by combining physics with empirical data statistics.

To predict path loss in scenes that feature buildings, such as urban environments, consider using a ray tracing propagation model. For more information about ray tracing models, see RayTracing.

Note

The LongleyRice object implements the point-to-point mode of the model, which uses terrain data to predict the loss between two points.

Creation

Create a LongleyRice object by using the propagationModel function.

Properties

AntennaPolarization — Polarization of transmitter and receiver antennas

"horizontal" (default) | "vertical"

Polarization of transmitter and receiver antennas, specified as "horizontal" or "vertical". This object assumes both antennas have the same polarization.

Data Types: char | string

GroundConductivity — Conductivity of ground, in S/m

0.005 (default) | scalar

Conductivity of the ground, in S/m, specified as a scalar. The model uses this value to calculate path loss due to ground reflection and diffraction. The default value corresponds to average ground.

Data Types: double

GroundPermittivity — Real relative permittivity of ground

15 (default) | scalar

Real relative permittivity of the ground, specified as a scalar. Real relative permittivity is expressed as the real part of the ratio of complex absolute material permittivity to the absolute permittivity of vacuum. The model uses this value to calculate the path loss due to ground reflection and diffraction. The default value corresponds to average ground.

Data Types: double

AtmosphericRefractivity — Atmospheric refractivity near ground, in N-units

301 (default) | scalar

Atmospheric refractivity near the ground, in N-Units, specified as a scalar. The model uses this value to calculate the path loss due to refraction through the atmosphere and tropospheric scatter. The default value corresponds to average atmospheric conditions.

Data Types: double

ClimateZone — Radio climate zone

"continental-temperate" (default) | "equatorial" | "continental-subtropical" | "maritime-subtropical" | "desert" | "maritime-over-land" | "maritime-over-sea"

Radio climate zone, specified as one of these options:

• "continental-temperate"

• "equatorial"

• "continental-subtropical"

• "maritime-subtropical"

• "desert"

• "maritime-over-land"

• "maritime-over-sea"

The model uses this value to calculate the variability due to changing atmospheric conditions. The default value corresponds to average atmospheric conditions in a particular climate zone.

Data Types: char | string

TimeVariabilityTolerance — Time variability tolerance level

0.5 (default) | scalar in the range [0.001, 0.999]

Time variability tolerance level of the path loss, specified as a scalar in the range [0.001, 0.999]. Time variability represents long-term variability (including atmospheric conditions) but neglects short-term variability such as fast multipath fading. This value gives the required system reliability expressed as the fraction of time during which the actual path loss is expected to be less than or equal to the model prediction.

Data Types: double

SituationVariabilityTolerance — Situation variability tolerance level

0.5 (default) | scalar in the range [0.001, 0.999]

Situation variability tolerance level of the path loss, specified as a scalar in the range [0.001, 0.999]. Situation variability occurs due to uncontrolled or hidden random variables. This value gives the required system confidence expressed as the fraction of similar situations for which the actual path loss is expected to be less than or equal to the model prediction.

Data Types: double

Object Functions

pathloss	Path loss of radio wave propagation
add	Add propagation models

Examples

Model Coverage Using Longley-Rice Model

Display the coverage area for a transmitter using the Longley-Rice model.

pm = propagationModel("longley-rice");
tx = txsite("Name","Apple Hill","Latitude",42.3001,"Longitude",-71.3604);
coverage(tx,pm,"SignalStrengths",-100:-5)

Increase the time and situation variability tolerance levels from 0.5 (the default) to 0.9. Display the coverage area for the transmitter using the updated propagation model.

pm.TimeVariabilityTolerance = 0.9;
pm.SituationVariabilityTolerance = 0.9;
coverage(tx,pm,"SignalStrengths",-100:5)

The coverage area is smaller for the model with higher variability tolerance levels.

More About

N-Units

The refractive index of air, n, is related to the dielectric constants of the gas constituents of an air mixture. The numerical value of n is only slightly larger than 1. To make the calculation more convenient, you can use N units, which are given by the formula: $$N=(n-1)\times {10}^6$$.

References

[1] 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. National Telecommunications and Information Administration, April 1, 1982.

[2] Seybold, John S. Introduction to RF Propagation. Hoboken, N.J: Wiley, 2005.

Version History

Introduced in R2019b