The Longley–Rice model (LR) is a
radio propagation model
Radio propagation is the behavior of radio waves as they travel, or are propagated, from one point to another in vacuum, or into various parts of the atmosphere.
As a form of electromagnetic radiation, like light waves, radio waves are affected ...
: a method for predicting the attenuation of radio signals for a
telecommunication
Telecommunication is the transmission of information by various types of technologies over wire, radio, optical, or other electromagnetic systems. It has its origin in the desire of humans for communication over a distance greater than tha ...
link in the
frequency range
A frequency band is an interval in the frequency domain, delimited by a lower frequency and an upper frequency. The term may refer to a radio band or an interval of some other spectrum.
The frequency range of a system is the range over which ...
of 40
MHz to 100
GHz.
[John S. Seybold ''Introduction to RF propagation'' John Wiley and Sons, 2005 , page 143]
Longley-Rice is also known as the irregular terrain model (ITM). It was created by scientists Anita Longley and Phil Rice of the then Central Radio Propagation Laboratory in Boulder, Colorado for the needs of frequency planning in
television broadcasting
A television network or television broadcaster is a telecommunications network for distribution of television program content, where a central operation provides programming to many television stations or pay television providers. Until the mid- ...
in the
United States
The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., federal district, five ma ...
in the 1960s and was extensively used for preparing the tables of channel allocations for
VHF
Very high frequency (VHF) is the ITU designation for the range of radio frequency electromagnetic waves (radio waves) from 30 to 300 megahertz (MHz), with corresponding wavelengths of ten meters to one meter.
Frequencies immediately below VHF ...
/
UHF
Ultra high frequency (UHF) is the ITU designation for radio frequencies in the range between 300 megahertz (MHz) and 3 gigahertz (GHz), also known as the decimetre band as the wavelengths range from one meter to one tenth of a meter (on ...
broadcasting there. LR has two parts: a model for predictions over an area and a model for
point-to-point link
In telecommunications, a point-to-point connection refers to a communications connection between two communication endpoints or nodes. An example is a telephone call, in which one telephone is connected with one other, and what is said by one ca ...
predictions.
Publications
A description of the method was published by the U.S. government under the title ''"Prediction of tropospheric radio transmission loss over irregular terrain. A computer method-1968"'',
A. G. Longley and
P. L. Rice, ESSA Tech. Rep. ERL 79-ITS 67, U.S. Government Printing Office, Washington, DC, July 1968. This document followed on an earlier publication titled ''"Transmission loss predictions for tropospheric communication circuits"'', P.L. Rice, Volume I & II, National Bureau of Standards, Tech. Note 101.
The Longley–Rice model was proposed for frequencies between 20 MHz and 20 GHz for different scenarios and different heights of transmitting and receiving antennas. The model presents a generalization of the received signal power without a detailed characterization of the channel. This model uses statistical resources to compensate for the characterization of the channel, which depends on the variables of each scenario and environment.
The variation of the signal is determined by the prediction model according to the atmospheric changes, topographic profile and free space. These variations are described with the help of statistical estimates which have deviations that contribute to the total attenuation of the signal. The statistical estimates or attenuation variables of this prediction model are: I) Situation variability (Ys); II) Time variability (Yt); II) Location variability (YL). The reference attenuation (W) is determined as a function of the distance, attenuation variables and an urban factor for an area or point-to-point.
Because of this variability, there could be deviations (δ) more or less significant to the attenuation of the transmitted signal. The received signal (W) is obtained signal level attenuated in free space (W0) attenuated by the sum of the attenuation formed by random variables. If transmitter and receiver are at known points, the location variable has a value of zero.
The reference attenuation defined as a function of distance also features 3 ranges for prediction: I) line-of-sight; II) diffraction; III) scatter. For each of these ranges, there are attenuation coefficients defined according to link geometry. These variables also consider the topography that is defined as terrain irregularity parameter ∆h(d) for a reference distance (D0).
Software
Several applications use the Longley-Rice Model. Examples are
Nautel (requires free registration)*
SPLAT!Radio MobileQRadioPredictPathloss 5ProbeTowerCoverage.com
Source code and development libraries
Original ITS sources (FORTRAN and C++)C++C#NuGet Packageitmlogic Python package
ref name=Oughton20>Oughton et al., (2020). itmlogic: The Irregular Terrain Model by Longley and Rice. Journal of Open Source Software, 5(51), 2266, https://doi.org/10.21105/joss.02266
Port of the Original ITS sources to Free Pascal/DelphiITM Museum (versions 1, 1.2.1, 1.2.2 and background)
References
External links
* https://www.researchgate.net/publication/250615289_Comparison_of_Longley-Rice_ITM_and_ITWOM_propagation_models_for_DTV_and_FM_broadcasting
* https://www.researchgate.net/publication/264003637_Comparison_of_Longley-Rice_ITU-R_P1546_and_Hata-Davidson_propagation_models_for_DVB-T_coverage_prediction
{{DEFAULTSORT:Longley-Rice model
Radio frequency propagation model