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Comparison of Longley-Rice, ITM and ITWOM
propagation models for DTV and FM Broadcasting
Stylianos Kasampalis, Pavlos I. Lazaridis, Zaharias D. Zaharis, Aristotelis Bizopoulos, Spiridon
Zettas and John Cosmas, Senior Member IEEE.
Abstract— With the rapid deployment of digital TV,
there is an increasing need for accurate point-to-area
prediction tools. There is a great deal of propagation
models for coverage prediction of DTV. Some of them are
pure empirical models, and others are mixed, empirical-
analytical models, based on measurement campaigns and
electromagnetic theory. The aim of this paper is to
compare accurate measurements taken by a Rohde &
Schwarz FSH-3 portable spectrum analyzer and precision
antennas (biconical and log-periodic), with simulation
results derived from coverage prediction models, like the
NTIA-ITS Longley-Rice model, the ITM (Irregular
Terrain Model) using the 3-arc-second SRTM (Satellite
Radar Topography Mission) data that is available freely,
and the newer ITWOM (Irregular Terrain with
Obstructions Model) model which combines equations
from ITU-R P.1546 model with Beer's law and Snell's law.
Furthermore, measurements for analog FM broadcasting
are compared to predictions from the above mentioned
models.
Keywords—DVB-T, NTIA-ITS, Longley-Rice, ITM,
ITWOM, SRTM, ITU-R P.1546, FM.
I. INTRODUCTION
In order to take full advantage of DTV services and
characteristics and to obtain a satisfactory coverage,
measurement campaigns are required, as well as field trials,
comparing simulation and laboratory results with
measurements. The scope of this research, is to provide
coverage prediction maps for DTV and FM radio services, in
the region of Thessaloniki – Greece, and to validate
simulation results with field measurements. It is well known
that the coverage of a transmitter can only be obtained by
extensive measurement campaigns. However, on-site
measurements are inconvenient, because they cost in time and
money. Therefore, the use of a prediction model becomes
absolutely necessary. There is a vast number of prediction
models, like: Egli, Longley-Rice, Okumura-Hata, COST 231,
Lee, Bullington, the ITU model P.1546-3, [1], and others. The
literature on this subject is huge, [2-3]. From all the above
models, Longley-Rice is by far the most widely used. There
are commercial software programs for coverage prediction
based on the above mentioned propagation models, but they
are expensive and the use of their demonstration versions is
very restricted. Fortunately, there are some excellent freeware
programs, such as: Radio Mobile (Windows based software)
and SPLAT! (Linux based software). Both of them are based
on the NTIA's original Longley-Rice Technical Note 101
(TN101), [4].
The Radio Mobile program, [5-7], (Radio Propagation and
Virtual Mapping Freeware is based on the Longley-Rice
Model-ITM and uses the 3-arc-second Satellite Radar Terrain
Mission SRTM maps, [8]. Radio Mobile performs a wide
range of simulations, it is user friendly, and can be used
instead of the very expensive commercial applications giving
satisfactory simulation results.
The SPLAT!, [9], program (an RF Signal Propagation, Loss,
And Terrain analysis tool) for the spectrum between 20MHz
and 20GHz is an excellent open-source, Linux based
program. For Windows users, there are two versions, freely
available, [10-11]. SPLAT! is also based on the Longley-Rice
Model-ITM and uses SRTM maps.
In the latest version of SPLAT! ITM is replaced by the
ITWOM, [12-13]. The ITWOM involves empirical data from
ITU-R P.1546 as well as Beer's law and Snell's law and
promises greater accuracy over the older ITM, [13]. An
optimization method for tuning the parameters of ITU-R
P.1546 was recently proposed, [16].
II. MEASUREMENTS AND COMPARISONS
In order to measure the field strength from DVB-T and FM
transmitters, a measurement campaign was carried out in
Thessaloniki, located in the north of Greece. The
measurement equipment consists of a Rohde & Schwarz
FSH-3 portable spectrum analyzer, factory calibrated with ±
0.7dB accuracy, two high-precision calibrated biconical
antennas by Schwarzbeck, SBA 9113 (500MHz - 3GHz) and
BBVU 9135 (30MHz - 1000MHz), a log-periodic precision
calibrated Schwarzbeck antenna USLP 9143 (0.25 – 6 GHz),
factory calibrated with ± 1.0dB accuracy, and low-loss cable
Suhner GX-07272-D, 1.8 meters long with N-type
connectors. In our study, for the calculated values of the
field-strength we employ the Radio Mobile software
(Windows) with ITM, the SPLAT! for Windows software
(splat-1.2.3-win32) with ITM, and the open-source SPLAT!
v.1.4.0 with ITWOM (Linux - Ubuntu 12.10).
A Point-to-Point analysis for Public Greek DTV ERT,
Channel 56 (754MHz) is presented in Table I. Errors between
FSH-3 measurements and ITM model (Radio Mobile &
SPLAT! for Windows), with average error and standard
deviation, are shown in the Table II.
TABLE I
A POINT-TO-POINT ANALYSIS FOR PUBLIC GREEK DTV ERT, CH56 -754MHz.
TABLE II
ERRORS BETWEEN FSH-3 MEASUREMENTS AND ITM MODEL (RADIO
MOBILE & SPLAT! FOR WINDOWS), WITH AVERAGE ERROR AND STANDARD
DEVIATION
Errors between measurements (FSH-3) and simulations
(ITM model from Radio Mobile & SPLAT!), are shown in the
bar graph below in Fig. 1.
Fig.1. Errors between measurements (FSH-3) and simulations with ITM
model (Radio Mobile & SPLAT! for Windows).
The No. 2, 4, 5, 7, 9, and 10 simulations results are better
for Radio Mobile than those of SPLAT! for windows, and No.
1, 6, and 8 simulation results are better for SPLAT! (ITM)
than those of Radio Mobile. The main conclusion for the
above measurement points is that Radio Mobile gives overall
better simulation results with lower standard deviation (S.D. =
3.5 dB) than SPLAT! for Windows (S.D. = 5.5 dB), though
both software use the same propagation model, i.e. ITM.
The sample standard deviation was calculated between
measured path loss values and those predicted by Radio
Mobile and SPLAT! using the following commonly used
equation with Bessel's correction :
N
i
i
x
N
s
1
2
)(
1
1
where :
N: number of measured data points (N=10)
xi: Error between predicted and measured field-strength
(dB) for data point i
μ: Average value of difference (dB)
All the antennas of the FM radio and TV stations are located
on Hortiatis mountain nearby the city of Thessaloniki.
Differences between FSH-3 measurements, SPLAT! for
Windows with ITM and SPLAT! v 1.4.0 for Linux with
ITWOM, with average error and standard deviation, are
shown in Table III. Errors between measurements (FSH-3)
and simulations (SPLAT!-ITM & SPLAT!-ITWOM), are
shown in the bar graph below, Fig. 2.
As we can see from the above measurements and simulation
results, SPLAT! v1.4.0 with ITWOM gives worse simulation
results than SPLAT! for Windows and Radio Mobile.
E(dBμV/m)
No.
DVB-Τ
Measurements
Points
CH56 - 754MHz
LAT: 40.597648
LONG: 23.0997993
LAT
LONG
FSH-3
Measure-
ments
ITM
Radio Mobile
(Windows)
ITM
SPLAT!
(Windows)
ITWOM
SPLAT!
v1.4.0
(LINUX)
1 PROFITIS ELIAS
(7Km/313degs)
40.640411
23.039927 101.6 96.4 99.0 93.8
2 THESSALONIKI
(12,3Km/279degs)
40.615822
22.955735 95.9 97.0 93.9 92.8
3 LAKE VOLVI
(14,3Km/31degs)
40.707102
23.188914 98.9 97.0 92.7 89.5
4 PEREA
(16,7Km/236degs)
40.513489
22.937471 96.7 95.8 91.3 88.4
5 METHONI
(47Km/252degs)
40.469402
22.574711 84.0 84.0 81.7 63.1
6 KORINOS
(52Km/232degs)
40.307130
22.618620 82.3 84.3 80.6 60.6
7 BORDER EVZONI
(68,8Km/321degs)
41.081410
22.588160 65.3 73.8 77.4 58.0
8 SOUMELA
(86Km/256degs)
40.410086
22.116606 75.6 77.2 76.0 56.4
9 LOUTRAKI
(107Km/293degs)
40.966160
21.923630 75.8 77.8 72.8 53.3
10 POLIKASTRO
(69Km/320degs)
41.081190
22.588360 71.9 73.9 77.4 58.0
E(dBμV/m) Errors (dB)
No.
DVB-Τ
Measurements
Points
CH56 - 754MHz
FSH-3
ITM
Radio
Mobile
ITM
SPLAT! For
Windows
FSH-3
& Radio
Mobile
FSH-3 &
SPLAT!
ITM
1 PROFITIS ELIAS 101.6 96.4 99.0 -5.2 -2.6
2 THESSSALONIKI 95.9 97.0 93.9 1.1 -2.0
3 LAKE VOLVI 98.9 97.0 92.7 -1.9 -6.2
4 PEREA 96.7 95.8 91.3 -0.9 -5.4
5 METHONI 84.0 84.0 81.7 0.0 -2.3
6 KORINOS 82.3 84.3 80.6 2.0 -1.7
7 BORDER EVZONI 65.3 73.8 77.4 8.5 12.1
8 SOUMELA 75.6 77.2 76.0 1.6 0.4
9 LOUTRAKI 75.8 77.8 72.8 2.0 -3.0
10 POLIKASTRO 71.9 73.9 77.4 2.0 5.5
Average 0.9 -0.5
Standard Deviation 3.5 5.5
Additionally, in distances bigger than 40Km the simulation
results are much worse. Most probably, SPLAT! with
ITWOM overestimates the attenuation by obstacles and this is
currently under investigation.
TABLE III
ERRORS BETWEEN FSH-3 MEASUREMENTS, SPLAT! FOR WINDOWS WITH
ITM AND SPLAT! V 1.4.0 FOR LINUX WITH ITWOM, WITH AVERAGE ERROR
AND STANDARD DEVIATION
Fig. 2. Errors between measurements (FSH-3) and simulations SPLAT!-ITM
& SPLAT!-ITWOM.
A coverage map produced by Radio Mobile with ITM for
Greek public DTV ERT, Channel 56 (754MHz), is shown in
Fig. 3. The transmitting antenna coordinates are N 40.597648
- E 23.099793, the transmit power is 1.25 kW rms), the
antenna type is a 4 bay-3 directions UHF panel array, each
panel having an 11 dBd gain for a total gain minus cable
losses of 10 dBd, the average antenna height is 70 m, and the
azimuth is 285degs. A coverage map produced by SPLAT! for
the Greek public DTV, ERT CH56 (754MHz), is shown in
Fig. 4.
Fig. 3. Coverage map produced by Radio Mobile with ITM for ERT Ch 56.
Use of 3 directions UHF panel array antenna.
Fig. 4. Coverage map produced by SPLAT! for Windows for ERT Ch 56.
A coverage map produced by SPLAT! v.1.4.0 with
ITWOM is shown in Fig. 5. Because SPLAT! v.1.4.0 works
E(dBμV/m) Errors (dB)
No.
DVB-Τ
Measurements
Points
CH56 - 754MHz
FSH-3
ITM
SPLAT!
For
Windows
ITWOM
SPLAT!
v1.4.0
LINUX
FSH-3
&
SPLAT!
For
Windows
FSH-3 &
SPLAT!
ITWOM
v1.4.0
LINUX
1 PROFITIS ELIAS 101.6 99.0 93.8 -2.6 -7.8
2 THESSSALONIKI 95.9 93.9 92.8 -2.0 -3.1
3 LAKE VOLVI 98.9 92.7 89.5 -6.2 -9.4
4 PEREA 96.7 91.3 88.4 -5.4 -8.3
5 METHONI 84.0 81.7 63.1 -2.3 -20.9
6 KORINOS 82.3 80.6 60.6 -1.7 -21.7
7 BORDER EVZONI 65.3 77.4 58.0 12.1 -7.3
8 SOUMELA 75.6 76.0 56.4 0.4 -19.2
9 LOUTRAKI 75.8 72.8 53.3 -3.0 -22.5
10 POLIKASTRO 71.9 77.4 58.0 5.5 13.9
Average -0.5 -13.4
Standard Deviation 5.5 7.1
only with Linux, Ubuntu 12.10, [14], was used to produce the
coverage map. For the simulation purposes, an omni
transmitting antenna has been used.
Fig. 5. Coverage map produced by SPLAT! with ITWOM model for ERT CH-56.
All measurements were made by varying the receiving
antenna from 0.5 meters to 2.5 meters height and keeping the
peak value. The simulation results produced by ITM &
ITWOM model with Radio Mobile and SPLAT! used the
same reception antenna heights, for an accurate comparison of
results.
Although DAB (Digital Audio Broadcasting), was
developed in the early nineties, it is still not in use in many
countries, [17]. Recently, in February 2013 at Geneva, EBU
released recommendation r138 for Digital Radio Distribution
in Europe [18]. In Greece DAB is currently not in use, and all
radio stations are still analog. There is, however, a necessity
for measurements and predictions in radio broadcasting,
especially in the VHF frequencies. Using the same equipment
and software, as above for the DTV case, measurements were
made for the Greek public FM radio station "ERA-102". This
station is also located on Hortiatis Mountain, nearby the city
of Thessaloniki. The coordinates are the same as before (same
antenna tower), the transmit power is 20 kW, frequency is 102
MHz, the antenna type is 6 bays in 3 directions of FM panel
antennas (dipoles in front of reflector) with a total gain minus
cable losses of 5 dBd, the average antenna height is 50m, and
the azimuth is 285degs.
A Point-to-Point analysis for the Greek public FM radio
station "ERA102" is shown in Table IV. Errors between FSH-
3 measurements and ITM model (Radio Mobile & SPLAT!
for Windows), with average error and standard deviation, are
shown in the Table V.
TABLE IV
A POINT-TO-POINT ANALYSIS FOR THE GREEK PUBLIC FM RADIO STATION
"ERA102"
TABLE V
ERRORS BETWEEN FSH-3 MEASUREMENTS AND ITM MODEL (RADIO
MOBILE & SPLAT! FOR WINDOWS), WITH AVERAGE ERROR AND STANDARD
DEVIATION
Fig.6. Errors between measurements FSH-3 and simulations ITM model,
Radio Mobile & SPLAT!
Errors between measurements (FSH-3) and simulations (ITM
model from Radio Mobile & SPLAT!), are shown in the bar
graph below, Fig. 6. No. 1, 3, 4, 5, and 6 simulations results
are better for Radio Mobile than these of SPLAT! for
windows, and only No. 2, simulation result is better for
E(dBμV/m)
No.
ERA102
Measurements
Points
FM - 102MHz
LAT: 40.597648
LONG: 23.0997993
LAT
LONG
FSH-3
Measure-
ments
ITM
Radio Mobile
(Windows)
ITM
SPLAT!
(Windows)
ITWOM
SPLAT!
v1.4.0
(LINUX)
1 KOURI
(5.2Km/319degs)
40.632814
23.05884 108.8 110.0 100.8 96.6
2 METHONI
(47Km/252degs)
40.469402
22.574711 96.7 91.7 94.0 76.1
3 KORINOS
(52Km/232degs)
40.307130
22.618620 71.9 81.5 92.9 73.0
4 BORDER EVZONI
(68.8Km/321degs)
41.081410
22.588160 63.0 76.3 88.8 70.3
5 LOUTRAKI
(107Km/293degs)
40.966160
21.923630 65.7 76.7 82.7 65.8
6 POLIKASTRO
(69Km/320degs)
41.081190
22.588360 56.1 67.7 88.8 70.3
E(dbμV/m) Errors (dB)
No.
DVB-Τ
Measurements
Points
ERA102- 102MHz
FSH-3
ITM
Radio
Mobile
ITM
SPLAT!
For
Windows
FSH-3
& Radio
Mobile
FSH-3 &
SPLAT!
For
Windows
1 KOURI 108.8 110.0 100.8 1.2 -8.0
2 METHONI 96.7 91.7 94.0 -5.0 -2.7
3 KORINOS 71.9 81.5 92.9 9.6 21.0
4 BORDER EVZONI 63.0 76.3 88.8 13.3 25.8
5 LOUTRAKI 65.7 76.7 82.7 11.0 17.0
6 POLIKASTRO 56.1 67.7 88.8 11.6 32.7
Average 7.0 14.3
Standard Deviation 7.2 16.2
SPLAT! (ITM) than Radio Mobile. Consequently, Radio
Mobile gives better simulation results with a lower standard
deviation (S.D. = 7.2dB) than SPLAT! for Windows (S.D.=
16.2 dB), though both software use ITM for propagation
modeling. It can be also seen in the FM case that the
simulations results produced by SPLAT! for Windows are
worse than Radio Mobile results, and getting worse as
distance increases above around 40Km. The simulation results
are, in general worse for VHF FM radio frequencies than
those for UHF DVB-T frequencies.
Differences between FSH-3, SPLAT! for Windows with
ITM and SPLAT! v 1.4.0 for Linux with ITWOM, with
average error and standard deviation , are shown in Table VI.
Errors between measurements (FSH-3) and simulations
(SPLAT!-ITM & SPLAT!-ITWOM), are shown in the bar
graph below, Fig. 7.
TABLE VI
ERRORS BETWEEN FSH-3, SPLAT! FOR WINDOWS WITH ITM AND SPLAT! v
1.4.0 FOR LINUX WITH ITWOM, WITH AVERAGE ERROR AND STANDARD
DEVIATION
Fig.7. Errors between measurements FSH-3 and simulations SPLAT!-ITM &
SPLAT!-ITWOM.
It can be noticed that simulation results for No. 3 4, 5, and 6
measurement points using SPLAT! with ITWOM are better
than SPLAT! for Windows, which in turn gives better results
for No. 1 and 2 measurement points. We observe that for
frequencies in the VHF FM range, SPLAT! with ITWOM
gives better simulation results than SPLAT! for Windows.
A coverage map produced by Radio Mobile (ITM Model)
for Greek public FM radio "ERA-102" is shown in Fig. 8. A
coverage map produced by SPLAT! for Windows (splat-1.2.3-
win32) for the Greek Public FM Radio Station, "ERA-102" is
shown in Fig. 9.
Fig. 8. Coverage map produced by Radio Mobile with ITM for "ERA-102" -
FM radio station.
Fig. 9. Coverage map produced by SPLAT!-ITM (Windows), for "ERA-102".
E(dbμV/m) Errors (dB)
No.
DVB-Τ
Measurements
Points
ERA102- 102MHz
FSH-3
ITM
SPLAT!
For
Windows
ITWOM
SPLAT!
v.1.4.0
Linux
FSH-3 &
SPLAT!
For
Windows
FSH-3 &
SPLAT!
v.1.4.0
Linux
1 KOURI 108.8 100.8 96.6 -8.0 -12.2
2 METHONI 96.7 94.0 76.1 -2.7 -20.6
3 KORINOS 71.9 92.9 73.0 21.0 1.1
4 BORDER EVZONI 63.0 88.8 70.3 25.8 7.3
5 LOUTRAKI 65.7 82.7 65.8 17.0 0.1
6 POLIKASTRO 56.1 88.8 70.0 32.7 14.2
Average 14.3 -1.7
Standard Deviation 16.2 12.7
A coverage map produced by SPLAT! v.1.4.0 with ITWOM
for the same radio station is shown in Fig. 10.
[4] P.L. Rice, A.G. Longley, K.A. Norton, and A.P. Barsis. “Transmission
loss predictions for tropospheric communications circuits”, Technical
Note 101, revised 1/1/1967, U.S. Dept. of Commerce National
Telecommunications & Information Administration, Institute for
Telecommunications Sciences(NTIA-ITS).
[5] Roger Coudé, Webpage of Radio Mobile,downloads and How to
http://www.cplus.org/rmw/english1.html, Freeware by VE2DBE.
[6] Webpage of G3TVU about Radio Mobile : applications and
possibilities.http://www.g3tvu.co.uk.Radio_Mobile.htm.
[7] Salamanca L. Murillo-Fuentes J.J. Olmos P. “ Review of the Radio
Mobile Software as a teaching tool for Radio planning” IEEE
multidisciplinary engineering education magazine, vol. 6, no. 2, June
2011.
[8] NASA, “Shuttle Radar Topography Mission data”. Available on line at
http://www2.jpl.nasa.gov/srtm/
[9] Magliacane J. SPLAT! An RF Signal Propagation, Loss, And Terrain
analysis tool for the spectrum between 20 MHz and 20 GHz. Available
on line. http://www.qsl.net/kd2bd/splat.html.
[10] McMellen, J. RF propagation modeling with SPLAT !for windows.
Available on line. http://blog.gearz.net/2007/09/rf-propagation-
modeling-with-splat-for.html.
[11] Austin W. RF propagation modeling with SPLAT !for windows.
Available on line. http://www.ve3ncq.ca/wordpress/?page_id=62.
[12] Sid Shumate, ‘Deterministic Equations for Computer Approximation of
ITU-R P.1546-2’, International Symposium on Advanced Radio
Technologies and The Working Party Meetings for ITU-R WP3J,3K,3L
and 3M hosted by National Institute of Standards and Technology, June
2/4, 2008.
[13] S.E. Shumate. ‘Longley-Rice and ITU-P.1546 combined A new
international terrain-specific propagation model’. In Vehicular
Technology Conference Fall (VTC 20102-Fall), 2010 IEEE 72nd, Sept,
2012.
Fig. 10. Coverage map produced by SPLAT!-ITWOM (Linux), for FM radio
station "ERA-102". [14] Ubuntu 12.10. Available on line. http://www.ubuntu.com.
[15] F. Perez-Fontan. J.M. Hernando-Rabanos, “Comparison of irregular
terrain propagation models for use in digital terrain data based
radiocommunication system planning tools”. IEEE Transactions on
Broadcasting, Jul. 1995.
III. CONCLUSION
[16] K.Paran, N. Noori. “Tuning of the propagation model ITU-R P.1546
recommendation”. Progress In Electromagnetics Research B, Vol. 8,
243-255, 2008.
The Longley-Rice (ITM) model, that Radio Mobile and
SPLAT!, use in conjunction with worldwide Shuttle Mission
Satellite Radar 3-arc-second data (SRTM) produce, in some
cases, big differences comparing with measurements results.
The ITM does not work quite well in the line-of-sight mode
and in the early diffraction range. Furthermore, the ITM does
not use more detailed terrain information as other more
sophisticated models do, [15]. The ITWOM propagation
model was recently proposed, [13], claiming an improved
accuracy over the ITM. However, early simulations and
measurements results in point-to-point path analysis with
ITWOM do not verify these claims. The ITWOM has a
somewhat better accuracy for distances < 20Km, but very big
differences for larger distances > 40Km. Of course, we were
not able to use the more detailed 1/3-arc-second SRTM maps,
because they are only available for the US territory.
[17] W.Fischer “Digital Video and Audio Broadcasting Technology”. A
Practical Engineering Guide, Third Edition, Springer.
[18] http://tech.ebu.ch/docs/r/r138.pdf.
ACKNOWLEDGMENT
Parts of this work are funded by NATO SfP project ORCA
(984409).
REFERENCES
[1] ITU-R, “Method for point-to-area predictions for terrestrial services in
the frequency range 30MHz to 3.000 MHz (p.1546-3),” 2007.
[2] T.Rappaport, “Wireless Communications: Principles and Practice”.
Prentice Hall, 2002.
[3] J.S. Seybold. “Introduction to RF Propagation”, John Wiley & Sons, Inc,
2005.
