IEEE INTERNATIONAL SYMPOSIUM ON BROADBAND MULTIMEDIA SYSTEMS AND BROADCASTING 2014 1

Studying Digital Terrestrial TV coveragePablo Flores Guridi, Member, IEEE, Andres Gomez Caram, Agustın Labandera, Gonzalo Marın and Marıa

Simon, Senior Member, IEEEFacultad de Ingenierıa, Universidad de la Republica, Uruguay.

Email: {pablof, agomezca, labandera, gmarin, maria}@fing.edu.uy

Abstract—This article presents the development of numericalmodels to simulate the propagation of the TV signal, and aset of measurements of the electromagnetic signal to adjust themodels. These tools have been devised to help in the deploymentof digital television, ISDB-Tb standard, in Uruguay. The aim isa country coverage as wide as possible. A good estimation ofthe signal propagation shall be used to choose the best placesfor transmitters, the transmission modes and to give guidelinesfor reception antennas installation. The implemented models,which are well known, are briefly described. The measuringmethod is more thoroughly described as there is no establishedprocedure and the spectrum analyzer’s settings are discussed.Spatial validation, using neighbouring points is proposed. Themeasuring method is validated both by its coincidence with theFriis formula for free space propagation, when this conditionarises, and by the consistency between neighbouring points.Okumura-Hata and Recommendation ITU-R P.1546-4 models arewell suited for coverage prediction in Montevideo using certainparameters that are justified in the article. The statistical analysisof the set of data issued from the campaign is presented anddiscussed.

Index Terms—Propagation, coverage, channel modeling andsimulation.

I. INTRODUCTION

URUGUAY has adopted in 2011 the ISDB-Tb digital tele-vision standard for open free diffusion, as did the major-

ity of the South American region. The public TV broadcasteris already emitting a pilot signal, and the frequency assignationfor commercial, public and community channels was alreadydefined. However, the experience about propagation of theopen TV signal is yet recent and scarce in the region. Thegeographical and demographic conditions are very differentfrom Japan, and also are the building materials.

A good estimation of the signal propagation, regarding thereceived power, interferences and noise immunity, shall beused to choose the best places for transmitters, the trans-mission modes, and to give guidelines for receiving anten-nas installation. To achieve this goal, a software simulationpackage was developed, based on previous work which wasfirst intended for GSM signals. It includes different welldocumented models, suitable for broadcasting signals in theUHF band, in particular Okumura-Hata and RecommendationITU-R P.1546-4. Due to the fact that Okumura-Hata does notcontemplate terrain characteristics, its prediction is simplerthan that from ITU-R P.1546-4. It is appropriate for a roughview of signal levels in the city, in contrast with ITU-R P.1546,

This work was funded by Agencia Nacional de Investigacion e Innovacion(ANII), Uruguay. Official website: http://www.anii.org.uy.

which returns a more detailed output, expressed out in lessregular patterns.

In order to register the ISDB-Tb signal levels in Montevideoand to compare its values with the models prediction, ameasurement campaign was planned and carried out.

The received signal power was measured using a standardhandheld spectrum analyzers. Several bibliography suggestusing different types of detectors. Its selection regardingaccuracy and robustness is discussed in this article.

The Uruguayan authorities have established 51 dBµV/m asthe electric field strength value that a channel must achieve inthe border of its coverage area. Its laboratories are testing thereceivers to be authorized, whose sensitivity is also specified.The relationship between those values is a key factor when itcomes to planning the emitter’s location, height and power.

In Section II the numerical models and its software imple-mentation are presented.

The campaing is described in Section III, in which themeasurement methods are also discussed. A protocol wasdesigned to improve the reliability of the collected data, basedin the consistency between neighbouring sites, which is alsodescribed in Section III.

The collected data are analyzed in Section IV, payingattention to coincidences and discrepancies between modelsand measurements. A very reasonable fitting with known andadjusted models is obtained, which proves that the softwaresimulation package is correctly implemented.

In Section V, broad guidelines for this kind of evaluationare given.

II. NUMERICAL MODELS AND SOFTWARE PACKAGE

A. Free-Space Path Loss

Consider a signal transmitted through free space to a re-ceiver located at a distance d from the transmitter. Assume theare no obstacles nearby to cause reflection, diffraction or scat-tering; so the signal propagates along a straight line betweenthem: the channel model associated with this transmission iscalled line-of-sight (LOS) [1]. The ratio between the powertransmitted and received is given by the simplest form of theFriis transmission equation [2],

Pr

Pt= Gt.Gr

[λ

4πd

]2, (1)

where Gt and Gr are the transmitter and receiver antenna fieldradiation patterns in the LOS direction. This equation showshow the attenuation of the signal increases with the square

IEEE INTERNATIONAL SYMPOSIUM ON BROADBAND MULTIMEDIA SYSTEMS AND BROADCASTING 2014 2

of the distance d and decreases with the square of the carrierwavelength λ.

However, most broadcasting systems operate in complexpropagation environments that can not be modelled by free-space path loss. Several path loss models have been developedthroughout the years to predict signal levels in rural, urbanand suburban areas. All of them differ in how they approachshadowing, fading, diffraction, reflection and scattering of thesignal. In this paper only two of them will be discussed, withan special focus on Recommendation ITU-R P.1546-4.

B. Empirical and Semi-Empirical Path Loss Models

These models are mainly based on empirical measurementsperformed at different distances from the transmitter, fordifferent frequencies and environments, usually significantlydifferent from those in which the models are going to beapplied. Therefore, models must be analyzed and tuned fordifferent regions and environments, which implies the need oftaking measurements for verifying, adjusting or even discard-ing each model. Anyway, its original versions can be used asguidelines.

1) Okumura Model: This model was developed empiricallyin 1970s by Okumura [3] with data measured throughout thecity of Tokyo, Japan. This model was developed to work withfrequencies ranging 150 MHz to 1500 MHz, transmittingantennas’ height between 30 m and 100 m, mobile stationantennas between 1 m and 10 m, and link distances greaterthan 1 km and lower than 100 km [1]. It was first conceivedfor analogical cellular networks.

2) Hata Model: The Hata [4] model for urban areas, alsoknown as Okumura-Hata, is an empirical formulation of thegraphical path loss data provided by Okumura. It takes asinput the environment (urban, suburban or rural areas), thefrequency of the carrier, the distance between transmitter andreceiver, the height of the base station antenna and the heightof the mobile reception antenna.

Because of its simplicity, it is natural to choose Okumura-Hata as prime model to get a first approach of the propagationof the TV signal. Anyway, since terrain data are not consid-ered, several factors as terrain clearance angle corrections ortropospheric scattering are shelved.

3) Recommendation P.1546-4: This recommendation pro-vides a method for point-to-area propagation predictionsfor terrestrial services in the frequency range 30 MHz to3000 MHz. It is intended for use on tropospheric radiocircuits over land paths, sea paths and/or mixed land-sea pathsbetween 1−1000km length for effective transmitting antennaheights less than 3000 m. The method is based on inter-polation/extrapolation from empirically derived field-strengthcurves as functions of distance, antenna height, frequencyand time and locations percentages. The calculation procedurealso includes corrections to the results obtained from thisinterpolation/extrapolation to account for terrain clearance andterminal clutter obstructions [5].

The Recommendation ITU-R P.1546-4 takes as an input asurrounding representative parameter that can be either urban,dense urban or suburban area. This parameter must be set

for every environment in which the prediction is done, soempirical data should be collected and analyzed.

C. Implemented Software

Specific software was implemented in order to compareand eventually adjust the above propagation models withdigital terrestrial TV signal actual propagation. It is fed withgeographical information and calculates the field strengthor the received power in every desired area according toboth the transmitting and receiving antennas characteristics,which can use either default or custom radiation patterns, andthe transmission parameters, such as the transmitter effectiveradiated power (ERP) or the propagation path and surroundingcharacteristics, for each path loss model.

This software was used to predict the emission of the na-tional television network signal field strength in some specificlocations in Montevideo, Uruguay. Free-space path loss modelwas used, then, also Okumura-Hata and RecommendationITU-R P.1546-4. These models performance was then com-pared with data collected during a measurement campaign,described in Section III. Finally, the model which best fits thecity’s conditions was selected and the best parameters for itenvironment were chosen.

III. MEASUREMENT CAMPAIGN

A. Planning

In order to acquire the ISDB-Tb signal levels in Montevideoand to compare its values with the models predictions, ameasurement campaign was planned and carried out. Themeasured signal was the emission of the national televisionnetwork (Television Nacional Uruguay: TNU). The measure-ment points were chosen according to distance and positionrelative to the transmitting antenna, as well as terrain andurban characteristics, in order to sweep the whole urban area ofMontevideo. For that purpose, 7 radials were traced accordingthe cardinal points. Depending on the radial lenght, a setlocations were chosen, as it is shown in Figure 1.

The measurement of TV electromagnetic field was better inopen places; dense urban zones give very variable results as aconsequence of reflection and diffraction effects.

The received signal power was measured using a standardhandheld spectrum analyzer that had been compared with veryaccurate instruments. Measurement of OFDM signals presentsmany difficulties because of its high peak factor. RMS, sampleand min/max envelope detectors, usually found in spectrumanalyzers, throw different results. Several bibliography suggestusing different types of detectors, but after extensive laboratorystudies, RMS was chosen as the adequate detector.

B. Measuring method

The measurement of RF signals is a highly complex taskdue to the many variations and effects of stochastic natureinfluencing the signal. Given this, it was considered that wasnot enough to make a single measurement for each location,but would be useful to have several measurements to comparebetween each other and then reach a unique representative

IEEE INTERNATIONAL SYMPOSIUM ON BROADBAND MULTIMEDIA SYSTEMS AND BROADCASTING 2014 3

Fig. 1. Measurement points for urban and suburban areas of Montevideo. Source: “Montevideo” 34◦52′35.14′′S and 56◦11′12.08′′W . Google Earth.October 13, 2013.

value. Very similar values indicate a reliable measure. In thisway it would be possible to be free of destructive effects suchas multipath fading or reflections, which can affect a specificpoint but can not always affect the others.

This also presents advantages when comparing with predic-tions made with ITU-R P.1546-4. It was noted that predictionsmade using reception height values of a few meters can presentconsiderable differences in signal power in places just a fewmeters away. This makes it possible to detect these signaldrops in a location.

The procedure used was baptized Method of the FourCorners. It involves taking a measurement at each corner ofthe block to which it belongs the location chosen. This methodgave highly satisfactory results.

C. Results

Several weeks were required to carry out the measurementcampaign. A total of 88 measurements were taken in 26 dif-ferent locations. For each measure, the geographic coordinatesand the signal level were obtained. In most cases measureswere taken at the four points planned, except in those wherewas not a defined block or it had no four corners. In thesecases, two or three measurements were taken depending tothe case.

IV. DATA PROCESSING AND ANALYSIS

As a result of the measurement campaign, 88 points weremeasured from a total of 26 locations. Before doing any furtheranalysis, it was necessary to remove outliers from the data.

A. Measurements Selection Criteria

In order to achieve this, quantitative and qualitative criteriabased on a series of characteristics of the measured signal weredeveloped. Some of the aspects taken into account were:

1) Channel spectrum shape.2) Location characteristics: foliage, buildings, structures

and traffic.3) Signal level and dispersion among measurements in the

same location.4) Line of sight with the transmitting antenna.After applying these criteria to the dataset, two locations

were discarded, obtaining a preliminary group of twenty fourlocations. Two locations with line of sight (LOS) to thetransmitting antenna were chosen in order to validate themeasurement procedure. Location SO3 is situated on top ofCerro de Montevideo (the city’s highest hill) and shows analmost theoretical free space loss condition. The similaritybetween the link budget considering free space loss and thepower measured proved the measuring method to be valid.Similarly, location SO2 is situated near the bay and, despitebeing in front of the transmitting antenna, is slightly obstructedby trees, so the result differs from the calculated value. Bothlocations had to be removed from the propagation modelsanalysis because they do not meet the model’s hypothesis.Hence, a final subgroup of twenty two locations was created.In Figure 2 the comparison between these measured valuesand the Friis transmission equation applied to the locationscan be seen.

B. Comparison Among Measurements and PredictionsWhen the results from the different models and the mea-

sured points were compared, several issues had to be pointedout.

1) Free space loss represents an upper limit for receivedsignal strengh.

2) From the different ITU-R P.1546-4 types of environ-ment, suburban should be used.

3) Results considering ITU-R P.1546 considering 50% and90% of the time are very similar.

IEEE INTERNATIONAL SYMPOSIUM ON BROADBAND MULTIMEDIA SYSTEMS AND BROADCASTING 2014 4

-80

-70

-60

-50

-40

-30

-20

-10

Location

Prx

(dB

m)

ON

O6

SO

1

NE4

S4

NO

6

E4

SE1

NO

1

NE1

S5

E1

S3

NO

2

SE3

NE5

SO

6

E2

SO

5

ON

O5

E6

NO

3

NO

4

Measurement

Free Space Loss

Okumura-Hata

P.1546 90/50Suburban

Fig. 2. Comparison between measurements and models for the 22 locations subgroup.

4) Okumura-Hata does not consider the effect of big slopesin the terrain, while ITU-R P.1546-4 does but overesti-mates its effects (as seen in locations SO5 and SO6).

5) Locations near the transmitting antenna such as NO6may be affected by multipath constructive interference,resulting in high signal power.

In order to improve Okumura-Hata’s performance, a newset of parameters adjusted to this dataset was proposed. It wasdone according to Lee’s formula [6] [7]:

A+B log d (2)

Iterative cross-validation was used to estimate the parame-ters with linear least square method.

The calculated mean error and the standard deviation of theerror for the proposed models are shown in Table I.

Model Zone Mean error Error σ2

(dB) (dB)ITU-R P.1546-4

50% time Suburban 0.73 9.5950% locations

ITU-R P.1546-490% time Suburban 0.24 9.64

50% locationsStandard OH Urban 1.12 9.3Adjusted OH - 2.77 6.99

TABLE ICOMPARISON BETWEEN RESULTS OBTAINED WITH THE NEW ADJUSTED

MODEL, OKUMURA-HATA AND ITU-R P.1546-4.

As seen in the table, the proposed values do not presenta significant improvement in the perfomance of the model asit improves the deviation of the error but shows bigger meanerror. In addition, both ITU-R P.1546-4 perform better thanOkumura-Hata in mean error and similarly in error deviation.

V. CONCLUSIONS

Even though some references advise to use the spectrumanalyzers with its min/max or sample values detectors, RMSmeasurement has proven to be more stable and expressiveregarding the power density of OFDM signals.

The implemented mathematical models fit with the mea-sured data in three typical cases: when there is direct visionbetween transmitter and receptor, the Friss formula gives thegood prediction; in medium reception zones both Okumura-Hata and ITU-R P.1546 perform well; and when the signal isweak, obstacles are present and diffraction is important, ITU-R P.1546 gives the better prediction, being in the pessimistic(and then conservative) side.

The parameters to be selected in ITU-R P.1546 are, at leastfor Montevideo and very probably for Uruguay, sub urban typeand terrestrial path.

ACKNOWLEDGMENT

The authors would like to thank the collaboration of UR-SEC, the Uruguayan Regulatory Body, for their participationin the measurement campaign and for calibration of instru-ments.

REFERENCES

[1] A. Goldsmith, Wireless Communications, Cambridge University Press,2005.

[2] H. T. Friis, A Note On A Simple Transmission Formula, Proc. IRE, vol.34, p. 254, 1946.

[3] Okumura, Yoshihisa, et al. Field strength and its variability in VHF andUHF land-mobile radio service. Rev. Elec. Commun. Lab 16.9 (1968):825-73.

[4] Hata, Masaharu. Empirical formula for propagation loss in land mobileradio services. Vehicular Technology, IEEE Transactions on 29.3 (1980):317-325.

[5] International Telecommunication Union, Recommendation ITU-R P.1546-4, 2009.

IEEE INTERNATIONAL SYMPOSIUM ON BROADBAND MULTIMEDIA SYSTEMS AND BROADCASTING 2014 5

[6] W. C. Y. Lee, Lee’s Model a condensed version shown in AppendixII, written by the Propagation Ad Hoc Committee of IEEE VehicularTechnology Society appeared in a special issue of IEEE Transactions onVehicular Technology, February 1988. pp. 68-70.

[7] W. C. Y. Lee Mobile Cellular Telecommunications Systems, McGraw HillCo., Chapter 4.

Pablo Flores Guridi has obtained his Electrical Engineering degree in 2012at Universidad de la Republica, Uruguay. He is currently working in hismaster thesis which is related with the work described in this article. Hismain academic interest is digital television.

Andres Gomez Caram is a student of Electrical Engineering in the Univer-sidad de la Republica, Uruguay. He participated in the current work duringhis degree final project.

Agustın Labandera is a student of Electrical Engineering in the Universidadde la Republica, Uruguay. He participated in the current work during hisdegree final project.

Gonzalo Marın is a student of Electrical Engineering in the Universidad dela Republica, Uruguay. He participated in the current work during his degreefinal project.

Marıa Simon is Electrical Engineer and Full Professor at Uruguay’s publicuniversity, Universidad de la Republica, in the field of Telecommunications.Her academic interests, in the field of Telecommunications, include Informa-tion Theory, Signal Coding and Data Networks, especially traffic studies. Sheis working also in Digital Television.

She has been Minister of Education and Culture between 2008 and2011 and President of the Board of ANTEL (National Administration ofTelecommunications, public company) between 2005 and 2007. From 1998to 2005 she has been Dean of the School of Engineering, Universidad de laRepublica.