# Handheld Digital TV Performance Evaluation Method

Authors: Gunnar Bedicks; Fujio Yamada; Francisco Sukys; Cristiano Akamine; Luis Tadeu Raunheitte; Edson L. Horta
Journal: International Journal of Digital Multimedia Broadcasting
 (2008)

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## Abstract

This paper presents a simplified method for signal level clearance evaluation in each place of signal reception up to threshold for a given portable TV receiver device. It describes briefly the structure of transmission system considering the “1Seg” structure of ISDB-T. The preliminary laboratory test was made before the field tests to verify the main features of handheld receiver.


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## Body

## 1. Introduction

The new generation of handheld devices
predicts that the consumption and use of mobile and portable television sets will
change our habits as the use of cellular phones revolutionized the
telecommunication business. People enjoy having in the video receiver information
about news, sports, weather, traffic conditions and shows at anytime and
anyplace without any access restrictions. The handheld device manufacturer desires
to evaluate the performance of the product, for each environment, before sending
it to the market. Usually, handheld devices circuits are compact and have no
access inside the circuitry to connect measurement instruments. This work
presents a simplified method to evaluate the device performance data and the
level clearance (how much the signal would degrade and still have a good reception).
This method can be useful for broadcaster to test the performance of its system
and the portable receiver.The main transmission systems
possibilities to provide live television services on handheld devices currently
available are as follows: T-DMB, S-DMB, Media FLO, DVB-H, and ISDB-T, all of
them using OFDM modulation.Digital video broadcasting handheld (DVB-H)
uses a time-sliced transmission scheme allowing turn the receiver circuit off, for
those time slices that are not of interest to the user and thus reducing the
power consumption used for TV reception. A significant advanced feature is the
H.264/AVC coding providing efficient coding. The optional multiprotocol encapsulation
(MPE)FEC offers a solid error protection [1, 2].Media following link only (Media FLO)
is able to dispose 15 to 20 channels of real time broadcast TV displayed on a
mobile phone at 30 frames per second scanning in HD resolutions. It uses
hierarchical modulation supporting multiple channels of live contents and
downloaded clips and forward error corrector techniques. It uses H.264 video
coding and audio AAC coding [3, 4].Digital multimedia broadcast (T-DMB)
delivers mobile television services based on the Eureka-147 digital audio broadcast
(DAB) standard with additional error correction code offering a capability of
12 to 15 Mbps, using the bandwidth of 1.536 MHz for mobile digital TV reception [5].Integrated
services digital broadcast terrestrial (ISDB-T) provides one mode suitable to
broadcast to handheld devices named “1Seg” transmission. The 6 MHz channel band
is divided into 13 segments of 430 kHz bandwidth each and one of them can be
suited for portable digital TV reception. This method is known as band-segmented
transmission OFDM (BST-OFDM) in same way of DVB-H system. For one segment, it is
used transmission H.264 encoder, providing a higher digital compression rate
than MPEG-2. Also, the QPSK modulation scheme associated to OFDM allows strong
robustness against the multipath, burst noise and Doppler effect even in lowC/N. ISDB-T allows up to three simultaneous transmission
layers in the same bandwidth. As well, a modulation method with different
robustness degree can be selected for each layer [6, 7].This paper describes the procedure
for evaluation the clearance that exists in each place of digital signal reception.
A field trial was carried out in São
Paulo
to determine the viability of the proposed
method using mobile devices with “1Seg” ISDB-T transmission. A 1 kW transmitter tuned
on channel 24 (530 ~ 536 MHz) was installed with a 100 meter height tower. The
modulation scheme was configured to have twelve segments for HDTV transmission
and one segment for broadcasting to handheld receivers. Several reception sites
distributed in main regions of the city were selected to evaluate the reception
signal quality.


## 2. Background

The band-segmented transmission (BST)-OFDM
modulation scheme used in ISDB-T system was developed to broadcast digital
terrestrial TV with flexible modulation. It is something similar to
hierarchical transmission used in DVB-H. The main difference is that in
BST-OFDM, the 6 MHz channel bandwidth is divided into 13 segments, grouped in up
to three hierarchical levels, with different modulation configuration and
robustness. Brazil
adopted the system ISDB-T modified, using H264 code instead of MPEG-2. With
this structure, it is possible to transmit one HDTV signal with 64-QAM scheme,
one program for vehicular reception in 16QAM, and one segment in QPSK. It was
used in this test the 1Seg transmission structure modulated in QPSK together
with a HDTV transmission using 12 segments.The OFDM concept is based on
spreading the data to be transmitted over a large number of carriers, each being
modulated at a low bit rate. There is no interference between carriers, even
with a degree of spectral overlap because the carrier spacing is selected so
they are orthogonal over the symbol period, and thus, the symbol can be recovered
without degradation [7].For maximum spectral efficiency, the
carrier spacing is equal to the reciprocal of the symbol period. The multiplex of the carrier
may be conveniently generated digitally using the inverse fast Fourier transformer
(IFFT) process.The carrier spacing in OFDM system is
inversely proportional to the symbol length to achieve the orthogonality, for this
reason, the number of carriers in a channel is determined from the symbol
length. In order to obtain reasonable useful bitrate, a guard interval is used
to remove the effect of intersymbolic interference.


## 3. Preliminary Laboratory Test

The aim of this step was to verify the
performance of the handheld devices sold in regular commerce. For the test, it was
used an ISDB-T one segment receiver.  These
types of apparatus have no available facilities to access inside circuits to be
measured. So, it was necessary to develop an expedient to get these data
without changing the receiver characteristics. The alternative was to fasten
the handheld receiver antenna close to a spectrum analyzer antenna used to measure the field strength of the TV channel signal searched (Figure1). For
this purpose, the antenna installed in the spectrum analyzer was constructed to
be similar to that used in the handheld device, considering that both antennas were
capturing just the same signal strength. To avoid nondesired disturbance, the
handheld receiver and the spectrum analyzer were installed inside a Faraday
cage.Figure 1
Laboratory installation.The transmission signal was generated
by a broadcast tester generator modulated by one HDTV signal using 12 segments
and a handheld signal using only one segment with H264 coder and configured in
a strong scheme as QPSK constellation, guard interval 1/16, FEC 1/2, temporal interleaver
0, 4 seconds, and 330 Kbps bitrate. This signal was radiated inside the Faraday
cage by an antenna free of the external disturbance.Figure2 summarizes the handheld
features measurement setup. The spectrum analyzer and receiver antennas,
assembled together in parallel, pick up same field intensity level. The
attenuators allow adjusting the level for desired value. The following main
features were measured.Figure 2
Handheld feature measurement setup.(i) Minimum Signal Level
The attenuator was adjusted to have a level of
about −40 dbm measured by spectrum analyzer within
the “one segment band” (430 kHz). Gradually, the signal level was reduced until
the image freezes, reaching the limit of perceptibility (LOP).  Table1 shows the results obtained.Table 1
Feature of handheld sample.
FeatureHDTVHandheldMinimum signal level−71.3 dBm−82.4 dBmC/N (Carrier to Noise)18 dB2.7 dBMultipath (Brazil  D)11.6 dB11.6 dB(ii) Carrier to Noise Ratio at the Limit of Perceptibility (LOP)
The signal level (C) was adjusted to
about −40 dBm. After that,
it was injected additional Gaussian noise (N) up to the image locks. Table 1
indicates the calculated C/N value in dB(iii) Multipath Interference
It was injected a signal generated by
channel emulator configured to reproduce the “Brazil D” multipath spectrum,
composed by 5 signals delayed from the main signal. Note that “Brazil D”
represents a typical indoor reception configuration. The carrier signal level
(C) was adjusted to −40 dBm and then it was injected additional Gaussian noise
(N) until the image reached the LOP. The C/N calculated value is presented in
Table 1.


## 4. Field Test Procedures

The aim of this test was to evaluate in
the field the behavior of a handheld device using a simplified  procedure and, at the same time, to verify
the signal level clearance available for this receiver. The results presented here
are only samples of the test procedure, but not necessarily a conclusion. For
this test, it was used a one segment handheld TV receiver sold in Japan  commerce.As the users of mobile devices are in
movement, the signal arriving in the apparatus depends on conditions, like
place where they are at each moment, existence of buildings, presence of the
people, the direction that the device antenna is pointed to, and the height of
the device antenna. Besides, because the researcher needs to move between
crowds, the measurement setup must be simple and flexible allowing easy
transport. So, taking simplicity as a goal, the equipment suited for use at the
field was a portable spectrum analyzer aggregated to the handheld receiver as
shown in Figure3.Figure 3
Field test setup.As the field strength for mobile
devices is very instable; the measurements must be repeated in the same place,
varying the antenna point out direction to evaluate the average value. The
number of selected test points must represent the morphology of a large city in
real signal propagation conditions.Figure4 shows the transmission test setup
broadcasting one HDTV program with 12 segments and one program for handheld
receiver using one segment, in the same 6 MHz channel. The modulation for “one
segment” was QPSK. It was used an 1 kW transmitter with omni antenna, tuned to
channel 24 (533 MHz). A band pass filter was used to restrict the noise to a
band near the value of the “one segment TV” band, necessary to not overload the
transmitter power amplifier.Figure 4
Transmission setup.In summary, the field test procedures
to evaluate the signal clearance are as follows.(i)
Adjust the transmitter to radiate one segment
program.(ii)
Measure the signal levelC (dBm) for one
segment band in the transmitter side (point B—Figure 4).(iii)
Install the handheld receiver together with
the spectrum analyzer in each selected site. Measure the received signal level,C1 (dBm).(iv)
In the transmitter side, inject gradually the Gaussian
noise varying the noise attenuator up to the receiver locks. Read the value of
the injected noiseNj(Tx) in dBm (point C—Figure 4).(v)
Repeat the above
procedures for other measurements at same site, changing the antenna
directions, rotating of90° each time [8] to found the signal
average value.


## 4.1. Signal Clearance Calculation Procedure

### 4.1.1. Definition

The clearance is defined as(1)10log(NNa)dB,where N=noisepower within the one
segment band (430 kHz) that makes the receiver reach the limit of perceptibility
(LOP), Na= interfering noise power at the
receiver input in one segment band (430 kHz).


### 4.1.2. Signal Clearance Calculation

(i) As measured in laboratory, the LOP reference noise
in the receiver for channel configuration used is 2.7 dB below the signal level
inputC1 (dBm) (see Table 1).
So,(2)N(dBm)=C(dB)−X(dB),where X(dB)=C/N=2.7dB (from Table 1).(ii) When the receiver reaches LOP(3)N=Na+NjorNa=N−Nj,where Nj= equivalent
noise injected, at the receiver side, over the interfering noise power Na(4)Nj=Nj(Tx)k,where
Nj(Tx) was converted from Nj(Tx) dBm
into power unit, k= attenuation factor and may be
calculated as
(5)k=C(Tx)C1,where C(Tx)= power injected
into the one segment band at the transmitter side (measured) converted from C(Tx) dBm;  C1= input power at the receiver
device.(iii) By using clearance definition(6)MdB=10log(NNa),
from (3)(7)Na=N−Nj,
and from (4)
(8)Nj=Nj(Tx)k,so,
(9)MdB=10log(NN−Nj(Tx)/k),where k is obtained from (5).The transmitter signal level at the
point B (see Figure4) was fixed at −27 dBm. The
variable Gaussian noise Nj(Tx) injected at the point C (see Figure 4) is
exhibited in the Table 2.Table 2
Field measurement results.
PointN°DistNj(Tx)Average SignalC1Max. SignalClearance*KmdBmdBmdBmdB12−30.91−75.7−73.15.822−30.11−72.5−71.19.632−30.62−77.9−76.16.842−30.33−63.5−61.18.152−30.43−52.5−51.17.662−30.71−71.1−69.16.575−30.57−52.2−51.07.085−30.81−81.3−81.66.195−29.81−73.4−71.013.3105−29.81−65.7−64.013.31110−30.43−88.0−88.07.6With the data collected in the field,
the level clearance was calculated according to the procedure described above.
The clearance value means what is the signal level tolerance, existing in each
site to keep the reception in a good condition. This clearance level depends on
the signal level and the noise level that exist in each point.


## 4.1.1. Definition

The clearance is defined as(1)10log(NNa)dB,where N=noisepower within the one
segment band (430 kHz) that makes the receiver reach the limit of perceptibility
(LOP), Na= interfering noise power at the
receiver input in one segment band (430 kHz).


## 4.1.2. Signal Clearance Calculation

(i) As measured in laboratory, the LOP reference noise
in the receiver for channel configuration used is 2.7 dB below the signal level
inputC1 (dBm) (see Table 1).
So,(2)N(dBm)=C(dB)−X(dB),where X(dB)=C/N=2.7dB (from Table 1).(ii) When the receiver reaches LOP(3)N=Na+NjorNa=N−Nj,where Nj= equivalent
noise injected, at the receiver side, over the interfering noise power Na(4)Nj=Nj(Tx)k,where
Nj(Tx) was converted from Nj(Tx) dBm
into power unit, k= attenuation factor and may be
calculated as
(5)k=C(Tx)C1,where C(Tx)= power injected
into the one segment band at the transmitter side (measured) converted from C(Tx) dBm;  C1= input power at the receiver
device.(iii) By using clearance definition(6)MdB=10log(NNa),
from (3)(7)Na=N−Nj,
and from (4)
(8)Nj=Nj(Tx)k,so,
(9)MdB=10log(NN−Nj(Tx)/k),where k is obtained from (5).The transmitter signal level at the
point B (see Figure4) was fixed at −27 dBm. The
variable Gaussian noise Nj(Tx) injected at the point C (see Figure 4) is
exhibited in the Table 2.Table 2
Field measurement results.
PointN°DistNj(Tx)Average SignalC1Max. SignalClearance*KmdBmdBmdBmdB12−30.91−75.7−73.15.822−30.11−72.5−71.19.632−30.62−77.9−76.16.842−30.33−63.5−61.18.152−30.43−52.5−51.17.662−30.71−71.1−69.16.575−30.57−52.2−51.07.085−30.81−81.3−81.66.195−29.81−73.4−71.013.3105−29.81−65.7−64.013.31110−30.43−88.0−88.07.6With the data collected in the field,
the level clearance was calculated according to the procedure described above.
The clearance value means what is the signal level tolerance, existing in each
site to keep the reception in a good condition. This clearance level depends on
the signal level and the noise level that exist in each point.


## 4.2. Field Measurement Samples

The samples data of measurements
carried out in São Paulo
city for sites located at 2 km, 5 km, and 10 km from the transmitter allows to
calculate the field intensity and the signal level clearance still existing in
each site measured as shown in Table2.
The above distances were selected due to the maximum transmitter power
authorized for test by Brazilian Communications Regulatory Agency was only 1 kW.


## 5. Conclusions

Today, there are many products for
mobile handheld reception available in commerce and this fact opened the possibility
to Mackenzie Presbyterian University
to carry out a field test of these apparatus types by simplified method. The
aim of this work was to develop a simple and reliable field test procedure
allowing to easily executing the outdoor and indoor tests since the unique
instruments necessary to do it are a spectrum analyzer with the attached
receiver and a cellular phone to communicate with the transmitter site.  The field tests were done and they confirmed
the proposed procedures are achievable. The field tests also attested the
reception robustness and quality of the handheld devices used, presenting
promising results for this type of broadcasting.



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*Source: 243937-2008-11-03.xml*