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Digital Radio Mondiale (DRM) Measurement
System Design and Measurement Methodology for
Fixed and Mobile Reception
G. Prieto, D. Guerra, J. M. Mat
´
ıas, M. M. V
´
elez and A. Arrinda
University of the Basque Country – UPV/EHU
Alda. Urquijo S/N, 48013 BILBAO, Spain
{gorka.prieto, david.guerra, josemaria.matias, manuel.velez, amaia.arrinda}@ehu.es
Abstract— This paper presents a measurement system design
and the measurement techniques developed to study DRM (Dig-
ital Radio Mondiale) signal behavior and system performance.
The solution proposed considers different reception conditions
and environments. Some aspects, like antenna selection and both
internal and external noise measurement, have turned to be key
factors and are also presented.
Index Terms— Measurement system, mobile measurements,
external noise, receiver sensitivity, DRM.
I. INTRODUCTION
D
RM (Digital Radio Mondiale) is the standard adopted in
Europe for digital audio broadcasting in the frequency
bands below 30 MHz [1]–[3]. The work of developing all
the technical, promotional and standardization tasks has been
mainly carried out by the members of the DRM consortium
[4]. The result of this collaborative effort is a successful launch
of commercial emissions in June 2003 by the 16 leading
international broadcasters.
Despite this successful launch of services, there is still a
need for network parameter planning values measured on the
field [5], [6], and also to analyze the behavior of the DRM
system under several reception environments and conditions.
In order to perform this measurement campaign as efficiently
and productively as possible, both a measurement mobile unit
and a special measurement methodology have been designed.
DRM allows a number of parameters to be adjusted to
provide a better performance for the different propagation
cases and reception conditions that can occur using these
frequency bands [7], [8]. These parameters range from OFDM
related parameters, such as number of carriers and guard
interval, to symbol and bit-stream related parameters, such
as interleaver depth and protection ratios. The designed mea-
surement methodology takes this into account. It allows to
remotely change the transmitter parameters from the mobile
unit in order to test different signal configurations and also to
perform different kinds of measurements.
Some important conclusions were also obtained while im-
plementing the measurement system and performing the first
tests. Man made noise has a great impact on reception quality
and is a key factor when choosing a suitable antenna for DRM
UPV/EHU is a member of the System Evaluation (TC-SE) and Monitoring
Network (TC-MN) groups of the DRM Consortium.
reception. Noise measurement has turned to be a need, and
suitable equipment configuration and measurement methodol-
ogy has been designed.
II. MEASUREMENT SYSTEM
A. Measurement Targets
The measurement system presented in this document has
been designed with the aim of studying a range as wide as
possible of aspects for this emerging technology, and the low
bandwidth of the DRM signal has contributed to this goal.
Among these aspects, the targeted ones are the following:
• A first aspect to study is the evaluation of suitable channel
propagation models. This evaluation implies obtaining the
time and spatial behavior of the received signal level.
• A second aspect is the characterization of fixed reception
parameters. This characterization includes a minimum
SNR and minimum field strength requirement measure-
ment and its comparison to the initial values obtained
from laboratory simulations and recommended by the
ITU-R [9].
• Another key aspect to study is the characterization for
mobile reception. Relevant measurements in this mobile
reception are the effects of power lines and tunnels
depending on the vehicle speed.
• All these measurements must be done taking into account
different reception environments such as rural, residential
and commercial.
• Finally the system must be able to dynamically modify
the parameters of the transmitted signal to measure their
effect on the reception experience.
B. Measurement System Design
The DRM measurement system that has been designed
is depicted in figure 1. The measurement system allows to
be installed on a van in order to carry out a measurement
campaign with a mobile unit. From figure 1 it can be seen
that the system is composed of three different sections: the
acquisition and distribution section, the measurement section
and the control section.
The acquisition and distribution section is composed of
the Rohde&Schwarz HE010 short monopole active antenna
2
Fig. 1. DRM Measurement System Architecture
with a 40 MHz low-pass filter modification in order to avoid
undesired out of band interferences. The antenna is placed at
the top of the van with a specifically prepared ground plane.
Then the received signal passes though a variable logarithmic
attenuator, and the distribution to the rest of the equipment is
done using two power splitters.
The measurement section is composed of two main blocks.
The first one (the DRM receiving chain) is composed of the
AOR7030 analogue front-end, capable of tuning the received
signal and down-convert it to a 12 kHz intermediate frequency.
The next component in the chain is a SB Extigy external sound
card responsible of sampling the 12 kHz IF signal and sending
the samples to a PC, which is the actual DRM demodulator.
For this purpose the professional version of the FhG software
radio has been used.
The other block of the measurement section is responsible of
measuring the field strength and capturing the RF spectra. It is
composed of a vectorial signal analyzer to provide spectrum
traces and a field strength meter to measure the RF signal
power.
The last section is the control system, responsible of con-
figuration and control of all the equipment, data storage,
online statistics calculation and position measurement. This
section also provides a GUI to a human user. The control
system is based on a laptop running a designed software on a
GNU/Linux platform.
This section includes auxiliary devices such as a GPS
and a tachometer trigger system, which provides a precise
reference to calculate wavelength based statistics for mobile
measurements. The tachometer also provides a backup of the
GPS in case this last one fails, as happens inside tunnels and
places of bad coverage.
In order to allow to change the transmitted signal parameters
from the mobile unit, a remote control system has been
implemented. It is based on a call server located in the
transmitter, ready to receive and answer GSM data calls from
the measurement mobile unit. This process is automated via
UNIX shells scripts which connect the modem to the network
and execute remote commands via SSH. The access to the
GSM network is done via two identical modules located in
the van and in the transmitter.
C. Antenna Selection
Antenna selection has turned to be a key factor in order to
achieve good measurement results for both signal and noise,
specially for urban environments.
Two types of antennas have been considered. A passive
magnetic transfer helical antenna and a R&S HE010 short
monopole active antenna. The active one has two main ad-
vantages: it is characterized by the manufacturer, and has a
wider frequency response. But this wide frequency response
has a big counterpart since FM transmissions up to 100 MHz
are also amplified. This leads to antenna saturation noise in
environments with high signal power out of the DRM band,
such as FM transmissions in urban environments. For these
later cases the passive antenna solves the problem, but this
antenna is not characterized. The solution adopted consists on
using the active antenna but with a 40 MHz limiter before the
feeder, thus filtering non-DRM signals.
Figure 2 shows an AM spectrum measured with the men-
tioned antennas in a noisy urban environment. From this figure,
the antenna saturation noise effect is clear for the original
active antenna. The antenna with the 40 MHz limiter, on
the contrary, does not suffer from this saturation noise and
amplifies both signal and noise above the internal measurement
equipment noise. The passive antenna logically also avoids
3
−10 −8 −6 −4 −2 0 2 4 6 8 10
−120
−110
−100
−90
−80
−70
−60
−50
−40
−30
Frequency (MHz)
Power (dBm)
PASSIVE HELICAL
ACTIVE HE010
ACTIVE HE010
(WITH 40 MHz FILTER)
INTERNAL NOISE FLOOR
Fig. 2. Measured AM spectrum in a noisy urban environment
saturation noise, but gives signal values closer to the mea-
surement equipment internal noise floor.
D. Internal Noise Floor
It is very important to characterize the internal noise floor
of the measurement system in order to determine the smallest
signal level than can be measured with it. If the received signal
level is close to the internal noise floor of the equipment, the
measured level would be distorted.
The two key elements of the presented DRM measurement
system that have to be analyzed are the field strength meter
and the DRM receiver. The procedure that has been used for
measuring the internal noise floor for both equipments consists
on generating a DRM signal to feed the system and vary its
power in 1 dB steps.
The field strength meter is expected to initially provide
measured values in steps of 1 dB, but these steps would
become smaller as the input signal level approaches to the
internal noise floor.
In relation to the DRM receiver, which consists on the
analogue front-end and the sound card, this absolute signal
level value cannot be measured. In this case, the signal to
noise ratio of the samples captured by the sound card is used
instead. This ratio should remain constant until the external
noise level reaches the internal noise floor of the receiver,
starting then to decrease until being zero.
This behavior has been measured and its depicted in figure
3 for both the field strength meter and the DRM receiver.
Since both the DRM signal and the noise signal have the
same distribution (gaussian) and are uncorrelated, the power
level measured by the field strength meter for the resulting
signal is the lineal sum of the power of each of the signals.
Equation (1) shows this sum in logarithmic scale.
P
M
= 10 · log
10
P
R
10
+ 10
N
10
(1)
where
P
M
measured power
P
R
real power
N internal noise floor
−15−10−50510152025303540
−5
0
5
10
15
20
25
30
35
40
Measured value (dBuV|dB)
Input signal level (dBuV)
FIELD STRENGTH
METER (POWER)
DRM RECEIVER
(SNR)
Fig. 3. Effect of internal noise floor
For the case of the DRM receiver, the measured SNR
value is affected by both the internal noise floor and the
external noise level. Applying a similar reasoning to the one
presented for the field strength meter, equation (2) is obtained
for describing the behavior of the measured SNR value in
logarithmic scale.
SNR = 10 · log
10
S
10
+ 10
R
10
+ 10
N
10
(2)
−10 · log
10
R
10
+ 10
N
10
where
SNR measured signal to noise ratio
S signal power
N internal noise floor
R external noise power
The method designed for working out the internal noise
floor values for both the field strength meter and the DRM
receiver consist on applying a MMSE criterion. The obtained
noise values minimice the MSE between the theoretical behav-
ior described by (1) and (2) and the measured values depicted
in figure 3.
The results of applying this procedure are depicted in figures
4 and 5 for the field strength meter and the DRM receiver
respectively. The obtained values are summarized in table I.
These values are referenced to the input of the measurement
system, to reference it to the input of their corresponding
equipments, the attenuation inserted by the distribution system
must be subtracted. This attenuation is 6 dB for the DRM
receiver and 12 dB for the field strength meter.
Field strength DRM
meter receiver
Internal
−5.1 dBµV −4.1 dBµV
noise floor
Noise
22.3 dB 23.3 dB
figure
TABLE I
MEASURED NOISE FLOOR AND NOISE FIGURES
4
−10 −9 −8 −7 −6 −5 −4 −3 −2 −1 0
0
0.5
1
1.5
2
2.5
3
3.5
4
MSE (dBuV)
Internal noise (dBuV)
Fig. 4. MMSE results for the field strength meter
Finally it must be pointed out that, in order to achieve these
small noise values for the case of the field strength meter, it
has been necessary to switch on its internal preamplifier of
20 dB and switch off its input attenuator of 10 dB.
III. MEASUREMENT METHODOLOGY
A. Measurement Parameters
Part of the desired measurement parameters are provided by
the DRM receiver via a standardized interface but, beside these
parameters, additional measurements must be done for RF
analysis and also for logging position and speed information.
The measurement parameters that a DRM professional
receiver should provide are standardized by the RSCI (Re-
ceiver Status and Control Interface) specification [10]. These
parameters can be accessed via DCP (Distribution and Com-
munications Protocol) which is also standardized [11].
RSCI provides a quite wide range of parameters which
include: channel measurements like delay and Doppler spread,
constellation measurements like MER, and baseband measure-
ments like number of errored bits and audio dropout patterns.
All of these parameters are provided every 400 ms, which
is the duration of a DRM frame, and are recorded by the
measurement system.
Due to this time constraint, this 400 ms interval has been
chosen as the base measurement interval for the rest of
the equipment in the system. In addition to all the RSCI
measurements, the DRM signal strength is also measured
integrating the received level during 400 ms (longer than a
symbol duration) using a RMS detector. For the case of fixed
measurements a measurement duration of several minutes is
recommended to take into account the influence of external
agents like traffic passing near the measurement unit.
For the case of mobile measurements a tachometer trigger
has been designed in order to provide a precise reference
to calculate wavelength based measurements. These measure-
ments are recorded every a preconfigured number of turns
of the van wheel, which defaults to a sampling distance of
λ/10. This spacing is considered small enough to study which
could be a recommended spacing value in order to avoid
5
7
9
11
13
15
−10
−8
−6
−4
−2
0
0
5
10
15
20
External noise (dBuV)
Internal noise (dBuV)
MSE (dBuV)
Fig. 5. MMSE results for the DRM receiver
waveform sampling redundancy at these low frequencies.
Studies performned for other frequency ranges have obtained
recommended sampling distances of 0.9λ [12] and 0.38λ [13].
B. SNR Measurement
One parameter of special interest for a broadcasting net-
works planning tool is the minimum requirement in the ratio
between the modulated signal RF power and the external noise
level. This is what is denoted in this section as minimum SNR
requirement.
A common procedure for measuring the minimum SNR
requirement consists on attenuating the input signal of the
system until a threshold BER (Bit Error Rate) is measured
on the receiver. But this is not suitable for all the cases under
study. When the DRM signal uses ground wave propagation
(typical of the medium wave band during daytime), there are
not multipath or Doppler effects that decrease signal quality,
instead the channel behaves as a Gaussian one. Thus the main
cause of decrease on signal quality in this case is a low signal
level or a high external noise level.
From this consideration it is concluded that attenuating the
system input would attenuate both input signal and external
input noise resulting in the same SNR measurement. This
would last until the attenuated input noise is lower than the
measurement equipment internal noise floor, in which moment
the measured SNR begins to decrease. This is shown in figure
6.
This figure shows how SNR, and thus BER, remains con-
stant until the equipment internal noise is reached. This is not
the desired measurement since the minimum SNR requirement
would be measured in relation to the internal noise floor of
the receiver, instead of in relation to the external noise level
of the reception environment.
From this consideration it is concluded that finding locations
with the desired SNR or BER range would be a much better
solution than attenuating the input signal. This would result
on a set of BER versus SNR measurements corresponding to
different locations, and then an interpolation algorithm as the
5
0 5 10 15 20 25 30 35
−20
−15
−10
−5
0
5
10
15
20
25
Input attenuation (dB)
Measured value
S (dBuV)
N (dBuV)
SNR (dB)
BER
Fig. 6. Attenuating system input attenuates both signal and external noise
one described in [14] could be used to obtain a minimum SNR
requirement for a given threshold BER.
C. External Noise Measurement
This measurement system has been designed in such a way
that can be used to make external noise measurements in the
DRM bands.
As explained in section II-C the 40 MHz limiter before the
antenna feeder avoids interference of strong signals out of the
DRM bands. Furthermore, the antenna generated noise [15] is
supposed to be 10 dB below the expected value for external
noise levels [7].
In relation to the internal noise floor of the measurement
system, the results presented in section II-D have been ob-
tained for the medium wave band. These values are small
enough in comparison to external noise levels of the medium
wave band. For the case of other DRM bands, a study similar
to the one presented should be performed to assure good
measurement results.
IV. CONCLUSION
This paper has presented a measurement system design
and a measurement methodology optimized for testing and
characterization of the DRM signal behavior and perfor-
mance. Since this is an emerging technology, carrying out
measurement campaigns is something undoubtedly necessary.
These measurements allow to test the system performance and
provide a guidance for planning values to be recommended.
The system presented in this paper has been of a great help
to achieve these tasks and has been successfully used in the
first two DRM measurement campaigns for the medium wave
band carried out in Spain [16], [17].
It is also important to point out that the antenna and noise
considerations presented in this paper are of crucial importance
in order to achieve quality measurement results.
ACKNOWLEDGMENT
The authors would like to thank to the colleagues within
the DRM consortium for their suggestions and help.
This work has been economically supported by public fund-
ing under the scope of the projects MCYT TIC2002-01340 and
UPV/EHU-UE2003.
REFERENCES
[1] System for digital sound broadcasting in the broadcasting bands below
30 MHz, International Telecommunications Union ITU-R Recommen-
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[8] Propagation factors affecting systems using digital modulation tech-
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[9] Planning parameters for digital sound broadcasting for frequencies
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[10] Digital Radio Mondiale (DRM); Receiver Status and Control Interface
(RSCI), European Telecommunications Standards Institute Std. ETSI TS
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Protocol (DCP), European Telecommunications Standards Institute Std.
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[15] Manual Active Rod Antenna HE010, Rohde&Schwarz, 1997, Order No.
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[16] D. Guerra, G. Prieto, I. Fern
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[17] G. Prieto, M. M. V
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elez, P. Angueira, D. Guerra, D. de la Vega, and
A. Arrinda, “Digital Radio Mondiale (DRM). Field Trials for Minimum
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All Authors are members of the TSR (Signal Processing and Radiocommuni-
cations) Research Group. This group belongs to the Department of Electronics
and Telecommunications at the Bilbao Engineering College (University of the
Basque Country) and focuses its main interest on digital broadcasting systems.
