Grundig Digital Radio User Manual
FOREWORD
The purpose of the Digital Radio Guide is to help engineers and managers in the radio broadcast
community understand various aspects of digital radio systems that are available in 2006. The
guide covers those systems used for transmission in different media, but not in the production
chain. The in-depth technical descriptions of the systems are available from the proponent
organisations and their websites listed in the appendices. The choice of the appropriate system
remains the responsibility of the broadcaster who should take into account the various technical,
commercial and legal factors relevant to the application.
It is my sincere hope that the publication will be a useful tool for radio broadcasters to evaluate
the various options available to them.
I would like to thank the editorial team for the excellent job they did in preparing this revised
edition of the Digital Radio Guide. The team was chaired by Wayne Heads, ABU Technical
Director, and consisted of Franc Kozamernik and David Wood, EBU, and Mike Starling, NABA.
We are grateful to the many organisations and consortia whose systems and services are
featured in the guide for providing the updates for this latest edition. In particular, our thanks go
to the following organisations:
• European Broadcasting Union
• North American Broadcasters Association
• Digital Radio Mondiale
• iBiquity Digital
• WorldDAB Forum
• WorldSpace Inc
Dr Riyadh Najm
Chairman
World Broadcasting Unions - Technical Committee
November 2006
3
TABLE OF CONTENTS
1 INTRODUCTION............................................................................................................................... 7
2 WHAT IS DIGITAL RADIO?........................................................................................................... 8
3 WHY DIGITAL RADIO? ................................................................................................................ 10
4 TERRESTRIAL TRANSMISSION SYSTEMS............................................................................. 11
4.1 DRM – D
IGITAL RADIO MONDIALE ........................................................................................... 11
4.1.1 Key Features of the System Design for the Markets to be Served by the DRM System ........ 11
4.1.2 Brief Description of the DRM System ................................................................................... 12
4.1.3 Transmitter Considerations .................................................................................................. 17
4.1.4 DRM+................................................................................................................................... 18
4.2 DAB – E
UREKA 147................................................................................................................... 19
4.2.1 System Development ............................................................................................................. 19
4.2.2 Principal Advantages and Challenges.................................................................................. 19
4.2.3 DAB Development Worldwide as of 2006............................................................................. 21
4.2.4 Infrastructure Requirements ................................................................................................. 25
4.2.5 Synergies with Other Systems ...............................................................................................25
4.2.6 Future Developments of DAB ............................................................................................... 27
4.2.7 Types of Receivers ................................................................................................................ 31
4.3 J
APAN'S DIGITAL RADIO BROADCASTING (ISDB-TSB) ............................................................. 35
4.3.1 Overview............................................................................................................................... 35
4.3.2 The Methods.......................................................................................................................... 35
4.3.3 Characteristics...................................................................................................................... 41
4.3.4 Receivers............................................................................................................................... 41
4.3.5 Overview of Services............................................................................................................. 42
4.3.6 Outlook for the Future .......................................................................................................... 43
4.4
IBIQUITY HD RADIO SYSTEM..................................................................................................... 44
4.4.1 HD Radio Standards Activity................................................................................................45
4.4.2 HD Radio AM and FM Receivers ......................................................................................... 45
4.4.3 HD Radio System Technical Design Overview..................................................................... 46
4.4.4 Core Services ........................................................................................................................ 47
4.4.5 HD Radio Subsystems........................................................................................................... 50
4.4.6 Receiver Systems................................................................................................................... 52
4.4.7 Features Common to North American Digital Radio Systems.............................................. 53
4.4.8 Infrastructure Requirements ................................................................................................. 56
4.5 I
SSUES RELATED TO TERRESTRIAL SYSTEMS .............................................................................. 58
4.5.1 Spectrum Availability............................................................................................................ 58
4.5.2 The Implications of Simulcasting.......................................................................................... 62
4.5.3 Coverage............................................................................................................................... 63
5 SATELLITE TRANSMISSION ...................................................................................................... 65
5.1 W
ORLDSPACE – ITU-R SYSTEM D............................................................................................. 65
5.1.1 Receiver Systems................................................................................................................... 68
5.2 SIRIUS S
ATELLITE RADIO /XMSATELLITE RADIO................................................................... 69
5.2.1 Sirius Overview..................................................................................................................... 70
5.2.2 Deployment Status ................................................................................................................ 74
5.3 M
OBILE BROADCASTING CORP. AND TU MEDIA CORP. – ITU-R SYSTEM E.............................. 75
5.3.1 Receiver Systems................................................................................................................... 75
6 INTERNET RADIO (IR) ................................................................................................................. 76
6.1 I
6.2 B
NTRODUCTION........................................................................................................................... 76
RINGING RADIO TO THE INTERNET ........................................................................................... 76
5
6.3 INTERNET RADIO PECULIARITIES................................................................................................ 77
6.4 I
6.5 I
6.6 S
6.7 I
6.8 I
6.9 M
6.10 C
NTERNET RADIO AS A COMPLEMENT TO ESTABLISHED RADIO SERVICES ................................... 78
NTERNET-ONLY STATIONS:IRPORTALS AND MUSIC PORTALS ................................................. 79
TREAMING TECHNOLOGY FOR RADIO SERVICES ........................................................................ 79
NTERNET RADIO TERMINALS AND PLAYBACK DEVICES ............................................................. 82
NTERNET RADIO'S RELATION WITH THE TRADITIONAL RADIO ................................................... 83
EASURING AUDIENCE .............................................................................................................. 84
ASE STUDIES ............................................................................................................................ 86
6.10.1 VRT .................................................................................................................................. 86
6.10.2 Virgin Radio..................................................................................................................... 86
6.10.3 Swedish Radio multichannel audio distribution............................................................... 87
6.11 S
6.12 S
UMMARY AND CONCLUSIONS ................................................................................................... 87
OME IMPORTANT RADIO PORTALS ........................................................................................... 88
7 SOME SOURCES FOR THE DIGITAL RADIO GUIDE............................................................ 91
APPENDIX A THE EUREKA 147 SYSTEM - SYSTEM DESCRIPTION.................................. 94
APPENDIX B RELEVANT WORLD WIDE WEBSITES........................................................... 110
APPENDIX C GLOSSARY OF ACRONYMS.............................................................................. 112
6
DIGITAL RADIO GUIDE INTRODUCTION
1 Introduction
Digital technology has steadily transformed the way in which programmes are made and
distributed in recent years. Already many broadcasters have invested in digital systems
for contribution and production and now the switch from analogue to digital is moving
along the broadcasting chain into transmission. At the same time, digital developments
are drawing together the broadcasting, telecommunications and computer industries in a
process of convergence. For all broadcasters, this is leading to a new and challenging
business environment in which they are searching for a clear ‘multimedia’ role.
Although similar changes are happening in both radio and television, this guide deals with
radio. It is designed to help managers, including those in developing countries, identify
the technical and business forces that are driving the analogue to digital conversion
process. There are many benefits that radio broadcasters stand to gain by adopting
digital technology and the current interest in digital television should help and encourage
the switch from analogue to digital in radio broadcasting. The issue is likely to be brought
into sharper focus if and when individual countries or regional groups set timetables for
phasing out existing analogue services.
This updated Digital Radio Guide focuses primarily on the various digital radio systems in
operation today and their associated standards. The guide visits not only terrestrially
based digital system but also overviews the services now available via satellite radio.
The important development seen in this updated guide is the significant changes to
digital radio development compared to the original guide published in 1998. The first
guide presented many options for the US-based studies into digital radio as well as
satellite radio. These systems have now matured to the level that there is unlikely to be
changes in the choice for digital standards for many years. The only development
planned at present is that by the DRM Consortium with its DRM120 project.
This guide is a compilation of inputs provided by WBU members for the benefit of the
world broadcasting community. Note that references to relevant worldwide websites and
a glossary of acronyms are provided in Appendices B and C at the end of this guide.
7
DIGITAL RADIO GUIDE WHAT IS DIGITAL RADIO?
2 What is Digital Radio?
Since the early days of broadcasting, analogue systems have been used to carry
programmes from the studios to the listeners. Now, due to the growing number of
broadcasters and programme services, the frequency bands allocated to AM and FM
radio in many regions of the world are full. The resulting congestion in the radio spectrum
has led to a decline in reception quality and is a real constraint to further growth.
Furthermore, in densely populated areas, FM reception on car radios and portables can
be very poor. This is due to the effect of severe multipath propagation caused by signal
reflections and shadowing due to high buildings.
Digital transmission technology can offer much improved coverage and availability. It is
expected to replace analogue transmissions in many areas, but as digital systems are
incompatible with current AM and FM broadcasting systems, new receivers will be
needed.
In basic form, digital radio is an application of the technology in which sound is processed
and transmitted as a stream of binary digits. The principle of using digital technology for
audio transmission is not new, but early systems used for terrestrial television sound
(such as NICAM 728) need considerable bandwidth and use the RF spectrum inefficiently,
by comparison with today’s digital systems.
The development of digital radio has been helped by the rapid progress that has been
made in digital coding techniques used in RF and audio systems. This has led to
improved spectrum efficiency, more channel capacity, or a combination of these benefits.
Digital compression techniques used in audio systems have improved sound quality at
low bit rates to the extent that radio broadcasts can be made on location and then
transmitted to the broadcaster’s production studios over telephone circuits in high quality.
Ideally, to reach the widest range of listeners, a genuinely universal digital radio system
should be capable of being transmitted via terrestrial, satellite and cable systems.
There are new digital radio systems in operation. The list is set out in Table 2.1.
The table illustrates the wide spread of operational systems throughout the world.
The great strength of the present analogue transmission systems is the world-wide
standardisation on just two systems (FM and AM). This enables listeners to use one radio
to receive programmes at any location. But in the development of digital systems, it is
now clear that similar standardisation will not be so easily achieved. Differing market
requirements are driving digital systems to be more specialised and tailored to meet
regional, national, or application-oriented needs. Furthermore, the complexity of digital
systems compared to existing analogue techniques fosters this differentiation.
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DIGITAL RADIO GUIDE WHAT IS DIGITAL RADIO?
Table 2.1. Digital Radio Systems
AVAILABILITY
SYSTEM Terrestrial in service date Satellite in
service date
Eureka 147
(ITU-R Digital System A)
1995
(for the UK, Norway,
---
Denmark and Sweden)
DRM - Digital Radio Mondiale
ETSI ES 201 980 V1.2.2 (2003-4)
International consortium
Transmissions tests
successfully since 2000;
regular broadcasting from
---
July 2003. For use in all
broadcasting bands below 30
MHz
DRM - Digital Radio Mondiale 2010
DRM+
HD Radio (iBiquity Digital)
Now rolling out in US --(FCC Docket 99-325, NRSC-5
Standard) in the HF and MF Bands
WorldSpace
1998
(ITU-R Digital System D)
XM Radio 2001 (North
America)
Sirius Satellite Radio 2000 (North
America)
Digital Radio Broadcasting
(1) --ISDB-TSB (Japan)
Notes:
--- Not applicable
(1) System under trial development. No date set for a service.
9
DIGITAL RADIO GUIDE WHY DIGITAL RADIO?
3 Why Digital Radio?
The existing AM and FM analogue systems suffer from inherent short-comings and
neither can offer uniform reception quality throughout the coverage area. AM radio
reception is constrained by bandwidth limitations, which restrict the audio quality and by
interference from other co-channel and adjacent channel transmissions. This is
particularly troublesome during the hours of darkness. The start of FM services in the
1950’s improved the audio bandwidth and overcame the night-time interference, but the
broadcasts were designed to be received using fixed receivers with external antennas.
When listened to in vehicles or on portables, reception suffered from the effects of
reflected signals (multipath) and other forms of interference, particularly in suburban and
city areas.
Another aspect of AM and FM analogue transmissions is the inefficient use of the
spectrum (relative to what is possible using digital technology). As pressure on the radio
spectrum rises, this finite resource becomes more scarce. Digital radio is seen by some
administrations as a potential source of income and spectrum, as a way to encourage the
resource to be used more efficiently.
There are many ways in which digital radio systems can improve upon analogue
systems:
• Digital signals are more robust than analogue and can be transmitted successfully at
lower transmitter powers.
• Digital systems using coded multicarrier modulation offer much improved reception
on mobile car radios and portables.
• Advanced digital compression techniques enable low bit rates to be used
successfully, whilst still producing sound of near CD quality. This makes digital
systems more spectrum efficient.
• The digital bit-stream can be used for transmitting both audio and data.
• A digital radio is much easier to use/tune than is an AM/FM radio.
• There is increasing competition for the public’s time from the non-broadcast media
such as the CD. By comparison, many AM (in particular) and FM services offer poor
audio quality.
• The data capability of digital radio can be used directly or, with some modification, for
other related broadcasting activities such as Internet radio.
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DIGITAL RADIO GUIDE TERRESTRIAL TRANSMISSION SYSTEMS - DRM
4 Terrestrial Transmission Systems
This section provides a technical overview of the various digital radio systems available
for terrestrial application: DRM, DAB, ISDB-TSB, and HD Radio. These systems operate
in various frequency bands and offer different attributes and features.
4.1 DRM – Digital Radio Mondiale
The DRM system encompasses a high level of flexibility in its design. These are noted in
this subsection in the signal flow sequence going from the delivery from a program studio
or network control centre to a transmission site and on to reception and decoding in a
receiver.
4.1.1 Key Features of the System Design for the Markets to be Served by the
DRM System
The DRM system is a flexible digital sound broadcasting system for use in the terrestrial
broadcasting bands below 30 MHz.
It is important to recognize that the consumer radio receiver of the near future will need to
be capable of decoding any or all of several terrestrial transmissions; that is narrow-band
digital (for <30 MHz RF), wider band digital (for >30 MHz RF), and analogue for the LF,
MF, HF and VHF (including the FM) bands. In addition there is the possibility of satellite
delivery reception in the L- and S-bands. The DRM system will be an important
component within the receiver. It is unlikely that a consumer radio designed to receive
terrestrial transmissions in the near future with a digital capability would exclude the
analogue capability.
In the consumer radio receiver, the DRM system will provide the capability to receive
digital radio (sound, program related data, other data, and still pictures) in all the
broadcasting bands below 30 MHz. It can function in an independent manner, but, as
stated above, will more likely be part of a more comprehensive receiver – much like the
majority of today’s receivers that include AM and FM analogue reception capability.
The DRM system can be used in either 9 or 10 kHz channels, or multiples of these
channel bandwidths. Differences on how much of the total available bit stream for these
channels is used for audio, for error protection and correction, and for data transfer
depend on the allocated band (LF, MF or HF) and on the intended use (for example,
ground wave, short distance sky wave or long distance sky wave, with a data application
service or without one). In other words, there are modal trade-offs available so that the
system can match the needs of broadcasters worldwide.
As noted in more detail in subsequent parts of this subsection, the DRM system has the
following structure. It employs advanced audio coding (AAC), supplemented by spectral
band replication (SBR), as the main digital audio encoding. These are parts of the
MPEG-4 audio standard. SBR significantly improves perceived audio quality so that the
overall audio quality of a DRM signal is similar to that of FM (mono). Orthogonal
Frequency Division Multiplexing (OFDM) and Quadrature Amplitude Modulation (QAM)
are used for the channel coding and modulation, along with time interleaving and forward
error correction (FEC). Pilot reference symbols are injected to permit a receiver to
“equalize” the channel by comparing a known stored bit sequence with the corresponding
received sequence of these special bits, and adjusting accordingly if there are differences
in the received compared to the stored sequence.
11
DIGITAL RADIO GUIDE TERRESTRIAL TRANSMISSION SYSTEMS - DRM
r
The combination of these techniques results in high quality sound in a narrow channel
with robust reception in an intended coverage area with relatively low transmission power.
In addition, source coding schemes using lower bit rates than that used with AAC/SBR
are included for lesser levels of audio quality if the AAC/SBR quality level is not desired
by a broadcaster. For example, a broadcaster may want to transmit two or more “speech”
only programs. These would not require the full performance of AAC/SBR.
4.1.2 Brief Description of the DRM System
(1) Overall design
Figure 4.1: Transmission Block Diagram
audio data
stream
stream
information
SDC
information
data
FAC
source
encoder(s)
pre-coder
pre-coder
pre-coder
normal prot.
[high prot.]
normal prot.
[high prot.]
MUX
normal/[high]
protection
energy
dispersal
energy
dispersal
energy
dispersal
flow of information
channel
encoder
channel
encoder
channel
encoder
cell
interleaver
pilot generator
MSC
FAC
SDC
OFDM signal
generator
OFDM cell mappe
Figure 4.1 depicts the general flow of different classes of information (audio, data,
etc.) after their origination in a studio or control centre (that would be depicted to
the left of the figure) to a DRM transmitter exciter/modulator on the right. Although
a receiver diagram is not included in the figure, it would represent the inverse of
this diagram.
There are two classes of basic information:
modulator
DRM transmission signal
• the encoded audio and data that are combined in the main service multiplexer;
• information that bypasses the multiplexer that are known as fast access
channel (FAC) and service description channel (SDC), whose purposes relate
to identification and control for a transmitter and for appropriate decoding
selection within a receiver.
The audio source encoder and the data pre-coders ensure the adaptation of the
input streams onto an appropriate digital format. Their output may comprise two
parts requiring two levels of protection within the subsequent channel encoder.
The multiplex combines the protection levels of all data and audio services in a
proper format within the frame structure of the bit stream.
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DIGITAL RADIO GUIDE TERRESTRIAL TRANSMISSION SYSTEMS - DRM
The energy dispersal provides an ordering of the bits that reduces the possibility of
unwanted regularity in the transmitted signal.
The channel encoder adds redundant bits as a means for error protection and
correction and defines the mapping of the digitally encoded information into QAM
cells, which are the basic carriers of the information supplied to the transmitter for
modulation.
Cell interleaving rearranges the time sequence of the bits as a means of
“scrambling” the signal so that the final reconstruction of the signal at a receiver will
be less affected by fast fading than would be the case if “continuous” speech or
music were transmitted.
The pilot generator injects information that permits a receiver to derive channelequalization information, thereby allowing for coherent (includes phase information)
demodulation of the signal.
The OFDM cell mapper collects the different classes of cells and places them on a
time-frequency grid.
OFDM depends on each of many subcarriers carrying its own sinusoidal
amplitude/phase signal for a short period of time. The ensemble of the information
on these subcarriers contains what is needed for transmission. In the case of DRM,
for a 10 kHz channel, there are hundreds of subcarriers.
The modulator converts the digital representation of the OFDM signal into the
analogue signal that will be transmitted via a transmitter/antenna over the air –
essentially phase/amplitude representations as noted above modulating the RF.
With a non-linear high-powered transmitter, the signal is first split into its amplitude
and phase components for injection in the anode and grid circuits, respectively,
and then recombined (by the action of the transmitter itself set at the correct
differential delay time), and then recombined prior to final emission. This splitting is
not necessary for linear amplification.
(2) Distribution Interface
Referring to the extreme left of Figure 4.1, apart from audio and data applications
that are multiplexed, additional information is sent that is required to instruct the
transmitter to select the correct mode, error protection level, etc. and to send
information in the transmission to the receivers to permit them to switch to the
selection of several variables to allow for proper decoding. (The boxes and arrows
for this are not shown directly in Figure 4.1.) In the aggregate, this collection of
information and the means to get it to the transmitting station is called the
“Distribution Interface” (DI).
These signals can emanate from a studio, or from a more elaborate network
control centre, and be transmitted via land lines or via satellite circuits to the
appropriate transmitter station(s). These details will not be noted here, but can be
found in ETSI documents TS 102 821 and TS 102 820, both dated July 2003.
In terms of connections with other parts of the DRM system, these signals, as
appropriate, are placed in either the Fast Access Channel (FAC) or the Service
Description Channel (SDC) for transmission to receivers.
There are 4 categories of data associated with the Distribution Interface:
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DIGITAL RADIO GUIDE TERRESTRIAL TRANSMISSION SYSTEMS - DRM
• MDI – Multiplex Distribution Interface: covers the transport of data and
commands from the DRM multiplexer to the DRM Modulator.
• MCI – Modulator Control Interface: covers the remote signalling of commands
and setups to the modulator and transmitter equipment.
• SDI – Service Distribution Interface: covers the transport of data and
commands from the studio and other sources to the DRM Multiplexer.
• RSCI – Receiver Status and Control Interface: covers the transport of receiver
status information in addition to the DRM multiplex as well as commands to
control the receiver’s behaviour.
(3) Audio Source Coding
Figure 4.2 depicts the variety of digital audio encoders in the DRM system – in
effect, AAC, AAC with SBR, CELP and HVXC – all of which can operate in a range
of bit rates, and consequently produce a range of audio quality. (See the ETSI
DRM standardization document ES 201 980 v2.1.1, 2004-06.)
The full range runs approximately from 2 kbps (HVXC minimum) to 25 kbps (AAC
maximum) within the 9/10 kHz channels for standard broadcasting in the
broadcasting bands below 30 MHz. HVXC and CELP are used for “speech only”
applications. AAC and AAC/SBR, within the permissible range, result in excellent
music and speech audio quality.
Audio signal
Figure 4.2: DRM Source Encoding and Decoding
DRM Source Encoding
AAC
Encoder
SBR Encoder
(configuration
dependent)
CELP
Encoder
HVXC
Encoder
Audio
super
framing
mux &
channel
coding
14
DIGITAL RADIO GUIDE TERRESTRIAL TRANSMISSION SYSTEMS - DRM
DRM Source Decoding
AAC
Decoder
bit
stream
super
framing
demux
CELP
Decoder
HVXC
Decoder
SBR
Decoder
Extensive tests on these codecs at the sampling rates and resulting “bandwidths”
have determined that AAC and especially AAC with SBR produce a perceived
audio quality to listeners that is effectively the equivalent of monophonic FM in a 9
or 10 kHz channel. HVXC produces intelligible speech quality with bit rates of 2 to
4 kbps for HVXC and CELP produces excellent speech quality using around 8 kbps.
All of these codecs are a part of the MPEG-4 audio standard.
SBR (Spectral Band Replication) is a special means of enhancing the perception of
a spectrally truncated low band audio signal by utilizing, on a dynamic basis, the
spectral content of the low band information to simulate the missing higher band
behaviour. This requires about 2 kbps and therefore does not seriously subtract
from a 20 to 25 kbps AAC output.
In concept, the technique is not complicated. Consider a violin as an example. A
string stimulated by a bow and the placement of a finger on the string produces a
fundamental frequency and harmonics characteristic of a violin. These frequencies
can go as high as the audibility of the human ear – say somewhere between 15
and 20 kHz.
Audio
output
For a 9 or 10 kHz channel, the AAC sampling and processing of the violin’s output
can only cover the lower part of the audio spectrum, for example not higher than 6
kHz. The SBR algorithm examines this lower band spectrum on a dynamic basis
and infers what the “missing” higher audio frequency “harmonics” probably are.
The level of re-inserted harmonics depends on the 2 kbps SBR helper signal which
describes the shape of the spectral energy in the original signal before truncation
for AAC coding stereo (which uses an additional 2 kbps of SBR). From the
standpoint of a listener, the combined audio output sounds like 15 kHz audio rather
than 6 kHz audio.
(4) Multiplexing, including special channels and energy dispersal
This section refers to the left side of Figure 4.1 through “energy dispersal”, not
including the DI and audio/data encoding portions.
As noted in Figure 4.1, the DRM system total multiplex consists of 3 channels: the
MSC, the FAC and the SDC. The MSC contains the services – audio and data. The
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DIGITAL RADIO GUIDE TERRESTRIAL TRANSMISSION SYSTEMS - DRM
FAC provides information on the signal bandwidth and other such parameters, and
is also used to allow service selection information for fast scanning. The SDC gives
information to a receiver on how to decode the MSC, how to find alternative
sources of the same data, and gives attributes to the services within the multiplex.
The MSC multiplex may contain up to 4 services, any one of which can be audio or
data. The gross bit rate of the MSC is dependent on the channel bandwidth and
transmission mode being used. In all cases, it is divided into 400 millisecond
frames.
The FAC’s structure is also built within a 400 millisecond frame, and is designed
without interleaving, for example, to ensure rapid delivery of the information it
contains. The design without interleaving is also to ensure fastest decoding of
basic data by the Rx before it can do the audio decoding. The channel parameters
are included in every FAC frame segment. The service parameters are carried in
successive frames, one service per frame. The names of the FAC channel
parameters are: base/enhancement flag, identity, spectrum occupancy, interleaver
depth flag, modulation mode, number of services, reconfiguration index, and
reserved for future use. These use a total of 20 bits. The service parameters within
the FAC are: service identifier, short identifier, conditional access, language,
audio/data flag, and reserved for future use. These use a total of 44 bits.
The SDC’s frame periodicity is 1200 milliseconds. The fields of information are:
multiplex description, label, conditional access, frequency information, frequency
schedule information, application information, announcement support and
switching, coverage region identification, time and date information, audio
information, FAC copy information, and linkage data. As well as conveying these
data, the fact that the SDC is inserted periodically into the waveform is exploited to
enable seamless switching between alternative frequencies.
(5) Channel coding and modulation
The coding/modulation scheme used is a variety of coded orthogonal frequency
division multiplexing (COFDM), which combines the OFDM with the Multi-Level
Coding (MLC) based upon convolutional coding. The convolutional coding provides
a level of error protection. These two main components are supplemented by time
interleaving (“scrambling” of the bit stream) and the provision of pilot
(predetermined value) cells for instantaneous channel estimation. All of this
mitigates the effects of short-term signal fading, whether selective or flat.
Taken together, this combination provides excellent transmission and signal
protection possibilities in the narrow 9 or 10 kHz channels in the LF, MF and HF
broadcasting frequency bands. It can also be used for “multi-channel” DRM use;
that is 18 or 20 kHz channels, using 2 contiguous ITU-R channels. This level of
bandwidth will permit good stereo broadcasting.
For OFDM, the transmitted signal is composed of a succession of symbols, each
including a “guard interval,” which is a cyclic time prefix that provides a “dead time”
to counter intersymbol interference due to multipath delay spread. Orthogonality
refers to the fact that, in the case of the design of the DRM system, each symbol
contains around between 100 and 200 subcarriers spaced evenly across the 9 or
10 kHz channel in such a way that their signals do not interfere with each other
(are orthogonal). The precise number of subcarriers, and other parameter
considerations, are a function of the actual letter modes used: ground wave, sky
wave, and highly robust transmissions.
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DIGITAL RADIO GUIDE TERRESTRIAL TRANSMISSION SYSTEMS - DRM
QAM is used for the modulation that is impressed upon the subcarriers to convey
the information. Two primary QAM constellations are used: 64-QAM and 16-QAM.
The former provides the highest audio quality, but is less robust than the latter. In
addition, a 4-QAM (QPSK) signal, which is very robust, is used for some of the
signalling (but not for the MSC).
The interleaver time span (applied to the MSC) for HF transmission is around 2.4
seconds to cope with time and frequency selective fading by protecting the audio
and data from rapid fades during the natural sequence of speech and music.
Owing to the less difficult propagation conditions for the LF and MF bands, a
shorter interleaver of around 0.8 seconds can be used.
The multi-level convolutional coding scheme uses code rates in the range between
0.5 and 0.8, with the lower rate being associated with the difficult HF propagation
conditions. A 0.5 code rate means that only half the transmitted bits within the
overall coded block are used for the actual services in the multiplex, whereas a 0.8
rate means 80% are.
4.1.3 Transmitter Considerations
Beyond the modulator box in Figure 4.1 is the transmitter exciter. The DRM system
exciter can be used to impress signals on either linear or non-linear transmitters. It is
expected that high-powered non-linear transmitters will be the more usual way of
transmitting, much as is done now with analogue modulation. However, there are
broadcasting service situations where very low powered linear transmissions could be the
best way to serve the public.
With respect to non-linear amplification (Class C operation), the incoming DRM signal
needs to be split into its amplitude and phase components prior to final amplification.
Using QAM modulation, there is a small discrete set of possible amplitudes and phases.
The amplitude component is passed via the anode circuitry; the phase component is
passed through the grid circuitry. These are then combined with the appropriate time
synchronization to form the output of the transmitter.
Measurements of the output spectra show the following: the energy of the digital signal is
more or less evenly spread across the 9 or 10 kHz channel, the shoulders are steep at
the channel edges, and drop rapidly to 40 dB or so below the spectral density level within
the assigned channel, and the power spectral density levels continue to decrease beyond
the 4.5 or 5 kHz from the central frequency of the assigned channel with a rapidity that
permits conformance to the ITU-R mask for the use of the channels.
(1) Over the air
The digital phase/amplitude information on the RF signal is corrupted to different
degrees as the RF signal propagates. Some of the HF channels provide
challenging situations of fairly rapid flat fading, multipath interference that produces
frequency-selective fading within a channel and large path delay spreads of a few
milliseconds or more, and ionospherically induced high levels of Doppler spreads
on the order of 1 or more hertz.
The error protection and error correction incorporated in the DRM system design
mitigates these effects to a great degree. This permits the receiver to accurately
decode the transmitted signal information.
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DIGITAL RADIO GUIDE TERRESTRIAL TRANSMISSION SYSTEMS - DRM
Extensive field tests have verified these performance statements.
(2) Selecting, demodulating and decoding of a DRM system signal at a receiver
A receiver must be able to detect which particular DRM system mode is being
transmitted to handle it properly. This is done by way of the use of many of the
field entries within the FAC and SDC.
Once the appropriate mode is identified (and is repeatedly verified), the
demodulation process is the inverse of that shown in Figure 4.1. Similarly, the
receiver is also informed which services are present, and, for example, how source
decoding of an audio service should be performed.
For much more detail on DRM system, refer to the following references
• ETSI ES 201 980 v 2.1.1 (2004-06): the “signal in the air” specification
• ETSI TS 101 968 v0.0.2 (2002-08): the data applications specification
4.1.4 DRM+
While DRM currently covers the broadcasting bands below 30 MHz, the DRM consortium
voted in March 2005 to begin the process of extending the system to the broadcasting
bands up to 120 MHz. DRM Plus will be the name of this technology and wider bandwidth
channels will be used, which will allow radio stations to use higher bit rate, thus providing
higher audio quality. One of the new channel bandwidths that is likely to be specified is
50 kHz, which will allow DRM+ to carry radio stations at near CD-quality. The design,
development and testing phases of DRM’s extension, which are being conducted by the
DRM consortium are expected to be completed by 2007-2009. A 100 kHz DRM+
channel has sufficient capacity to carry one mobile TV channel: it would be feasible to
distribute mobile TV too over DRM+ than via either DAB or DVB-H.
• ETSI TS 102 820 and TS 102 821: the distribution interface specifications
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DIGITAL RADIO GUIDE TERRESTRIAL TRANSMISSION SYSTEMS - DAB
4.2 DAB – Eureka 147
Eureka 1471 is a digital radio system developed in Europe for reception by mobile,
portable and fixed receivers with a simple non directional antenna. It can be used in
terrestrial, satellite, hybrid (satellite with complementary terrestrial), and cable broadcast
networks and has been designed to operate at any frequency from 30 to 3000 MHz. In
practice, Eureka 147 is being implemented in two spectrum bands, VHF Band III and L
Band. Further details of Eureka 147 can be found in Appendix A: The Eureka 147
System Description.
4.2.1 System Development
Eureka2 was established in 1985 by 17 countries and the European Union to encourage
a bottom up approach to technological development and to strengthen the competitive
position of European companies on the world market. It supports the competitiveness of
European companies through international collaboration, in creating links and networks of
innovation. The 147th Eureka technical project was to develop a digital radio system,
hence Eureka 147.
The Eureka 147 Consortium
France, The Netherlands and the UK. The Eureka 147 standard was defined in 1993 with
ITU Recommendations released in 1994 and an initial ETSI standard released in 1995.
Eureka closed the Eureka 147 project on 1 January 2000.
3
was founded in 1987 with 16 partners from Germany,
The first Eureka 147 prototype equipment was demonstrated in 1988 on the occasion of
the Second Session of WARC-ORB conference held in Geneva. The first consumer type
Eureka 147 receivers developed for pilot projects were released in 1995. The first Eureka
147 services commenced transmitting in the UK, Denmark and Sweden in 1995. Eureka
147 was officially launched at the Berlin IFA (a major consumer electronics show) in 1997.
The WorldDAB Forum
4
was formed in 1995 to encourage international cooperation and
coordination for the introduction of Eureka 147 onto the consumer market. The technical
work previously carried out by Eureka 147 now takes place within the Technical and
Commercial Committee of the WorldDAB Forum. In August 2003, DRM and WorldDAB
announced they would collaborate in the development of their systems.
4.2.2 Principal Advantages and Challenges
Advantages
Eureka 147 is a mature technology that has been implemented in the UK, Germany and
Canada and extensively tested in other parts of Europe and in other countries including
Australia.
Eureka 147 is defined by international ITU recommendations, European ETSI, Cenelec
and IEC standards and national standards (e.g., British receiver standards).
1
Eureka 147 is also known as DAB, Eureka DAB, S!147 (S! is the logo for Eureka projects) and ITU System A. T-DAB
and S-DAB may also be used to distinguish between terrestrial and satellite versions of Eureka 147.
2
Further information on Eureka at www.eureka.be
3
Further information on Eureka-147 consortium at
http://www.eureka.be/ifs/files/ifs/jsp-bin/eureka/ifs/jsps/projectForm.jsp?enumber=147
4
Further information on WorldDAB forum at http://www.worlddab.org/dab
.
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DIGITAL RADIO GUIDE TERRESTRIAL TRANSMISSION SYSTEMS - DAB
Many ancillary aspects of the Eureka 147 system, such as multimedia delivery,
distribution interfaces and user interactivity are also formally defined in ETSI standards.
Eureka 147 can be implemented for a range of applications such as wide area or local
delivery of audio and data services for mobile, portable and fixed reception. It can be
delivered terrestrially, via satellite, cable or a mixture of terrestrial and satellite.
Eureka 147 is designed to be used across a wide spectrum range, from 30 to 3000 MHz,
but has only been implemented using VHF Band III and the 1452 to 1492 MHz segment
of the L Band.
Eureka 147 uses a wideband COFDM modulation system which provides a robust
transmission which is multi path resilient and can provide high availability coverage.
Eureka 147 can be implemented using on channel repeaters in SFNs or low power gap
fillers and extenders. SFNs may also provide “network gain” giving improved service
availability over single channel services.
Eureka 147 can accommodate a varying number of audio services of differing quality with
associated data. The audio quality can range from simple mono speech to CD quality. An
increase in quality requires higher data rates for each audio service, hence reducing the
number of services that can be delivered. Data can also be delivered independently of
the audio services.
Eureka 147 uses mature technologies such as MPEG 1 Layer II and MPEG 2 Layer II
audio coding systems and COFDM modulation, which are also used in the DVB T video
broadcasting standard. This should lead to cheap single chip solutions for receivers.
Eureka 147 has been extensively standardised by European standards organisations and
it would be fairly straightforward for these standards to be adopted as Australia standards
by Standards Australia.
A growing number of Eureka 147 receivers are now available for portable, PCs, mobiles,
in car and in house reception.
Challenges
The MPEG 1 Layer II and MPEG 2 Layer II audio coding systems are now somewhat
dated (compared with new systems) but they offer excellent robustness against channel
errors due to unequal error protection (UEP). The system allows for inclusion of newer
coding systems as independent data, but DAB receivers would need to be adapted or
replaced to receive these services.
While a wide range of DAB receivers is already available on the market, they are still
generally seen as being too costly for general public acceptance, particularly when
compared to the very cheap AM and FM radios that many listeners currently use.
However, as Eureka 147 services have expanded, the cost of receivers have
considerably dropped in price.
Eureka 147 requires services to be multiplexed together before transmission. All audio
programs and data services in a given Eureka 147 channel will therefore have similar
coverage and reception quality.
The standard capacity of Eureka 147 multiplexes means that conversion would require
existing services to be grouped into blocks of 6 or more services per multiplex, all of
which would then cover the same area. In a conversion model, this would pose
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DIGITAL RADIO GUIDE TERRESTRIAL TRANSMISSION SYSTEMS - DAB
challenges for many current radio broadcasting markets, which are typically served by a
mixture of narrowcasting, community, commercial and national services using AM and
FM frequencies with different or overlapping licence and coverage areas giving local,
medium or wide area coverage. Conversely, the requirement for multiplexing could over
time reduce the number of transmission sites and result in more consistent coverage of
services.
Eureka 147 uses spectrum that is often used for analogue and digital television services
(VHF Band III), and radio communication services (L Band). If a conversion model is
used for the introduction of digital radio finding, sufficient spectrum for the conversion of
all analogue radio broadcasting services to digital will not be easy, particularly as L Band
will require more transmitters to provide wide area coverage and adequate reception in
urban areas.
4.2.3 DAB Development Worldwide as of 2006
More than 40 countries have legislated for the integration of DAB Digital Radio in Europe
and Worldwide. Outside Europe the key areas of development are found in Canada, the
Asia-Pacific Region and South Africa.
(1) Belgium
DAB Digital Radio launched in Belgium in September 1997 with a multiplex
operated by the Flemish public broadcaster VRT. Today, the VRT multiplex covers
the Flemish Community and has nine audio stations. Four of these channels are
unique to DAB Digital Radio. RTBF, the public broadcaster for the French
community, has a multiplex covering the French community with five audio stations,
all simulcasts of existing analogue stations.
(2) Canada
DAB launched in Canada in November 1999. Stations in Toronto, Montreal and
Vancouver started operating in 1999; Ontario in 2000; and Ottawa in 2003. There
are currently a total of 73 licensed Digital Audio Broadcast DAB stations in Canada:
15 stations in Ottawa, 25 in Toronto, 15 in Vancouver, 12 in Montreal and 6 in
Windsor. The stations operating in these five cities provide services to some 11
million potential listeners or more than 35% of the population. Seven DAB stations
(4 commercial and 3 public) are field testing in Halifax, Nova Scotia.
DAB has yet to be embraced by consumers in Canada. The industry is currently
evaluating next steps with respect to digital radio rollout. Implementation of other
digital radio systems is under consideration, particularly as rollout of HD Radio in
the neighbouring United States proceeds.
(3) Denmark
Danish Broadcasting Corporation (DR) is currently broadcasting 18 DAB
“channels.” On September 1, 2005, the commercial broadcasters Sky Radio and
Radio 100 FM (owned by Talpa Radio International) commenced transmission on
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DIGITAL RADIO GUIDE TERRESTRIAL TRANSMISSION SYSTEMS - DAB
the DAB networks. Both started simulcasting their FM stations utilising 25 percent
respectively on the national and the two regional networks. DR continues
broadcasting in the remaining 75 percent of both networks.
(4) France
Public broadcaster, Radio France, serves an area covering Paris, Marseille,
Toulouse and Nantes, broadcasting six stations in each of its service areas.
(5) Germany
Germany is among the leading European proponents of DAB Digital Radio with a
large local and regional network. Current figures put coverage in Germany at 78
per cent of the population, rising to 85 per cent by the end of 2005. Germany is the
primary DAB digital radio country in mainland Europe boasting some 120 radio
stations, both public and commercial, on a variety of state-wide as well as local
digital multiplexes. As far as data services are concerned, Germany is at the fore.
The focus lies on news and traffic information, using text and pictures. In March
2005, BLM, the Bavarian Media Authority, launched a pilot project called Digital
Advanced Broadcasting that will aim to use DAB to broadcast radio and video
content, as well as data services, to new portable receives. The pilot will take
place in Regensburg and is expected to last for two years with the aim to work
towards comprehensive coverage of FIFA World Cup 2006 via mobile
entertainment devices.
(6) Italy
Current population coverage in Italy stands at approximately 45% for commercial
operators and 20% for national public operators. There is a scarcity of Band III
spectrum and its use and management for digital and /or analogue TV is yet to be
fully solved. This has caused delay in the roll-out of DAB in Italy.
Italy has been broadcasting DAB Digital Radio since 1995 when public broadcaster
RAI began simulcasting its existing services. In 1998, eight commercial analogue
operators formed a consortium called Club DAB Italia in order to simulcast their
own stations on their own digital multiplex.
Currently nine national commercial stations are broadcast by the Club DAB Italia
consortium in the Milan area and vast adjacent areas and in Rome and adjacent
areas, for about 30 percent of population coverage. Also, five national public
services are simulcast on a multiplex reaching less than 20 per cent population
coverage.
(7) Singapore
Regular DAB Digital Radio services in Singapore were launched on 19th
November 1999. The MediaCorp Radio Singapore Pte Ltd dubbed their multiplex
SmartRadio. SmartRadio carries 14 radio services - six of which are available
exclusively on DAB radio and eight are simulcasts of the more popular FM stations.
In April 2005, Rediffusion, which is Singapore’s sole subscription radio broadcaster,
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DIGITAL RADIO GUIDE TERRESTRIAL TRANSMISSION SYSTEMS - DAB
was awarded a license to provide the world’s first DAB subscription services and
operate its own multiplex.
(8) South Korea
In 2002, the Ministry of Information and Communication (MIC) in Korea approved
the use of DAB for the transmission of audio, video and data using Digital
Multimedia Broadcasting (DMB). In March 2005, six service providers were
selected by the Korean Broadcasting Commission (KBC) to receive licences: KBS,
MBC, SBS, YTN DMB, K-DMB and KMMB. The six broadcasters will in total carry
6 video, 18 audio and 12-18 data programmes, and all will be free of charge at first
to make the service universally available.
(9) Spain
Spain enjoys a strong commitment to DAB Digital Radio, with the current 52 per
cent population coverage expected to rise to 80 per cent by 2006.
DAB Digital Radio in Spain began with pilot stations in 1998 and today is a mix of
public and commercial broadcasting, with 18 stations transmitting digitally.
Spanish broadcasters are currently experimenting with data services and there are
plans for local DAB Digital Radio stations.
(10) Sweden
Whilst there is no coverage requirement built into the digital radio legislation in
Sweden, Swedish Radio, the public broadcaster, covers 85 per cent of the
population. Since 2002, a temporary reduction of the transmissions to 37 per cent
population coverage has been made for financial reasons.
(11) Switzerland
Switzerland currently has approximately 4 million potential listeners (60% of Swiss
population). In 2006, the coverage area in the German speaking part of
Switzerland will be enlarged and indoor reception enhanced. Also, full DAB
coverage across Switzerland has been approved for 2007-2008.
(12) Taiwan
In June 2005 the Taiwan Government awarded 6 commercial multiplex licenses: 3
nation-wide SFN licenses and 3 regional licenses (covering the major conurbations
like Taipei and Causing).
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DIGITAL RADIO GUIDE TERRESTRIAL TRANSMISSION SYSTEMS - DAB
(13) United Kingdom
The public service broadcaster, the BBC, has been promoting its DAB Digital Radio
stations since September 1995 and at present covers over 85 per cent of the
population and includes the major motorway network. Digital One, the UK’s only
national commercial operator, runs the world's biggest digital radio network, with
more than 90 transmitters. Further transmitters are planned to expand the network
towards 90 per cent coverage.
Mid- 2005 saw nearly 150 DAB digital radio products in the market with today’s
figures far in excess of this. The range of DAB radios includes portables, handhelds, boom boxes, clock radios, micro systems, home cinema and in-car products.
Established manufacturers have helped to drive sales with high profile
advertisements in the national press.
The BBC has run a number of campaigns on television, radio and online promoting
DAB digital radio and programme content. Each campaign has seen a surge in
sales of products and consumer awareness rising. During 2005, the BBC
continued to promote individual services and content.
The Digital Radio Development Bureau (DRDB) is funded and supported by UK
broadcasters including the BBC, Digital One, EMAP Digital Radio, MXR and GCap
media. The DRDB's task is to ensure DAB's wide accessibility and swift adoption
in the UK.
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DIGITAL RADIO GUIDE TERRESTRIAL TRANSMISSION SYSTEMS - DAB
Table 4.1. Eureka 147 Main System Features
EUREKA 147
Main System Features
Single Frequency Network (SFN)
capability
All transmitters working on a single
frequency.
Flexible audio bit rate Allows reconfiguration of the multiplex.
Data services Separately defined streams or packets.
Programme Associated Data (PAD) Embedded in the audio bit stream and
adjustable.
Facilitates Conditional Access DAB ensemble transports conditional
access information (CAI) and provides
signal scrambling mechanism.
Service Information Used in the operation and control of
receivers.
Operating frequency range 30 MHz to 3 GHz.
4.2.4 Infrastructure Requirements
Eureka 147 is a wideband technology requiring services to be multiplexed before
transmission. The use of VHF and UHF bands means Eureka 147 services will be
typically transmitted from high sites such as the tops of hills, buildings or towers.
In general, new Eureka 147 services are also likely to be co-located with existing FM
radio or television transmission services given the cost of developing new sites and the
increasing difficulty in getting local council planning approval for new transmission sites.
In Canada, implementation of the Eureka system uses a new band (L-Band), hence new
transmitters, antenna system, exciter and encoders have been required. Stations that
were originally broadcasting more than one FM program from the same site can fully
encapsulate the multiplexed stream of the DAB system in the STL (studio-to-transmitter
link), significantly reducing the costs associated with discrete feeder links. Canada’s
DAB allotment plan has room for the replacement of all existing AM and FM stations in
the L-Band. The plan also includes many empty allotments for future services. Finally,
since the plan was based on providing only five programming channels in each DAB
multiplex, new audio coding schemes will allow for the possible implementation of two to
three additional services in each ensemble.
4.2.5 Synergies with Other Systems
(1) DAB and GSM (Global System for Mobile Communications)
DAB is an efficient broadcasting (e.g., one-to-many) system capable of providing
reliably digital services to all users located in a coverage zone in real time. It is
especially suitable for the reception to mobile and portable receivers and in the
areas in which the direct line of sight between the transmitter and the receiver is
not possible.
On the other hand, GSM (Global System for Mobile Communications) and its
successors (GPRS and UMTS) are more suitable to deliver on-demand media
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DIGITAL RADIO GUIDE TERRESTRIAL TRANSMISSION SYSTEMS - DAB
services to individual clients or relatively small groups of clients. The telecom
systems are technically able to provide services to several users in the same time,
providing that the number of simultaneous users (or, in other words, the total
bandwidth capacity) does not exceed a certain level, or else the network collapses
rapidly. Also, the use of telecom services in the "one-to-many" scenario is much
more expensive for the user than the use of DAB (or DVB) broadcast systems.
It may be advantageous for both broadcasters and telecoms to provide a
combination of both one-to-many and one-to-one applications concurrently. For
example, a traffic/travel information service may consist of two parts: a basic part
and a value-added part. The former would be carried over the broadcast network to
everybody (possibly for free), whereas the latter would be available on-demand
over the telecom network and would be paid-up according to a tariff agreed.
As an example of such synergy, Nagra-Futuris has created an IT infrastructure for
hosting end-to-end interactive services based on the existing GSM and DAB
technologies. The system provides back-channel communication, conditional
access, data warehousing, integrated billing/clearing and interfacing to external Mcommerce providers. The system allows for deployment of interactive services and
dynamic insertion of programme related data. The mobile terminal device is a
combination of mobile phone and DAB receiver. It contains a DAB Identification
Module (DIM).
The EBU have identified many attractive interactive applications and business
opportunities based on DAB/GSM synergy. Such synergetic services may help
telecoms to generate more traffic and offer new, rich-content services (games, live
and on-demand video/audio clips, etc.).
Synergies of GSM and DAB networks may be useful in the case of DAB singlefrequency networks (SFN) at L-Band. To set up an SFN network at L-Band, the
transmission sites must not be any further than 18 km apart using Transmission
Mode II in order to maintain network timing and to benefit from the network gain of
an SFN. Therefore an ideal SFN at L-Band could emulate the infrastructure of
mobile phone networks with lower masts and powers.
(2) Synergies with Digital Radio Mondiale (DRM)
DAB and DRM are complementary as they target different markets. DAB is mainly
intended for local, regional and national audiences. DRM is designed to be
deployed in the frequency bands below 30 MHz to replace existing AM services
and targets more large coverage zones. This system has been successfully
standardised within ITU and ETSI and is now being implemented in the commercial
market. Future listeners will be interested in all services provided by digital radio,
hence radio sets should enable the users to receive any digital radio service
without concern for the transmission system. In terms of the technologies used,
both systems are not too dissimilar; for example, both are using COFDM and
similar channel coding strategies. To this end, common integrated circuits are
being developed and integrated DAB/DRM receivers could soon appear in the
market. A common interface for external devices is also being developed.
In August 2003, DRM and WorldDAB announced they would collaborate in the
development of their systems." Reference: http://www.worlddab.org/press.aspx
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DIGITAL RADIO GUIDE TERRESTRIAL TRANSMISSION SYSTEMS - DAB
(3) Synergies with Digital Television
Although the DVB systems (e.g., DVB-S, DVB-C and DVB-T) were primarily
designed for television broadcasting, they can and do provide radio (audio-only)
programs. DVB-T is a proven technology for digital television and has been
implemented in many countries. As DAB, DVB-T is, technically speaking,
sufficiently flexible to allow for delivery to portable and mobile receivers.
Challenges with implementing DVB-T for digital radio centre on the need for good
mobile and portable reception and its large bandwidth usage. DVB-T is not
optimised for mobile reception and no mobile or portable hand held receivers are
as yet available. The high data rates and wide bandwidth needed to operate the
system not only increases power consumption but also makes the design of
battery-powered devices difficult. The large bandwidth use required for DVB-T
means that many services must be multiplexed together for efficient use of the
spectrum and there is a risk that such multiplexes may not be fully utilised, thereby
leading to inefficient spectrum use.
Experience suggests that DVB-T platforms designed primarily for digital television
are increasingly likely to carry audio-only entertainment and information as well.
Most current implementations of DVB-T services for digital television target fixed
reception. Consumer-grade mobile DVB-T receivers are likely to be produced with
the aim of providing mobile television and multimedia services.
From the technical perspective, DAB and DVB-T are both using the same
modulations: OFDM. Therefore it will not be surprising to see common DAB/DVB-T
chips developing rapidly. Frontier Silicon announced that they are planning to
develop a single chip DVB-T and DAB decoder termed "Logie," for which they have
already signed a number of customers.
4.2.6 Future Developments of DAB
The technical developments of the DAB system go into two directions:
• associate audio services with flexible multimedia services including moving pictures
• multi-channel audio
• enhanced audio codec, DAB+
(1) DAB-Based Multimedia Broadcast Systems (DMB) T-DMB
Digital Multimedia Broadcasting (DMB) uses an MPEG-2 TS with additional error
protection (Reed-Solomon (188,204) code and interleaving as specified for DVB
services) transmitted in a DAB Stream Mode sub-channel. Bosch originally
proposed the use of MPEG-2 TS to carry one video service in a DAB Ensemble.
Subsequently there were proposals by Bosch and the collaborative project MINT
(funded by German BMBF) to use MPEG-4 video coding to fit several video
services in a DAB Ensemble. Later there was further development and promotion
of T-DMB in Korea, and a parallel development of the S-DMB system for satellite
BTH. T-DMB specifications were approved by WorldDAB (December 2004) and
were standardized at ETSI (June 2005).
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DIGITAL RADIO GUIDE TERRESTRIAL TRANSMISSION SYSTEMS - DAB
T-DMB receiving devices have become available and are integrated within mobile
phones, in portable PCs and small screen portable devices. Several pilot trials and
projects are ongoing in Korea, UK, Germany, France and elsewhere. It should be
noted that Korea has deployed both Satellite (S-) and Terrestrial (T-) DMB,
although these have limited technical similarities leading to very different terminal
devices. T-DMB was introduced in Korea in mid-2005 using an existing terrestrial
network in Band III (although formal commercial launch has been delayed whilst
business issues are coordinated). Frequencies in L-Band are available in much of
Europe for possible use with DMB and DAB.
European T-DMB was officially launched on 7 June 2006 in Munich on the
occasion of the World Football Cup. The launch was organized by WorldDAB and
its partners.
(a) IP over Enhanced Packet Mode
Enhanced Packet Mode (EPM) provides additional error protection for DAB
packet mode-based services, such as IP and MOT (Multimedia Object
Transfer), by the use of a DAB-FEC frame and the addition of FEC packets
(in a similar way to the DVB-H MPE-FEC). The same Reed-Solomon code is
used as in DMB. Interleaving is different from T-DMB and allows backwardscompatible reception of EPM services on receivers with conventional DAB
packet mode. The EPM specification has been submitted to ETSI.
(b) DAB-IP
The BT Movio's "DAB-IP" system is a DAB application of IP over Enhanced
Packet Mode. Technical trials in UK by British Telecom started mid-2005 and
ran through to the end of December 2005. Microsoft’s solution for video and
audio coding as well as digital rights management (DRM) have been
selected for this pilot. The electronic programme guide (EPG) designed for
BT Movio and standardized by ETSI proved quite successful. DAB-IP
enables DAB digital radio to share multiplex capacity with mobile TV and
therefore allows TV operators to benefit from the considerable DAB spectrum
and infrastructure investments that have been made across Europe. The
prototype DAB-IP devices were based on a fully functioning 2.5G mobile
phone which included an integrated DMB receiver, so that users could enjoy
broadcast digital TV and radio services using advanced EPG.
(c) The German DXB Project
Digital Extended Broadcasting (DXB) is a German-funded project running
until 2007. The DXB concept will offer similar services to DVB-H over a DABbased transmission system. Services may use the IP-protocol over
Enhanced Stream Mode (using MPEG-2 TS as with DMB) or via the
Enhanced Packet Mode.
It should be observed that an alternative broadcast system for mobile
multimedia applications is being developed in the framework of the DVB
Project: DVB-H (H stands for handheld). Some EBU research institutes are in
the process of looking into the technical and operational merits of DVB-H and
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DIGITAL RADIO GUIDE TERRESTRIAL TRANSMISSION SYSTEMS - DAB
DAB. Notwithstanding the results of such a study, it should be remembered
that the ultimate choice may not necessarily be taken on purely the technical
grounds. The history teaches us that not always the best technology wins, as
the business interests may sometimes be more important (e.g., VHS versus
Betamax about VCR technology).
(2) DAB as carrier of multichannel audio
Concerning multi-channel audio, many EBU broadcasters would like to see it
introduced not only in the satellite and cable systems but also in terrestrial DAB
and DVB-T systems. To this end, the EBU Broadcast Management Committee set
up a Focus Group B/MCAT (Multi-Channel Audio Transmission) which is due to
start its work in February 2004 . The EBU Village at IBC 2003 in Amsterdam
staged a very successful demonstration of some pre-recorded multi-channel
material (such as the famous production of Österreichischer Rundfunk's New Year
Concert from Vienna) as well as some live broadcasts over the Astra satellite
prepared by Bayerischer Rundfunk.
Some argue that multi-channel audio is more appropriate for television, particularly
as an adjunct to enhanced TV or HDTV, and less so for radio. The DVB system
has recently been extended to be able to accommodate not only MPEG-2 multichannel audio but optionally Dolby Digital (AC3) and Digital Theatre System (DTS),
with the proviso that further hooks for other systems such as AAC may follow.
Others believe that multi-channel audio could enhance users' experience in the
radio environment significantly and make DAB even more popular, not only in the
home environment but also (or especially) in the car. Many consider that multichannel DAB could be branded as the future "high definition" radio and could
differentiate DAB from FM to drive new business models and make it more
attractive for the general public.
There are several possible scenarios how multi-channel audio could be brought
into the DAB system efficiently and in a backwards-compatible manner. For
example, one possible solution (not necessarily the best) would be to code the
basic stereo in the existing standard MPEG 1/2 Layer II and the "surround"
component in AAC. The downside is that multi-channel sound requires more
spectrum - which is a very scarce resource indeed, and requires new production
facilities and increases the production costs.
At IBC 2003, Microsoft, Capital Radioplc, NTL Broadcast and RadioScape
announced that they planned to conduct a trial broadcast of 5.1-channel surround
sound audio signals over DAB in the central London area. This trial started in
October 2003 and involves live IP data casting of Widows Media Audio 9
Professional (WMA Pro) content coded at 128 kbps over L-Band frequencies.
(3) Enhanced Audio Codec, DAB+
This enhancement to DAB formally was published as an ETSI standard on 12
February 2007 (ETSI, TS 102563 V1.1.1).
The new audio codec MPEG-4 HE-AAC v2 offers broadcasters much higher
bandwidth efficiency which results in significant cost savings per channel and the
possibility to broadcast more channels in a multiplex than before.
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DIGITAL RADIO GUIDE TERRESTRIAL TRANSMISSION SYSTEMS - DAB
New receivers which appear on the market with the new codec will also be
backwards compatible with the existing DAB-MPEG Audio Layer II in operation
today for DAB services.
The main features for the new audio codec are described by WorldDAB as:
• Latest MPEG-4 audio codec delivers exceptional performance efficiency;
• More stations can be broadcast on a multiplex;
• Greater station choice for consumers;
• More efficient use of radio spectrum;
• Lower transmission costs for digital stations;
• New receivers backwards compatible with existing codec standard;
• Current MPEG Audio Layer II services and consumers unaffected;
• Compatible with existing scrolling text and multimedia services;
• Robust audio delivery with fast re-tuning response time;
• Optimised for live broadcast radio;
• Broadcasters/regulators can select either standard MPEG Audio Layer II, or
optional high efficiency advanced audio codec, or both, to suit their country
needs.
The following is a brief explanation of how the new codec enhances the DAB
standard.
The main Digital Audio Broadcasting specification (ETSI EN 300 401) defines how
audio should be broadcast. “The DAB system uses MPEG Audio Layer II, suitably
formatted for DAB transmissions. For 48kHz sampling frequency it uses ISO/IEC
11172-3 and for 24kHz sampling frequency it uses ISO/IEC 13818-3.”
For Layer II audio, two sampling rates are permitted, 48 kHz and 24 kHz. Each
audio frame contains samples for 24 ms or 48 ms respectively and each contains
the same number of bytes. The audio frames are carried in one or two respectively
DAB logical frames. The draft technical specification now approved by ETSI
defines the way that audio (programme) services are carried when using MPEG 4
HE AAC v2. For AAC, two transforms are specified. For DAB, only the 960
transform is permitted with sampling rates of 48 kHz, 32 kHz, 24 kHz and 16 kHz.
Each AU (audio frame) contains samples for 20 ms, 30 ms, 40 ms or 60 ms
respectively. In order to provide a similar architectural model to Layer II audio,
simple synchronisation and minimal re-tuning delay (i.e. station selection, or
“zapping” time), AUs are built into audio super frames of 120 ms which are then
carried in five DAB logical frames. In order to provide additional error control, Reed
Solomon coding and virtual interleaving is applied. The overall scheme is shown in
Figure 4.3.
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