Digital TV Standards
• All digital TV variants can carry both standarddefinition television (SDTV) and high-definition
television (HDTV).
• SDTV digital television systems derive much of their
structure from the need to be compatible with analog
television.
• In particular, the interlaced scan is a legacy of analog
television.
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• Attempts were made during the development of
digital television to prevent a repeat of the
fragmentation of the global market into different
standards (that is, PAL, SECAM, NTSC).
• However, once again, the world could not agree on a
single standard, and, hence, there are three major
standards in existence: the European DVB system
and the U.S. ATSC system, plus the Japanese
system ISDB.
• In addition, for example Korea has adopted S-DMB
for satellite mobile broadcasting and China has
announced DMB-T/H.
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• DVB, short for Digital Video Broadcasting, is a suite
of internationally accepted open standards for digital
television.
• DVB standards are maintained by the DVB Project,
an industry consortium with more than 270 members,
and they are published by a Joint Technical
Committee (JTC) of European Telecommunications
Standards Institute (ETSI), European Committee for
Electrotechnical Standardization (CENELEC) and
European Broadcasting Union (EBU).
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• DVB systems distribute data using a variety
approaches, including by satellite (DVB-S, DVB-S2),
cable (DVB-C), terrestrial television (DVB-T) and
terrestrial television for handhelds (DVB-H).
• These standards define the physical layer and data
link layer of the distribution system.
• Devices interact with the physical layer via a
synchronous parallel interface (SPI), synchronous
serial interface (SSI), or asynchronous serial
interface (ASI).
• All data is transmitted in MPEG-2 transport streams
with some additional constraints.
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• These distribution systems differ mainly in the
modulation schemes used, due to the different
technical constraints.
• DVB-S uses QPSK, 8PSK or 16-QAM.
• DVB-S2 uses QPSK, 8PSK, 16APSK or 32APSK, at
the broadcasters decision. QPSK and 8PSK are the
only versions regularly used.
• DVB-C (VHF/UHF) uses QAM: 16-QAM, 32-QAM,
64- QAM, 128-QAM or 256-QAM.
• Lastly, DVB-T (VHF/UHF) uses 16-QAM or 64-QAM
(or QPSK) in combination with COFDM and
hierarchical modulation.
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• The DVB Multimedia Home Platform (DVB-MHP)
defines a Java-based platform for the development of
consumer video system applications.
• In addition to providing abstractions for many DVB
and MPEG-2 concepts, it provides interfaces for
other features like network card control, application
download, and layered graphics.
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• The Advanced Television Systems Committee
(ATSC) is the group that developed the ATSC digital
television standard for the United States, and some
other countries have also adopted it.
• The ATSC standards are intended to replace the
NTSC system used mostly in North America.
• Many aspects of ATSC are patented, including
elements of the MPEG video coding, the AC-3 audio
coding, and the 8-VSB modulation.
• As with other systems, ATSC depends on numerous
interwoven standards.
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• For transport, ATSC uses the MPEG-2 Systems
specification, known as Transport stream, to
encapsulate data, subject to certain constraints.
• ATSC uses 188-byte MPEG transport stream packets
to carry data.
• Before decoding of audio and video takes place, the
receiver must demodulate and apply error correction
to signal.
• Then, the transport stream may be demultiplexed into
its constituent streams.
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• Dolby Digital AC-3 is used as the audio codec,
though it was officially standardized as A/52 by the
ATSC.
• It allows the transport of up to five channels of sound
with sixth channel for low-frequency effects (the socalled 5.1 configuration).
• ATSC signals are designed to use the same 6 MHz
bandwidth as NTSC television channels.
• Once the video and audio signals have been
compressed and multiplexed, the transport stream
can be modulated in different ways depending on the
method of transmission.
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• Terrestrial broadcasters use 8-VSB modulation that
can transfer at a maximum rate of 19.39 Mbits/sec,
sufficient to carry several video and audio programs
and metadata.
• Cable television plants generally operate at a higher
signal-to-noise ratio and can use 16-VSB or 256QAM to achieve a throughput of 38.78 Mbits/sec,
using the same 6 MHz channel.
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• Integrated Services Digital Broadcasting (ISDB) is the
digital television and digital audio broadcasting format
that Japan has created to allow radio and television
stations there to convert to digital.
• ISDB is maintained by the Japanese organisation
ARIB.
• The core standards of ISDB are ISDB-S (satellite
television), ISDB-T (terrestrial), ISDB-C (cable) and
2.6 GHz band mobile broadcasting which are all
based on MPEG-2 video and audio coding as well as
the transport stream described by the MPEG-2
standard, and are capable of high definition television
(HDTV).
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• ISDB has adopted the MPEG-2 video and audio
compression system.
• The various flavours of ISDB differ mainly in the
modulations used, due to the requirements of
different frequency bands.
• The 12 GHz band ISDB-S uses PSK modulation and
ISDB-T (in VHF and/or UHF band) uses COFDM with
PSK/QAM.
• Some comparisons have been made in the Figure 1.
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Systems
Video
Audio
ATSC 8-VSB
DVB COFDM
ISDB BST-COFDM
Main profile syntax of ISO/IEC 13818-2 (MPEG-2 video)
ATSC Standard
ISO/IEC 13818-2 (MPEG-2
ISO/IEC 13818-7 (MPEG-2
A/52 (Dolby AC-3) layer II audio) and Dolby AC-3
- AAC audio
Transmission system
Channel coding
Outer coding
Outer
interleaver
Inner coding
Inner
interleaver
Data
randomization
Modulation
R-S (207, 187,
t=10)
52 R-S block
interleaver
Rate 2/3 trellis
code
R-S (204, 188, t=8)
12 to 1 trellis code
interleaver
12 R-S block interleaver
Punctured convolutional code: Rate 1/2, 2/3, 3/4, 5/6, 7/8
Constraint length=7, Polynomials (octal)=171, 133
Bit-wise interleaving,
Bit-wise interleaving and
frequency interleaving and
frequency interleaving
selectable time interleaving
16-bit PRBS
16-bit PRBS
16-bit PRBS
COFDM QPSK, 16-QAM and
64-QAM.
Hierarchical modulation: multiresolution constellation (16-QAM
and 64-QAM). Guard interval
1/32, 1/16, 1/8 & 1/4 of OFDM
8-VSB and 16-VSB symbol, 2 modes: 2k and 8k FFT
BST-COFDM with 13 frequency
segments DQPSK, QPSK, !6QAM and 64-QAM.
Hierarchical modulation: choice
of three different modulations
on each segment. Guard interval:
1/32, 1/16, 1/8 & 1/4 of OFDM
symbol. 3 modes: 2k, 4k
and 8k FFT
Figure 1. Some characteristics of the three DTV systems.
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