Digital TV Standards

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Digital TV Standards tMyn 1

Digital TV Standards

All digital TV variants can carry both standard-

definition 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.




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 systemand 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 hasannounced DMB-T/H.




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 TelecommunicationsStandards Institute (ETSI), European Committee for

Electrotechnical Standardization (CENELEC) and

European Broadcasting Union (EBU).




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 streamswith some additional constraints.




These distribution systems differ mainly in the

modulation schemes used, due to the differenttechnical 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 theonly 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.




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.




The Advanced Television Systems Committee

(ATSC) is the group that developed the ATSC digitaltelevision 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.




For transport, ATSC uses the MPEG-2 Systems

specification, known as Transport stream, toencapsulate data, subject to certain constraints.

ATSC uses 188-byte MPEG transport stream packets

to carry data.

Before decoding of audio and video takes place, thereceiver must demodulate and apply error correction

to signal.

Then, the transport stream may be demultiplexed into

its constituent streams.




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 so-

called 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 themethod of transmission.




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 256-

QAM to achieve a throughput of 38.78 Mbits/sec,

using the same 6 MHz channel.




Integrated Services Digital Broadcasting (ISDB) is the

digital television and digital audio broadcasting formatthat 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-2standard, and are capable of high definition television

(HDTV).




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 andISDB-T (in VHF and/or UHF band) uses COFDM with

PSK/QAM.

Some comparisons have been made in the Figure 1.




Systems ATSC 8-VSB DVB COFDM ISDB BST-COFDM

Video

Audio

ATSC Standard

A/52 (Dolby AC-3)

ISO/IEC 13818-2 (MPEG-2

layer II audio) and Dolby AC-3

ISO/IEC 13818-7 (MPEG-2

- AAC audio

Channel coding

Outer coding

R-S (207, 187,

t=10)

Outer

interleaver

52 R-S block

interleaver

Inner coding

Rate 2/3 trellis

code

Inner interleaver

12 to 1 trellis code

interleaver

Bit-wise interleaving and

frequency interleaving

Bit-wise interleaving,

frequency interleaving and

selectable time interleaving

Data

randomization 16-bit PRBS 16-bit PRBS 16-bit PRBS

Modulation 8-VSB and 16-VSB

COFDM QPSK, 16-QAM and

64-QAM.

Hierarchical modulation: multi-

resolution constellation (16-QAM

and 64-QAM). Guard interval

1/32, 1/16, 1/8 & 1/4 of OFDM

symbol, 2 modes: 2k and 8k FFT

BST-COFDM with 13 frequency

segments DQPSK, QPSK, !6-

QAM 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

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

Main profile syntax of ISO/IEC 13818-2 (MPEG-2 video)

Transmission system

R-S (204, 188, t=8)

Figure 1. Some characteristics of the three DTV systems.

Digital TV Standards

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