Page 85 - DCAP303_MULTIMEDIA_SYSTEMS

Unit 5: Video

do not have DTV broadcasting yet but have already decided which standard to follow. Just like notes
analogue TV has its “standards war” (NTSC, PAL, SECAM, etc.) so does have the DTV.

There are following three DTV transition standards in the world:
1. ATSC adopted by the USA, Canada, Mexico and South Korea;
2. ISDB-T adopted by Japan;

3. DVB-T (Digital Video Broadcast Terrestrial), adopted by the other countries that have already
decided which DTV standard they will follow, like the countries located in Europe, Asia,
Africa and Oceania.
All three DTV transmitting system uses the MPEG-2 algorithm to encode the image, the same
algorithm used by DVD. The differences between them are the video format before the encoding,
the video format after encoding and the way audio in encoded. The ATSC system uses a technique
called 8-VSB while the other two systems use a technique called COFDM, which is less sensitive
to noise.
Apparently the fact of ATSC being the standard most sensitive to noise, does not bother the
US market, where few people still watch terrestrial TV (i.e., using antennas). Which makes us
think if the ATSC standard was the best choice for Mexico. On the other hand, Mexico is a part
of NAFTA (North American Free Trade Association), which makes the country one of the main
product manufacturers and exporters to the US. Thus, we believe that the adoption of the same
standard as the US was more commercial wise than technical.
rise of Digital Compression
Since 1972, International Telecommunication Union’s radio telecommunications sector (ITU-R) has
been working on creating a global recommendation for analogue HDTV. These recommendations
however did not fit in the broadcasting bands which could reach home users. The standardization
of MPEG-1 in 1993 also led to the acceptance of recommendations ITU-R BT.709. In anticipation
of these standards the Digital Video Broadcasting (DVB) organisation was formed, an alliance
of broadcasters, consumer electronics manufacturers and regulatory bodies. The DVB develops
and agrees on specifications which are formally standardised by ETSI.

The DVB created first the standard for DVB-S digital satellite TV, DVB-C digital cable TV and
DVB-T digital terrestrial TV. These broadcasting systems can be used for both SDTV and HDTV.
In the US, the Grand Alliance proposed ATSC as the new standard for SDTV and HDTV. Both
ATSC and DVB were based on the MPEG-2 standard. The DVB-S2 standard is based on the newer
and more efficient H.264/MPEG-4 AVC compression standards. Common for all DVB standards
is the use of highly efficient modulation techniques for further reducing bandwidth, and foremost
for reducing receiver-hardware and antenna requirements.

In 1983, the International Telecommunication Union’s radio telecommunications sector (ITU-R) set
up a working party (IWP11/6) with the aim of setting a single international HDTV standard. One
of the thornier issues concerned a suitable frame/field refresh rate, the world already having split
into two camps, 25/50 Hz and 30/60 Hz, related by reasons of picture stability to the frequency
of their main electrical supplies.
The IWP11/6 working party considered many views and through the 1980s served to encourage
development in a number of video digital processing areas, not least conversion between the two
main frame/field rates using motion vectors, which led to further developments in other areas.
While a comprehensive HDTV standard was not in the end established, agreement on the aspect
ratio was achieved.
Initially the existing 5 : 3 aspect ratio had been the main candidate but, due to the influence
of widescreen cinema, the aspect ratio 16:9 (1.78) eventually emerged as being a reasonable
compromise between 5 : 3 (1.67) and the common 1.85 widescreen cinema format. (Bob Morris

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