For those of you interested in TV broadcast standards a few
bullet-points:
- It can be expected that the analog broadcasting systems NTSC/PAL/SECAM
will be deactivated worldwide within the next two decades. The UK in
particular has already specific plans to shut down PAL broadcasting
by 2010.
- A new global standard called DVB (Digital Video Broadcast) has
been developed since the mid 1990s. It is based on
- MPEG2 audio and video stream compression
- Three modem standards optimized for different media:
DVB-S for direct satellite reception
DVB-C for cable distribution
DVB-T for terrestrial reception
The modulation standards are different in order to take account
of the different channel properties (satellite requires
constant amplitude, is very noisy and offers wide bandwidth,
terrestrial requires narroe bandwidth and is prone to selective
fading and echos, cable is low noise and low echo, but also low
bandwidth). Nevertheless, their design is closely aligned, e.g.
they use the same forward error correction scheme with only slightly
different parameters to simplify the design of chips that support
all alternatives.
- Various auxiliary meta-data standards, such as DVB-SI (System
Information) which annotates the bitstreams with electronic program
guide data in order to allow rather comfortable channel selection and
recorder programming.
Although DVB was originally a project sponsored by the European
Broadcast Union (EBU) and the European Telecommunications Standards
Institute (ETSI), it has become almost a defacto global standard as
almost all new digital broadcasting projects in Europe, Australia,
Africa, and Asia are based on DVB. The DVB-S standard for digital
satellite broadcast has been accepted as a world-wide standard by the
International Telecommunications Union (ITU, the UN body in charge of
the wordwide coordination of use of the radio spectrum).
Only the US and Japan have decided to use incombatible systems. Some of
the digital satellite and cable systems used in the US also use DVB-S
and DVB-C modulation, but the FCC has made a rather controversial
selection of a VSB modulation technique instead of the significantly
more sophisticated and robust DVB-T scheme for terrestrial broadcasting.
The US ADTV standard is also using MPEG2 for the video compression, but
uses US-only standards for every other aspect of the system design
(modem, electronic program information, system parameters, etc.).
Comparisons between the VSB modulation and the DVB-T scheme performed in
the US have resulted in significantly lower reception reliability with
indoor antennas under comparable conditions.
Some more info on the DVB standards is on
http://www.cl.cam.ac.uk/~mgk25/dvb.txt
Markus
--
Markus G. Kuhn, Computer Laboratory, University of Cambridge, UK
Email: mkuhn at acm.org, WWW: <http://www.cl.cam.ac.uk/~mgk25/>
