Introduction - Digital Video and Audio Broadcasting Technology - page 3

that this medium may well replace traditional photography in many areas
in the foreseeable future.
The DCT also became the basic algorithm for MPEG, the Motion Pic-
ture Experts Group, which developed the MPEG-1 standard by 1993 and
then the MPEG-2 standard. The aim of MPEG-1 was to achieve the repro-
duction of full-motion pictures at data rates of up to 1.5 Mbit/sec, using the
CD as a data medium. The aim for MPEG-2 was higher and MPEG-2, fi-
nally, was to become the baseband signal for digital television world-wide.
Initially, only Standard Definition Television (SDTV) was provided for in
MPEG-2, but High Definition Television (HDTV) was also implemented
which was apparently originally intended for MPEG-3. However, there is
no MPEG-3 (nor does it have anything to do with MP3 files, either). In
MPEG-2, both the MPEG data structure was described (ISO/IEC 13818-1)
and a method for full-motion picture compression (ISO/IEC 13818-2) and
for audio compression (ISO/IEC 13818-3) defined. These methods are
now used throughout the world. MPEG-2 allows the digital TV signals of
originally 270 Mbit/sec to be compressed to about 2 to 6 Mbit/sec. The un-
compressed data rate of a stereo audio signal of about 1.5 Mbit/sec, too,
can be reduced to about 100 to 400 kbit/sec. As a result of these high com-
pression factors it is now possible even to combine a number of programs
to form one data signal which can then be accommodated in what was
originally an e.g. 8 MHz-wide analog TV channel. Meanwhile, there is
MPEG-4, MPEG-7 and MPEG-21.
At the beginning of the nineties, Digital Video Broadcasting (DVB) was
then created as a European project. In the course of this project, three
transmission methods were developed: DVB-S, DVB-C and DVB-T, now
also including DVB-H and DVB-S2. The satellite transmission method
DVB-S has been in use since about 1995. Using the QPSK method of
modulation and with channel bandwidths of about 33 MHz, a gross data
rate of 38 Mbit/sec is possible with satellite transmission. With approxi-
mately 6 Mbit/sec per program, up to 6, 8 or even 10 programs can now be
transmitted in one channel depending on data rate and content and when
mainly audio programs are broadcast, more than 20 programs are often
found in one channel. In the case of DVB-C, transmitted via coaxial cable,
the 64QAM modulation also provides a data rate of 38 Mbit/sec at a
bandwidth of only 8 MHz. DVB-C, too, has been in use since about 1995.
The digital terrestrial TV system DVB-T started in 1998 in Great Britain in
2K mode and is now available nationwide. This terrestrial path to broad-
casting digital TV signals is being used more and more, spreading from the
UK, Scandinavia and Spain all the way to Australia. DVB-T provides for
data rates of between 5 to 31 Mbit/sec and the data rate actually used is
normally about 20 to 22 Mbit/sec if a DVB-T network has been designed