Introduction - Digital Video and Audio Broadcasting Technology - page 2

the channels broadcast via satellite are even 36 MHz wide. It is not surpris-
ing that a new boom is being experienced especially in broadband TV ca-
ble, which is being used as a medium for high-speed home Internet access
in the Mbit/sec range, uplinking via cable modems.
The foundation stone for analog television was laid by Paul Nipkow
back in 1883 when he developed what is now known as the Nipkow disc.
He had the idea of transmitting a picture by dividing it into lines. The first
real analog TV transmissions per se took place in the thirties but, held back
by World War II, analog television didn't have its proper start until the fif-
ties, in black and white at first. The television set acquired colour towards
the end of the sixties and from then on, this technology has been basically
only refined, both in the studio and in the home. There have been no fur-
ther changes in the principles of the technology. Analog TV transmissions
are often so perfect, at least in quality if not in content, that it is difficult to
interest many people in buying a receiver for digital TV.
In the eighties, an attempt was made to depart from traditional analog
TV by way of D2MAC. For various reasons, this did not succeed and
D2MAC vanished from view again. In Europe, the PAL system was given
a slight boost by the introduction of PALplus but this, too, did not achieve
much success in the TV set market, either. At the same time, various ap-
proaches were tried, mainly in Japan and in the US, to achieve success
with the transmission of HDTV, but these also failed to gain the universal
popular appeal hoped for.
In the studio, digital television signals have been used since the begin-
ning of the nineties as uncompressed digital TV signals conforming to
“CCIR 601”. These data signals have a date rate of 270 Mbit/sec and are
highly suitable for distribution and processing in the studio, and are very
popular today. But they are not at all suitable for broadcasting and trans-
mission to the end user. The channel capacities available via cable, terres-
trial channels and satellite would not be even nearly adequate enough for
these signals. In the case of HDTV signals, the data rate is over 800
Mbit/sec uncompressed. Without compression, these signals could not be
broadcast.
The key event in the field of digital television can be considered to be
the establishment of the JPEG standard. JPEG stands for Joint Photo-
graphic Experts Group, a group of experts specializing in still frame com-
pression. It was here that the Discrete Cosine transform (DCT) was used
for the first time for compressing still frames towards the end of the eight-
ies. Today, JPEG is a commonly used standard in the data field and is be-
ing used very successfully in the field of digital photography. Digital cam-
eras are experiencing quite a boom and are becoming better and better so