Digital Audio Broadcasting - DAB - Digital Video and Audio Broadcasting Technology - page 465

combined to form one data stream. In the present case, the ensemble given
the exemplary name "Digital Radio 1" is composed of 4 programs, the so-
called services, here having the designations "P1", "BR1", "BR3" and
"P2". These services, in turn, can be composed of a number of service
components. A service component can be, e.g. an audio stream or a data
stream. In the example, the service "P1" contains an audio stream, "Au-
dio1". This audio stream is physically transmitted in subchannel SC1.
"BR" is composed of an audio stream "Audio2" and a data stream "Data1"
which are broadcast in subchannels SC2 and SC3. Each subchannel has a
capacity of n • 8 kbit/s. The transmission in the subchannels is completely
synchronous, i.e. the order of the subchannels is always the same and the
data rates in the subchannels are always constant. All subchannels together
- up to a possible maximum of 64 - result in the so-called Common Inter-
leaved Frame. Service components can be associated with a number of
services, e.g. as in the example "Data2".
During their transmission in the DAB system, the different subchannels
can be provided with different degrees of error protection (unequal FEC).

SC1

FEC 1

ETI

SC2

RF

FEC 2

…

SCn

FEC n

SC =
subchannel
(up to 64)

DAB modulator

Fig. 26.5. DAB modulator

The data stream generated in the DAB multiplexer is called ETI (En-
semble Transport Interface). It contains all programs and contents to be
broadcast later via the DAB transmitter. The ETI signal can be supplied to
the modulator from the playout center, e.g. via optical fiber links via exist-
ing telecommunication networks or by satellite. A suitable link for this
purpose is an E1 link having a data rate of 2.048 Mbit/s.