Digital Audio Broadcasting - DAB - Digital Video and Audio Broadcasting Technology - page 487

For this reason there is another passive bandpass filter (mask filter).
Without pre-correction a DAB signal would have a shoulder attenuation of
about 30 dB. If the pre-correction has been properly set the shoulder at-
tenuation will be about 40 dB. This would still interfere with the adjacent
channels and would not be authorised by the Authorities. Following the
mask filter the shoulders are then lowered by another 10 dB.
Fig. 26.22. shows frequently used DAB blocks. A VHF channel (7 MHz
bandwidth) is divided into 4 DAB blocks. The blocks are then called e.g.
block 12A, 12B, 12C or 12D.
Tables 26.6., 26.7. and 26.8. list the channel tables used in DAB. Each
DAB channel has a width of 7/4 MHz = 1.75 MHz. However, the COFDM
signal bandwidth is only 1.536 MHz and there is thus a guard band for the
adjacent channels.

26.6 DAB Data Structure

In the section following the essential features of the data structure of DAB
will be explained. In DAB, a number of MPEG-1 or -2 Audio Layer II
coded audio signals (MUSICAM) combined to form an ensemble are
transmitted in a 1.75 MHz-wide DAB channel. The maximum net data rate
of the DAB channel is about 1.7 Mbit/s and the gross data rate is 2.4
Mbit/s. The data rate of an audio channel is between 32 and 384 kbit/s.

Service b Service c

32…384 kbit/s

Service a

32…384 kbit/s 32…384 kbit/s

n * 8 kbit/s

Data 1
PAD 1

Audio 1 Config 1 Audio 2 Config 2 Audio 3 Config 3

H = Header
SC = Subchannel
FIG = Fast
Information Group
PAD = Program
Associated Data
FIC = Fast
Information
Channel

STI . . .

H SC SC FIG H SC SC FIG FIG

Up to 64
subchannels
each n * 8 kbit/s

FIC SC1 SC2 SC3 SC4 … SCn

ETI

Header

MST (Main Stream Data)

Fig. 26.23. Composition of the ETI data stream