Digital Audio Broadcasting - DAB - Digital Video and Audio Broadcasting Technology - page 481

lowing data: the FIC is protected equally with a mean code rate of 1/3. The
data of the packet mode can be provided with a code rate of 2/8, 3/8, 4/8 or
6/8.
The MPEG audio packets are protected with unequal error protection
which is also controllable in DAB. Some components of the MPEG audio
packet are more sensitive to bit errors than other ones.
The components in the DAB audio frame which are provided with dif-
ferent error protection are:

• Header

• Scale factors

• Subband samples

•

Program-associated data (PAD)

The header must be protected particularly well. If errors occur in the
header, this will lead to serious synchronization problems. The scale fac-
tors must also be well protected since bit errors in this area would make for
very unpleasant listening. The subband samples are less sensitive and their
error protection is correspondingly lower.

PI = Puncturing Index

24

Puncturing index PI1, PI2, PI3, PI4 depending
on protection level (1,2,3,4,5) and audio bitrate
(ETS 300401, page 158)
protection level 1 = highest protection,
5 = lowest protection

PI1

PI2

PI4

PI3

Subband samples

1

time

DAB audio frame

Coderate = 8/(8+PI); PI = 1…24;

Fig. 26.20. Unequal forward error correction of a DAB audio frame

Fig. 26.20. shows an example of the unequal error protection within a
DAB audio frame. The puncturing index describes the quality of the error