Digital Signal Processing Reference
In-Depth Information
Program1
Program 2
Program n
Data
Text
Pictures
SC FIC
MSC
SC
: Synchronisation Channe,
FIC
: Fast Information Channel,
MSC
: Main Service Channel
Synchronisation
Controlling
Data
6 Stereo audio channels are normally transmitted simultaneously in a DAB frame .
1,536 MHz
f
0
f
ZF
-768 kHz
f
ZF
f
ZF
-768 kHz
Within the DAB bandwidth of 1,536 MHz 2,4 MBit/s are transmitted . In the mode I 1536 carrier
frequencies at intervals of 1 kHz are used, which are 4-DPSK modulated in each case
Superposition of all 1536
sine carriers within Ts
T
G
=
0,246 ms
T
N
= 1 ms
T
S
= 1,246 ms
User and protection range of a DAB symbol .
The DAB symbol time interval takes a total of 1,246 ms. It consists of the protection
interval and the user intervall . A DAB schedule contains 76 such symbols of Ts= 1,246
ms. Per symbol 4 states (4-DPSK) - and therefore 2 bit - can be represented per carrier
frequency . Per schedule (94,7 ms) these are at 1536 carrier frequencies 1536 *76 * 2 =
233 .472 bit, per second 2,4 MBit or a transmission rate of 2,4MBit/s results.
TV-channel 11
TV-channel 12
TV-channel S11
4 TV programs
DAB
4 TV programs
Video signal
A
B
C
D
Video signal
f
Four DAB signals can be transmitted within a television channel with 7 MHz bandwidth .
This corresponds to 24 Stereo programs in CD quality or 80 mono programs . For example
the channel 12 in the VHF range is used for pilot projects . Every one of the four DAB
signals can be replaced by 1 TV-program .
Illustration 277:
DAB-frame, frequency- and time structure
The synchronization component SC contains a zero symbol which enables the receiver to conduct a coarse
synchronization of the frame and the symbol structure. The phase reference symbol which is also contained
in the synchronization part serves to conduct a precise synchronization. The control component FIC trans-
mits data to control and decodes the DAB multiplex signal. As these data require error-free transmission
they have been specially coded to avoid errors.
The signal received is only evaluated during the time that the interval is used T
N
. The protective interval
with the length T
G
reduces (linear) distortions caused by multipath and synchronized reception. The data
component MSC contains the user data.
