Digital Audio Broadcasting - DAB - Digital Video and Audio Broadcasting Technology - page 492

a 16-bit-wide CRC checksum. In the data area of the FIB the messages are
transmitted in so-called Fast Information Groups (FIG). Each FIG is iden-
tified by its FIG type. An FIG is composed of the FIG type, of the length
and the FIG data field in which the actual messages are transmitted.
In the main service channel (Fig. 26.28.), the individual subchannels are
broadcast. A total of 64 subchannels are possible. Each subchannel has a
data rate of n•8 kbit/s. The subchannels are associated with services (pro-
grams). The MSC is composed of so-called Common Interleaved Frames
which have a length of 24 ms and consist of Capacity Units (CU) with a
length of 64 bytes. Overall, 864 CUs result in one CIF which then has a
length of 55296 bytes. A number of CUs make up one subchannel in
which the audio frames or data are transmitted.
An ETI frame (Fig. 26.29.) is composed of the header, the Main Stream
Data (MST), and End of Frame (EOF) and the Time Stamp (TIST). An
ETI frame has a length of 24, 48 or 96 ms.

GPS

1pps
pulse

1s

Time stamp

...

ETI
header

...

Main Stream Data

TIST

Frame (24, 48, 96 ms)

Fig. 26.30. Synchronization of DAB modulators via the TIST in the ETI frame

26.7 DAB SingleFrequency Networks

In the further text, DAB single-frequency networks (SFN) and their syn-
chronisation will be discussed.
COFDM is optimally suited to single-frequency operation. In single-
frequency operation, all transmitters are operating at the same frequency
which is why single-frequency operation is very economical with regard to
frequencies. All transmitters are broadcasting an absolutely identical signal