Atec Rohde-Schwarz-SFQ Series - Manual (Page 8)

8 TV Test Transmitter R&S ® SFQ
ISDB-T: coding and mapping for
antenna
The ISDB-T (terrestrial integrated services
digital broadcasting) coder of the R&S
SFQ encodes an MPEG-2 data stream in
line with standards for transmission in
the RF channel. The transport stream first
passes through the outer coder where
each transport stream packet undergoes
Reed-Solomon encoding. The receiver is
thus able to correct up to eight errored
bytes in one transport stream packet.
The error-protected data stream then pas-
ses through a splitter which divides the
transport stream packets between as
many as all three hierarchical layers. The
subsequent energy dispersal module
adds a pseudo random binary sequence
(PRBS) to the data stream to ensure a suf-
ficient number of binary changes.
Depending on the two transmission para-
meters "modulation" and "code rate", a
varying delay of the data stream in the
three paths is obtained through bytewise
interleaving in the transmitter and de-
interleaving in the receiver. Delay adjust-
ment is performed in the coder to mini-
mize the technical effort at the receiver
end. In this module, the three data
streams are delayed so that subsequent
delay differences can be compensated for
beforehand.
Bytewise interleaving separates initially
adjacent bytes and thus makes the signal
resistant to burst errors.
The convolutional coder with integrated
puncturer adds further redundancy to the
data stream to permit error correction in
the receiver (Viterbi decoder). The code
rate can be selected according to the
required transmission characteristics of
the system.
Modulation comes next. It includes bit-
wise interleaving with delay adjustment
and mapping to the modulation constella-
tion diagram. Possible ISDB-T constella-
tions are DQPSK, QPSK, 16QAM and
64QAM. The constellation can be selec-
ted according to the required transmis-
sion characteristics of the system. Appro-
priate bitwise interleaving and delay
adjustment are automatically selected.
The hierarchical data stream is then syn-
thesized. For this purpose, the complex
mapped data from each of the three
paths is added to form a serial data
stream.
Synthesis is followed by symbol-by-
symbol time interleaving which is perfor-
med by an intra-segment time interleaver
Status menus
8 VSB
ISDB-T