Digital Audio Broadcasting - DAB - Digital Video and Audio Broadcasting Technology - page 484

Inverse Fast Fourier Transform. After that, we are back in the time domain
where the guard interval is added to the symbol by repeating the end of the
symbol following.

GPS

ETI

Freq.
inter
leaver

Input
interface

Delay
comp.

Different.
mapper

FEC

Guard
interval
insertion

Frame
gen.

Pre
correction

IFFT FIR

IQ mod.
IF/RF up.

Fig. 26.21. Block diagram of a DAB modulator and transmitter

216.928
MHz

218.640
MHz

220.352
MHz

222.064
MHz

223.936
MHz

225.648
MHz

227.360
MHz

229.072
MHz

A B C D A B C D

f
[MHz]

Channel 12

Channel 11

230
MHz

216
MHz

223
MHz

Band III: 174 - 240 MHz
L Band: 1452 - 1492 MHz

Fig. 26.22. DAB channel allocation with channel 11 and 12 as example

After FIR filtering, pre-correction is carried out in the power transmitter
for compensating for the non-linearities of amount and phase of the ampli-
fier characteristic. The IQ modulator following is then usually the IF/RF
up converter at the same time. Today, direct modulation is normally used,
i.e. direct conversion from baseband up into RF. This is followed by power
amplification in transistor output stages. The remaining non-linearities and