Digital Terrestrial Television according to ISDB-T - Digital Video and Audio Broadcasting Technology - page 456

25.2 ISDBT Concept

In ISDB-T, COFDM (Coded Orthogonal Frequency Division Multiplex) is
used in 2K, 4K and 8K mode (Fig. 25.1.). The 6 MHz-wide channel can be
subdivided into 13 subbands (Fig. 25.2.) in which various modulation pa-
rameters can be selected and contents transmitted. Time interleaving can
be optionally switched on in various stages. With an actual channel band-
width of 6 MHz, the useful band only has a width of 5.57 MHz, i.e. there is
a guard band of about 200 kHz each for the upper and lower adjacent
channels. One subband of the ISDB-T channel has a width of 430 kHz.
It is possible to select different types of modulation in ISDB-T:

• QPSK with channel correction

• 16QAM with channel correction

• 64QAM with channel correction

• DQPSK without channel correction (not required with DQPSK)

There are 3 possible modes (6-MHz channel example):

• Mode I , with
- 108 carriers per subband
- 3.968 kHz subcarrier spacing
- 1404 carriers within the channel
- 2048-points IFFT
• Mode II , with
- 216 carriers per subband
- 1.9841 kHz subcarrier spacing
- 2808 carriers within the channel
- 4196-points IFFT
• Mode III , with
- 432 carriers per subband
- 0.99206 kHz subcarrier spacing
- 5616 carriers within the channel
- 8192-points IFFT

As already mentioned, the full 6 MHz channel can be subdivided into 13
subbands of precisely 3000/7 kHz = 428.7 kHz each (Fig. 25.2.).
Not all of the 2048, 4192 or 8192 OFDM carriers in mode I, II or III are
actually used as payload carriers.
In ISDB-T, there are