Terrestrial Transmission of Digital Television Signals (DVB-T) - Digital Video and Audio Broadcasting Technology - page 337

In DVB-T, coherent COFDM modulation is used, i.e. the payload carri-
ers are mapped absolutely and are not differentially coded. However, this
requires channel estimation and correction for which numerous pilot sig-
nals are provided in the DVB-T spectrum and are used as test signal for the
channel estimation.

TPS
carrier

TPS
carrier

Continual
or
scattered
pilot

Continual
or
scattered
pilot

Fig. 20.3. DVB-T carriers: payload carriers, Continual and Scattered Pilots, TPS
carriers

20.2 The DVBT Carriers

In DVB-T, an IFFT with 2048 or 8192 points is used. In theory, 2048 or
8192 carriers would then be available for the data transmission. However,
not all of these carriers are used as payload carriers. In the 8K mode, there
are 6048 payload carriers and in the 2K mode there are 1512. The 8K
mode thus has exactly four times as many payload carriers as the 2K mode
but since the symbol rate is higher by a factor of exactly 4 in the 2K mode,
both modes will always have the same data rate, given the same conditions
of transmission. DVB-T contains the following types of carrier:

• Inactive carriers with fixed position (set to zero amplitude)

• Payload carriers with fixed position

• Continual pilots with fixed position

• Scattered pilots with changing position in the spectrum

• TPS carriers with fixed position