MC92314 Datasheet, PDF (22/100 Pages) Motorola, Inc – DVB-T Single Chip Demodulator Application Note

Device Description
Freescale Semiconductor, Inc.
C_Proportional
VCXO
Phase
Detector
Integra-
tor
sd-DAC
C_Integrator
tion _LPF
rma _{Figure 3-4. Time Synchronisation of the OFDM Block}
Info ^{3.2.2.4 Channel Estimation}
To compensate for the impairments of the terrestrial channel it is essential to estimate the
ry channel transfer function. This estimation is done using the scattered and continual pilot carriers.
a As the scattered pilots change in subsequent OFDM symbols a time interpolation over 4 OFDM
in ^{symbols is necessary to build a complete set of pilot information. This set contains one valid pilot}
sample at every 3rd carrier position. To obtain a channel estimation value so the set ends up with
lim ^{an estimation value for each carrier position, frequency interpolation must be performed.}
e 3.2.2.5 Channel Estimation RAM
Pr ^{The channel estimation RAM must store the data carriers until the channel estimation is available}
for a given OFDM symbol.
3.2.2.6 Channel Correction
In the channel correction block the estimate of the channel transfer function is used to
compensate the influence of the terrestrial transmission. In principle each data carrier’s value is
multiplied with the inverse of the estimate to approximate the desired flat overall frequency
response to as close as possible.
3.2.2.7 Channel State Estimation
To improve the efficiency of the decoding of the inner convolutional code, information about the
reliability of each bit received via the transmission channel, is generated during the demodulation
process. So data that were transmitted in subchannels disturbed heavily due to echoes or
interference (resulting in a low SNR in these specific subchannels) are marked less reliable than
those transmitted in nearly undisturbed subchannels. In the channel state estimation this
MOTOROLA
3-4
Single Chip DVB-T Demodulator - Rev. 1.3 (11/30/98)
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