MC92314 Datasheet, PDF (81/100 Pages) Motorola, Inc – DVB-T Single Chip Demodulator Application Note

Freescale Semiconductor, Inc.
Usage and Performance of Motorola’s Single-chip DVB-T Device
5.3.1.3 Usage of the AGC Feedback Register
The main purpose of using the AGC Feedback information is to compare different receiving
conditions (e.g. during the setup of the antenna). The differences in the AGC Feedback value
are correlated with the strength of the input signal (the lower the numbers read from the AGC
Feedback registers the lower the gain the tuner is set to).
But this holds only in the absence of interference! If interference (echoes or strong signals
in adjacent channels or a co-channel transmitter) occurs, the AGC Feedback value obviously
shows a very strong signal, but the signal strength monitored has no obvious relation to the
desired OFDM signal.
So to use the AGC information successfully it must be ensured that the antenna is adjusted
initially towards the transmitter delivering the intended OFDM signal. Furthermore, once the
n _{OFDM is synchronised onto the transmitter and the Node synchroniser in the Viterbi decoder has}
tio ^{locked, it is recommended to derive the quality information from the QVAL values of the Viterbi}
a ^decoder.
m _{5.3.2 Status Information of the FEC Block}
for ^{5.3.2.1 Hardware Pins}
In ^{• VLOCK (pin 142) shows the lock condition of the Node Synchroniser in the Viterbi decoder.}
Use it with caution, the VLOCK pin alone is not a reliable indication for error-free reception.
y _{• INSYNC (pin 143): H level indicates that the Frame Synchroniser after the Viterbi decoder}
r _{is in lock.}
ina ^{• TRERROR (pin 130) is the most reliable indicator for correct decoding of the MPEG-2}
transport stream. H level indicates that the RS decoder detected uncorrectable errors.
lim ^{5.3.2.2 Software Registers}
e • The QVAL registers provide information for an estimation of the channel quality. They have
r _{their roots in the FEC for the satellite system, therefore the internal calculations are}
P _{normalised to the AWGN channel. Because the conditions for terrestrial reception are}
completely different the SNR values calculated with these registers don’t reflect the real
SNR in the terrestrial transmission, nevertheless they provide useful information about the
overall channel quality.
• All the functional blocks in the FEC part can be monitored: The signals VLCK, INSYNC,
DEINT and RERRU are available as status bits.
• The BAD COUNT register contains information on erroneous transport packets in a certain
interval, its use is useful at the edges of the coverage area.
5.3.2.3 FEC Block QVAL Values corresponding to BER values
In paragraph 3.2.3.2.7 a formula is given to estimate the BER from the QVAL values. Using
Figure 3-10 and Figure 3-8 it is possible to estimate the BER from the QVAL values. In the table
below the values for the BER of 2 * 10^-4 are given for all coderates. Using these values (it is
Single Chip DVB-T Demodulator - Rev. 1.3 (11/30/98)
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