MC92314 Datasheet, PDF (36/100 Pages) Motorola, Inc – DVB-T Single Chip Demodulator Application Note

Device Description
Freescale Semiconductor, Inc.
code rates and channel SNR. It shows the probability that the estimate from the graph is within
+/- 0.1 dB of the actual channel SNR.
Table 3-6. Probability Of p₀ Accuracy
AVRG_PERIOD
1
2
4
8 (default)
15
# Of Samples
32768
65536
131072
262144
491520
Probability Of +/- 0.1dB Accuracy
r=1/2, E_b/N₀=1.2
0.541559
r=7/8, E_b/N₀=3.5
0.999799
0.700163
1
0.855141
1
0.960214
1
0.995069
1
From the table it can be seen that even using the default value for AVRG_PERIOD the probability
n that the p₀ estimate of SNR is within 0.1 dB is 96% (even for small SNR values). For increased
tio ^{AVRG_PERIOD values or increased SNR values the probability is 100% for all practical}
purposes.
a _{3.2.3.3 Frame Synchronisation}
rm _{3.2.3.3.1 MPEG Frame Synchroniser and Deinterleaver}
fo This section of the manual describes the Frontend of the Reed-Solomon decoder in the
In ^{MC92314. The data received from the Viterbi decoder is internally a continuous stream of bits}
and must be segmented into blocks (MPEG-2 Transport Packets) and subsequently into bytes
y that the Reed-Solomon can manipulate. The Frame Synchroniser recognizes the
r _{Synchronisation Bytes (Sync Bytes) embedded in the data stream and communicates these as}
a _{frame boundaries to the Reed-Solomon decoder and the other functional blocks. The 12x17}
in ^{Forney Deinterleaver processes the input bit stream to break up and distribute the longer burst}
errors throughout the MPEG-2 packet.
lim _{3.2.3.3.2 Frame Structure and Synchronisation Scheme}
re The MPEG-2 Transport Packet consists of one leading Sync Byte (0x47), 187 information bytes
P ^{and 16 Reed-Solomon Check Bytes (for a total of 204). In addition, the Sync Byte of every eighth}
packet is inverted from 0x47 to 0xB8. The frame structure of the interleaved data is depicted in
Figure 3-11. The synchroniser uses this structure to determine the byte and frame boundaries to
synchronise the deinterleaver and the decoder and also to resolve the π-ambiguity of the data
within the input stream.
MOTOROLA
3-18
Single Chip DVB-T Demodulator - Rev. 1.3 (11/30/98)
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