L64704 LSI Logic Corporation, L64704 Datasheet - Page 142

• Manufacturer Part Number: L64704
• Description: Satellite Decoder Technical Manual 5/97
• Manufacturer: LSI Logic Corporation

6.4
Descrambler
Synchronization
Figure 6.10
Descrambler
Synchronization
6-10
In addition to providing the proper data alignment for the following
Deinterleaver and Reed-Solomon Decoder modules, the second
synchronization stage resolves the 180-degrees phase uncertainty that
the upstream demodulator may have introduced. The first (Viterbi)
synchronization stage is not able to detect this source of error. During
the acquisition phase, the decoder simultaneously looks for the synchro-
nization word and its complemented version to resolve the uncertainty.
The decoder does not remove the sync byte from the data stream
because it is part of the MPEG system layer syntax, and therefore the
channel decoding operation leaves it undisturbed.
This section describes the third stage synchronization; Descrambler
synchronization.
process.
The L64704 restarts the Descrambler every 8 N byte times. The L64704
aligns this restart with the complemented synchronization word that is
present in the data stream once every eight Reed-Solomon code words
(once every 8 N bytes).
Configuration Parameters
For this third stage synchronization, the L64704 uses an approach very
similar to that used in the second synchronization stage during the acqui-
sition phase to ensure proper data alignment. Because the detection of
an out-of-synchronization condition in the second stage automatically
Decoding Pipeline Synchronization
Sync Word
M, N, L, K,
MC,
LSC
Data Stream
Figure 6.10
illustrates the Descrambler synchronization
Bit Stream
Monitor
Decision Logic
Descrambler
Module
Sync Strobes