Tektronix RFA300A, User Manual

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Reference
3- 16
RFA300A Measurement Set 8VSB
Supplementary sync signals are added to a multiplexer to form the 8VSB
baseband signal. Each of the eight levels represents a symbol value. After every
828 symbols, a Segment sync is sent. The Segment sync is two-level binary data
that is 10 constellation units peak-to-peak in amplitude and four symbols long.
This makes each 8VSB data segment 832 symbols long as shown in Fig-
ure 3--16. The Segment sync has two roles: it replaces the sync byte that was
removed before the RS encoding, and it increases the signal robustness. It is
easily located by the receiver’s decoder in the presence of noise.
Data + FEC
Data
segment
sync
Levels
before
pilot
insertion
828 Symbols = 187 data bytes + 20 parity (R-S) bytes
4
Symbols
1 byte
+7
+5
+3
+1
-1
-5
-7
-3
Data
segment
sync
4
Symbols
1 byte
832 Symbols = 188 byte MPEG data 20 parity bytes
Figure 3- 16: Data segment sync
Multiplexer