L64777 A LSI Logic Corporation, L64777 A Datasheet - Page 12

• Manufacturer Part Number: L64777 A
• Description: Communications, DVB QAM Modulator
• Manufacturer: LSI Logic Corporation

Energy Dispersal (Scrambler) Unit
Reed-Solomon Encoder
Forward Error Correction (FEC)
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The function of the Scrambler is specified for the serial domain by the
Digital Broadcasting Systems for Television Sound and Data Services:
Framing Structure, Channel Coding and Modulation Cable Systems . The
energy dispersal module (scrambler) operates in Parallel mode based on
the algorithm of the serial domain.
The scrambler block consists of two major modules: one to generate a
pseudo-random binary sequence (PRBS) that modifies the incoming
data stream, and the other a control module that properly aligns data
with the PRBS.
Reed-Solomon (RS) error correction codes are systematic and operate
on bytes rather than single-bit data streams. The codes are expressed
by convention as two numbers, the first indicating the total code word
length (N), and the second indicating the number of message bytes (K).
The difference between these two numbers (N
check bytes.
The error-correcting power of an RS code is related to the number of
redundant check symbols in its code words. In general, an RS code with
2t check symbols per code word can correct up to “t” byte errors per
code word. Higher redundancy allows more errors to be corrected.
FEC requires an encoder that appends redundant check information to
the message before transmission. The bytes with an indeterminate
number of bits are referred to as symbols. The message symbols and
following redundant check symbols make up code words. The check
symbols are redundant because they are derived from the message and
are appended to the message. Check symbols are also referred to as
“redundant check bytes,” and sometimes as “correction bytes.”
A large number of check symbols allows the decoder to correct a large
number of transmission errors. The redundant check symbols in a
message allow a decoder at the receiving end of a transmission line to
detect transmission errors and reconstruct the original message content.
L64777 DVB QAM Modulator
K) is the number of