L64777 LSI Logic Corporation, L64777 Datasheet - Page 35

• Manufacturer Part Number: L64777
• Description: DVB Qam Modulator
• Manufacturer: LSI Logic Corporation

2.7.1 Forward Error Correction (FEC)
R
d
K
m
N
t
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.”
Figure 2.13 illustrates a code word.
Figure 2.13 Code Word Structure
Reed-Solomon Encoder
K Message Bytes
Check Bytes
The encoder generates and appends check bytes to the
incoming message according to the Reed-Solomon
error-correction encoding. The decoder uses check bytes
to locate and correct errors due to transmission.
Detection Power
Detection power has a minimum value of
maximum value of R.
Message Length
The message is comprised of multiple bytes. The size of
the message varies depending on the code word length
and the check bytes used, where K = N
Symbol Size
The symbol size m is 8 bits fixed.
Code Word Length
This is the sum of the number of message bytes and the
number of check bytes (K + R).
Number of Error Corrections
This variable is the maximum number of error corrections
performed by the decoder. Its maximum value is:
N Code Word Bytes
R
--- -
2
R Redundant Check Bytes
R.
R
--- -
2
and a
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