L64704 LSI Logic Corporation, L64704 Datasheet - Page 159

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

Figure 7.14
Code Word
Structure
Figure 7.15
Forward Error
Correction Data
Path
7.3.1.1 Forward Error Correction
Forward error correction requires an encoder that appends redundant
check bytes to a message before transmission. The check bytes, with an
indeterminate number of bits, are referred to as symbols. The message
symbols followed by redundant check symbols are called code words.
The check symbols are redundant in the sense that 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 7.14
A code word is a block of N bytes that includes K message symbols and
N – K check bytes (R). The check bytes or symbols are some fraction of
the message symbols. 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.
gram of the basic encoder and decoder functions in a transmission
system.
Message
After generating a code word, the encoder transmits it through a low cost
channel to a decoder. The decoder compares the bit stream in the mes-
sage data to the encoding in the check bytes to detect transmission
Reed-Solomon Decoder
Data
illustrates a code word. Explanatory text follows the figure.
Encoder
Message + Check Bytes = Code Word
K Message Bytes
Code Word – Check Bytes = Message
N Code Word Bytes
Channel
Figure 7.15
Decoder
R Redundant Check Bytes
shows a block dia-
Corrected
Message
Data
7-15