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Syllabus: Fundamentals of error correction, Hamming codes, CRC.
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Linear block codes and minimum distance
Everything about detection and correction capability follows from , which for a linear code equals the smallest Hamming weight among its non-zero codewords — so you never have to compare all pairs.
linear codes only
generator and parity-check matrices; a zero syndrome means no detected error
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Hamming codes and CRC
A Hamming code is the single-error-correcting code with the fewest parity bits: parity bits address positions, so
condition for single-error correction
standard Hamming codes, all with
one extra overall parity bit
remainder of a modulo-2 division; appended as the check bits
which is why it is used on every practical link
Where marks are lost
CRC arithmetic is modulo 2 — subtraction is XOR, with no borrows. Doing the long division with ordinary binary subtraction gives a wrong remainder every time.
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