18-03-2011, 06:29 PM
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 | M.Arsalan Qureshi | | Join Date: Oct 2008 Location: Garden Town, Multan Cantt
Posts: 616
Program / Discipline: BSTS Class Roll Number: 09-31 | |
 Error Detection and Correction
Error Detection and Correction
* Errors can be categorized as a single-bit error or a burst error. A single-bit error has one bit error per data unit. A burst error has two or more bit errors per data unit. * Redundancy is the concept of sending extra bits for use in error detection. * Three common redundancy methods are parity check, cyclic redundancy check (CRC), and checksum. * An extra bit (parity bit) is added to the data unit in the parity check. * The parity check can detect only an odd number of errors; it cannot detect an even number of errors. * In the two-dimensional parity check, a redundant data unit follows n data units. * CRC, a powerful redundancy checking technique, appends a sequence of redundant bits derived from binary division to the data unit. * The divisor in the CRC generator is often represented as an algebraic poly-nomial. * Errors are corrected through retransmission and by forward error correction. * The Hamming code is an error correction method using redundant bits. The number of bits is a function of the length of the data bits. * In the Hamming code, for a data unit of m bits, use the formula 2 r >= m +r +1 to determine r, the number of redundant bits needed. * By rearranging the order of bit transmission of the data units, the Hamming code can correct burst errors.
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