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Error detection and correction

A simple presentation of error detection and correction in data communication.

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Error detection and correction

  1. 1. Error Detection and Correction
  2. 2. Presented By:Maria AktherDept.: Computer ScienceDaffodil International University
  3. 3. Data can be corrupted during transmission.some applications require that errors be detectedand corrected.
  4. 4. 1.Single-Bit Error2.Burst Error
  5. 5. In a single-bit error only 1 bit in the data unit has changed.Example:The effect of a single-bit error on a data unit in shown fig.The impact of the change, imagine that each group of 8bit is an ASCII character with a 0 bit added to the left. In fig.00000010 was sent ,meaning start of text,but 00001010 was received, meaning line feed.
  6. 6. A burst error means that 2 or more bits in the data unit havechanged.Example:The effect of a burst error on a data unit.In thiscase,0100010001000011 was sent,but 0101110101100011 wasreceived.the length of the burst is measured from the firstcorrupted bit to the last corrupted bits
  7. 7. The central concept in detecting or correcting errorsis redundancy. To be able to detect or correct errors,we need to send some extra bits with our data.These redundant bits are added by the sender andremoved by the receiver. Their presence allows thereceiver to detect or correct corrupted bits.
  8. 8. DetectionIn error detection, we are looking only if any error has occurred. A single bit error is the same for us as a burst error.CorrectionIn correction, we need to know the exact number of bits that are corrupted and their location in the message. The number of the errors and size of message are important.
  9. 9.  Forward error correction Retransmission
  10. 10.  Block coding Convolution coding
  11. 11. In block coding, we divide our message into blocks,each of k bits, called datawords. We add r redundantbits to each block to make the length n = k + r. Theresulting n-bit blocks are called codewords.
  12. 12. Two conditions are met to detect an error by thereceiver-2.The receiver has a list of valid codewords.3.The original codeword has changed to an invalidone.
  13. 13. The sender encodes the dataword 01 as 011 and sends it to the receiver. The receiver receives 011. The receiver receives 111.
  14. 14. Assume the sender creates dataword 01 as01011.The codeword is corrupted duringtransmission and 01001 is received.
  15. 15. • The Hamming distance between two words is the number of differences between corresponding bits.• Hamming distance between two words x and y can be shown as d(x, y)
  16. 16. 1. The Hamming distance d(000, 011) is 22. The Hamming distance d(10101, 11110) is 3