L37Xrev - Error Control Basic principles for reliable...

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Error Control Basic principles for reliable communication despite errors: 1. error detection so that the chance of undetected error is negligible. 2. Use acknowledgments, and if there is any doubt that some data unit was not received correctly, retransmit it. . 3. Sequence number the data. Error detection k = number of "data" bits in the frame. c = number of checking bits. n = k+c = total frame length, not including flags. The check bits are derived from the data by a linear operation, using modulo two arithmetic. The total n bits with k data bits constitute a (n,k) block code .
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Probability and events 123 P + P + P = 1. 3, Estimate of P the probability of undetected error. For a frame of n bits, there are 2 possible received n sequences. Only 2 of these, corresponding to the k bits of data, k are actually used. - a rough estimate of the probability of undetected error.
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Error Detection and Error Correction Error detection an essential for reliable communication assurance. With no possibility of retransmission, error correction could reduce the number of incorrectly received packets. Also can provide both error correction and error detection . Increasing use of wireless links and has increased need for error correction.
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Cyclic redundancy check - feedback shift registers for encoding and error detection. Write the data sequence as K-1 K-2 0 M(X) = d X + d X ........ + d K-1 K-2 Transmission order - highest degree first. Computation of the c check bits: divide the shifted data polynomial by a c-degree binary polynomial, P(X). The remainder R(X) is a polynomial of degree < c whose coefficients are the check bits. The transmitted sequence is represented as T(X) = X M(X) + R(X) c First part is data; second part is check.
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Example: K=7, c =4.
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This note was uploaded on 09/23/2009 for the course CMPEN 362 taught by Professor Johnmetzner during the Spring '09 term at Pennsylvania State University, University Park.

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L37Xrev - Error Control Basic principles for reliable...

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