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# WK 4 addtl info CRC - EE136 Communication Networks © Kang...

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Unformatted text preview: EE136: Communication Networks © Kang Xi, Polytechnic University Communication Networks © Kang Xi, Polytechnic Institute of NYU 11 Concept of Error Detection Code n Suppose we send out a message [1 2 5 8] and an error turns it to [ 2 2 5 8] n At the receiver, there is no way to tell whether [ 2 2 5 8] contains an error n Solution: append an error detection code to the original message at the sender EE136: Communication Networks © Kang Xi, Polytechnic University Concept of CRC n Question: what kind of error detection code to add n Assumption: sender and receiver shares a number 7 n Sender: divides the message by 7, and use the remainder as the code ¨ msg [1 2 5 8] ¨ 1258/7 = 179 + 5/7, so the reminder is 5 ¨ Now append 5 to the msg: [1 2 5 8 5 ] n When an error occurs, the receiver gets [ 2 2 5 8 5] ¨ Receiver takes [2 2 5 8] and divides it by 7 ¨ 2258/7 = 322 + 4/7, so the reminder is 4 EE136: Communication Networks © Kang Xi, Polytechnic University 22 EE136: Communication Networks...
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