ENC3250 Solutions pg 34

ENC3250 Solutions pg 34 - CHAPTER 8 CODING AND ERROR...

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Unformatted text preview: CHAPTER 8 CODING AND ERROR CONTROL A N SWERS NSWERS TO Q UESTIONS 8.1 A parity bit appended to an array of binary digits to make the sum of all the binary digits, including the parity bit, always odd (odd parity) or always even (even parity). 8.2 The CRC is an error detecting code in which the code is the remainder resulting from dividing the bits to be checked by a predetermined binary number. 8.3 The CRC has more bits and therefore provides more redundancy. That is, it provides more information that can be used to detect errors. 8.4 Modulo 2 arithmetic, polynomials, and digital logic. 8.5 It is possible. You could design a code in which all codewords are at least a distance of 3 from all other codewords, allowing all single-bit errors to be corrected. Suppose that some but not all codewords in this code are at least a distance of 5 from all other codewords. Then for those particular codewords, but not the others, a doublebit error could be corrected. 8.6 An (n, k) block code encodes k data bits into n-bit codewords. 8.7 An (n, k, K) code processes input data k bits at a time and produces an output of n bits for each incoming k bits. The current output of n bits is a function of the last K × k input bits. 8.8 A trellis is a diagram that shows the state transitions over time in a convolutional code. 8.9 Detection of errors and retransmission of frames that are received in error. 8.10 Go-back-N ARQ is a form of error control in which a destination station sends a negative acknowledgment (NAK) when it receives an error. The source station receiving the NAK will retransmit the frame in error plus all succeeding frames transmitted in the interim. A N SWERS NSWERS TO PROBLEMS 8.1 Any arithmetic scheme will work if applied in exactly the same way to the forward and reverse process. The modulo 2 scheme is easy to implement in circuitry. It also yields a remainder one bit smaller than binary arithmetic. 8.2 a. We have: Pr [single bit in error] = 10–3 -34- ...
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This note was uploaded on 02/20/2012 for the course ENC 3250 taught by Professor Dr.timothycerner during the Fall '11 term at UNF.

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