PRESENTATION ON CYCLIC REDUNDANCY CHECK(CRC)

PRESENTED BY-

SUDHANSHU SRIVASTAVA(210001)

ABHISHEK SINGH(210002)

SAURABH PRATAP SINGH(210003)

ASHUTOSH KUMAR CHATURVEDI(210005)

CONTENT

1. ERROR DETECTION

2.ERROR CORRECTION

3.CYCLIC REDUNDANCY CHECK(CRC)

4.CRC POLYNOMIAL

5.ADVANTAGE OF CYCLIC CODES

ERROR DETECTION

Error detection is the detection of errors caused by noise or other impairments during transmission from the transmitter to the receiver. Summer is another name for error detection.

The receiver can detect a change in the original code word.

• 1. The receiver has (or can find) a list of valid code words.

• 2. The original code word has changed to an invalid one.

PROCESS OF ERROR DETECTION

ERROR CORRECTION

• Error correction is the detection of errors and reconstruction of the original, error-free data.

• error correction is much more difficult than error detection. In error detection, the receiver needs to know only that the received code word is invalid.

• In error correction the receiver needs to find (or guess) the original code word sent.

• we need more redundant bits for error correction than for error detection.

STRUCTURE OF ENCODER & DECODER IN ERROR CORRECTION

CYCLIC REDUNDANCY CHECK (CRC)

• Cyclic codes are special linear block codes with one extra property. In a cyclic code, if a code word is cyclically shifted (rotated), the result is another code word.

• A cyclic redundancy check (CRC) is an error-detecting code commonly used in digital networks and storage devices to detect accidental changes to raw data.

• Blocks of data entering these systems get a short check value attached, based on the remainder of a polynomial division of their contents; on retrieval the calculation is repeated, and corrective action can be taken against presumed data corruption if the check values do not match.

A CRC code with C(7,4)

CRC encoder and decoder

DIVISION IN CRC ENCODER

DIVISION IN CRC DECODER

USING POLYNOMIAL

• We can use a polynomial to represent a binary word.

• Each bit from right to left is mapped onto a power term.

• The rightmost bit represents the “0” power term. The bit next to it the “1” power term, etc.

• If the bit is of value zero, the power term is deleted from the expression.

CRC DIVISION USING POLYNOMIALS

ADVANTAGES OF CYCLIC CODES

• Cyclic codes have a very good performance in detecting single-bit errors, double errors, an odd number of errors.

• They can easily be implemented in hardware and software.

• They are especially fast when implemented in hardware.

• This has made cyclic codes a good candidate for many networks.

THANKING YOU…