method of error detection for digital signals

why CRC ? CRC vs parity ?

A parity bit check detects only single bit errors

CRC error correction allows detection of:

1. single bit errors
2. double bit errors
3. bundled bit errors (bits next to each other)

Some popular techniques for error detection are:

1. Simple Parity check (even parity ==> if msg has odd no. of 1's add extra 1 to make it even parity & at Rx end check for even no. of 1's)

2. Two-dimensional Parity check ( divide msg into colums and parity check each column)

3. Checksum (divide msg into 8/16..etc bit parts & add all 8/16..etc bits and compliment final sum to get check-sum at receiving end also cal sum & add check-sum if all bits are 1,s ==> no error)

4. Cyclic redundancy check (Refer Below) Tx(Mtx) ------------------------------------------> Rx(Mrx) if Mtx == Mrx No error transmission; else error in transmission.

   Example: Mtx = base2(110101) = base10(53) let divisor = base10(5) = base2(101) = d Mtx/d = 53/5 = 3 = base2(11) Message with CRC = base2(110101) + base2(11) = base2(11010111) = base10(215) mrx = 215 error check: 215/5 = 0 ==> No error

References https://www.geeksforgeeks.org/error-detection-computer-networks/ http://ww1.microchip.com/downloads/en/AppNotes/00730a.pdf