5.5 Information Coding Systems - Error Checking And Correction

Question 1

What is majority voting ?

Answer 1

An error checking method that duplicates or copies each bit in the message an odd number of times before sending these copies.

Question 2

How many bits does ASCII code become after adding a parity bit?

Answer 2

8 bits

Question 3

Where do you add a parity bit?

Answer 3

Far left

Question 4

If there are 4 ones in a ASCII code, and you are using even parity , would you add a 0 or a 1 to the ASCII code ?
Why?

Answer 4

0 ,because the number of 1s across the initially 7 bit ASCII code is already even

Question 5

Which Boolean operator can be used to work out the parity bit needed?

Answer 5

XOR (exclusive-OR)

Question 6

Explain how a receiver of data transmission consisting of one parity bit and 7 data bits can detect that an error has occurred affecting an odd number of the 8 received bits

Answer 6

Using XOR the parity bit is calculated from the data bits received. This parity bit is XORed with the parity bit received. If the result of this is a 1, then there has been an error effecting an odd number of bits.
e.g. parity bit received=1
parity bit calculated from received data=0
1 XOR 0 = 1