Error Correction

Parity Checks

One method of error checking would be parity bits which appends a 1 or 0 to the end of 7 bit packet. This additional bit is for even parity and odd parity error checking.

Even parity

Even parity will check to see if there is an even number of 1's in the first 7 bit of the packet. If there is an even amount, there would be a number 1 appended to the packet, otherwise 0 would be appended to the end of the packet. If there would have been an error in the transmission, the receiving party would receive the packet with either an even number of 1's in the packet but "0" parity bit at the end of the packet or an odd number of 1's in the packet but a "1" party bit.

Odd parity

Odd parity will check to see if there is an odd number of 1's in the first 7 bit of the packet. If there is an even amount, there would be a number 0 appended to the end of the packet, otherwise 1 would be appended. If an error occurred in the transmission, the receiving party would receive the packet with either an even number of 1's in the packet but "1" parity bit at the end of the packet or an odd number of 1's in the packet but a "0" party bit.

However, if there were 2 bits that were transmitted with errors, then the check would not find the errors and it will be sent regardless, causing the parity check to not work.

Majority Voting

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Majority voting sends the same bit 3 times and goes with the most common bit for example instead of sending a 1 it would send 1 1 1 and if there was an error it would be 1 1 0 but as there are 2 ones That is what will be used.

Sending 0110 would be sent 000 111 111 000. This means if an error occurs it wont change the data as an error in 0110 might be 1110, Which would be completely different however if an error occurs in 000 111 111 000 It might be 010 111 110 000 But the data wouldn't be different as it would still be read as 0110.

If 2 error occurs in the same 3 bits the majority will be the wrong bit also changing it completely so 010 should be 000 111 000 But if it was 011 111 000 it would be read as 110. This is a downside to majority voting.

Check Sums

A check sum is another form of error correction. Check sums uses maths to check by counting or algorithms.