When data is transmitted to its destination over a communication channel there is a possibility of errors being introduced into the the data. In digital communication performance of the system is assessed by a term called as bit error rate, BER. BER is also known by the term Probability of Error.
In simple words, it is actually the ratio of number of bits in error to the total number of bits transmitted.
BER = Bits in Error/Total Number of Bit transmitted
For instance, If 10 bits were transmitted, and 5 bits get in error,then :
In BER curve if a value is mentioned, say 0.01, it means ,out of 100 transmitted bits, 1 bit got error [1/100=0.01]
Let's consider an example, assume a transmitted bit sequence:
0 1 1 0 0 0 1 0 1 1
and the following received bit sequence:
0 0 1 0 1 0 1 0 0 1,
The number of bit errors (the underlined bits) is in this case 3. The BER is 3 incorrect bits divided by 10 transmittedbits, resulting in a BER of 0.3 or 30%.