Editing Bit error rate (section)

==Packet error ratio==
The '''packet error ratio''' (PER) is the number of incorrectly received [[network packet|data packet]]s divided by the total number of received packets. A packet is declared incorrect if at least one bit is erroneous. The expectation value of the PER is denoted '''packet error probability''' ''p<sub>p</sub>'', which for a data packet length of ''N'' bits can be expressed as

:<math>p_p = 1 - (1 - p_e)^N = 1 - e^{N \ln(1 - p_e)}</math>,

assuming that the bit errors are independent of each other. For small bit error probabilities and large data packets, this is approximately

:<math>p_p \approx p_eN.</math>

Similar measurements can be carried out for the transmission of [[frame (networking)|frame]]s, [[block (data storage)|block]]s, or [[symbol (data)|symbol]]s.

The above expression can be rearranged to express the corresponding BER (''p<sub>e</sub>'') as a function of the PER (''p<sub>p</sub>'') and the data packet length ''N'' in bits:

:<math>p_e = 1 - \sqrt[N]{(1 - p_p)}</math>