The bit error ratio (also BER) is the number of bit errors divided by the total number of transferred bits during a studied time interval. Bit error ratio is a unitless performance measure, often expressed as a percentage.OverviewIn, the number of bit errors is the number of received of a over a that. As an example, assume this transmitted bit sequence: 1 1 0 0 0 1 0 1 1 and the following received bit sequence: 0 1 0 1 0 1 0 0 1, The numbe. The packet error ratio (PER) is the number of incorrectly received 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.