In digital transmission, the number of bit errors is the number of received bits of a data stream over a communication channel that have been altered due to noise, interference, distortion or bit synchronization errors. The bit error rate (BER) is the number of bit errors per unit time. The bit error ratio (also BER) is the number of bit errors divided by the total number of transferred bits during a studied tim. ExampleAs an example, assume this transmitted bit sequence: 1 1 0 0 0 1 0 1 1 and the following. 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. In a communication system, the receiver side BER may be affected by transmission channel,,, problems,, wireless , etc. The BER m. The BER may be evaluated using stochastic () computer simulations. If a simple transmission and model is assumed, the BER may also be calculated analytically. BERT or bit error rate test is a testing method for that uses predetermined stress patterns consisting of a sequence of logical ones and zeros generated by a test pattern generator.