Operating Manual Vol 1 - ES Documentation

Bit Error Rate TestSMIQPN generator N a1 a2 a3 Output Acc. to standardPN9 9 4 - - non-inverted ITU-T Rec. O.153 Fascicle IV.4PN11 11 2 - - non-inverted ITU-T Rec. O.152 Fascicle IV.4PN15 15 1 - - inverted ITU-T Rec. O.151 Fascicle IV.4PN16 16 5 3 2 non-inverted --PN20 20 3 - - non-inverted ITU-T Rec. O.153 Fascicle IV.4PN21 21 2 - - non-inverted --PN23 23 5 - - inverted ITU-T Rec. O.151 Fascicle IV.4Measurement Result, Accuracy, Measurement TimeValue rangeStatisticsTerminationcriteriaInterruption ofmeasurementMeasurement results for the bit error rate (ie the quotient of error bits and totalbits) are usually found between 10 -2 and 10 -9 . This means that a large number ofbits may have to be checked before a faulty bit is detected. Because of the largenumber of bits involved the measurement time is usually very long.Since 32-bit-wide counters are used for the total bits and the error bits, themaximum measurement time is 4.29 x 10 9 bits.The BER measurement measures statistical bit errors, ie errors which do notoccur at regular intervals but at random. Although a single measurementdetermines the exact number of errors in the measured interval, a statisticallyreliable BER can only be obtained when a sufficient number of errors occurs in theobserved interval. Only this ensures that the single BER measurement resultapproaches the true error rate with high probability .To keep the measurement time short with low and high bit error rates, twotermination criteria have been defined in the SMIQ for the BER measurement.• Criterion 1: Total number of bitsThe measurement is terminated when the specific number of data bits isreached. Due to this criterion the BER measurement is reliably stopped afterthe specified number of bits even if no error or only a few errors were detected;the measurement result is not statistically reliable (few bit errors).• Criterion 2: Number of errorsThe measurement is terminated when the specified number of bit errors isdetected. With this criterion, the measurement is rapidly terminated when highbit error rates occur. Since a great number of errors is counted, themeasurement result is statistically reliable.The two criteria are used together. The criterion which finally yields a valid result isindicated in the results screen ("Measurement terminated by...").At the end of a measurement, the restart of a new one is delayed until the firstmeasurement result has been queried with :BERT:RES?. The resulting briefmeasurement interruption is irrelevant because the subsequent measurement willbe synchronized within 24 data bits.1125.5555.03 2.376 E-9