Instrument Function
R&S
®
SMBV100A
186
Operating Manual 1176.8016.02 ─ 17
The BER/BLER measurement measures statistical bit/block errors, i.e. errors which do
not occur at regular intervals, but at random. Although a single measurement deter-
mines the exact number of errors in the measured interval, you can only obtain a stat-
istically reliable BER/BLER when a sufficient number of errors occur in the measured
interval. This way makes sure that the single BER/BLER measurement result
approaches the true error rate with high probability.
Bit error rates of approximately 50
% indicate a faulty measurement.
5.4.6 Interrupt-free Measurement
In the case of continuously generated signals that contain whole-number multiples of
the PRBS sequence, the measurement occurs without interruption. Only the data and
clock lines of the BERT interface are used for the measurement. The length of the ran-
dom sequence is 2 to the power of the degree of the polynomial minus 1. For example,
PRBS9 length of 511 (2
9
equals 512 minus 1).
5.4.7 Restart Function
The "Restart" function allows BER measurements with short signals or with signals that
are not continuously generated (and therefore do not contain any whole-number multi-
ples of PRBS sequences). An external signal at the BERT input halts the measurement
and restarts it when the data sequence begins, and the BER results of the relevant
(sub)sequences are integrated.
Figure 5-2: The length of the signal is too short for a complete PRBS sequence; PRBS generation is
restarted by the Restart signal when the signal begins anew.
Frames generated by the R&S
SMBV or the R&S WinIQSIM2 software contain contin-
uous PRBS data, i.e. the PRBS sequence is continuously written to the user data
fields. Consequently, if the R&S
SMBV is used as a data source, a restart is necessary
if (e.g. when using a waveform) the total length of the signal does not equal a whole-
number multiple of a PRBS sequence.
Bit and Block Error Rate Measurements
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