Instrument Function
R&S
®
SMU200A
177Operating Manual 1007.9845.32 ─ 15
5.4.5 Ending the measurement
The measurement results usually lie in the range of 10-2 to 10-9 for the bit error rate, and
in the range of 10
-2
to 10
-4
for the block error rate. This means that a very large number
of bits or blocks may have to be tested before a faulty bit or block occurs. Because of the
large number of bits/blocks involved, the measurement time is usually very long. Since
32-bit-wide counters are used for the total number of bits/blocks and the number of error
bits, the maximum measurement time is 4.29 x 10
9
bits.
To keep the measurement times short for both small and large bit/block error rates, the
R&S Signal Generator provides a number of ways to end the measurement. In addition
to manually interrupting the count, two termination criteria can be selected:
1. reaching a user-defined number of checked data bits/blocks;
2. a maximum number of detected errors.
The measurement stops as soon as one of the two criteria has been met. The display
shows which of the two criteria caused the measurement to stop.
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 determines
the exact number of errors in the measured interval, a statistically reliable BER/BLER
can only be obtained when a sufficient number of errors occur in the observed interval.
This is the only way to ensure 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 random
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 makes it possible to perform BER measurements with short signals
or with signals that are not continuously generated (and therefore do not contain any
whole-number multiples 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.
Bit and Block Error Rate Measurements - BERT Block
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