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B-38 GB1400 User Manual
Example 1
A 44.736-Mbit/s system seems to have a very low error rate; in a five-minute test no errors occurred. It is
decided to use stress to estimate the BER with no stress. When 5 dB of electrical attenuation is placed in
the signal path, 13,400 errors are measured in one second––a BER of 13400 / 44736000 = 3×10
−4
. Using
graph paper like that provided at the end of this article, plot a point at Attenuation = 5 dB and BER = 3×
10
−4
, as in Figure 6. Then the electrical attenuation is reduced to 3 dB, and 16,100 errors are measured in
60 seconds. This is a BER of 16100 / (60 × 1544000) = 6×10
−6
, which is also plotted in Figure 6. A
straight line through the two points intersects the BER axis at 10
−10
, so the unstressed BER would be 10
−
10
(one error every 3.7 minutes on average.)
10
16
10
14
10
12
10
10
10
9
10
8
10
7
10
6
10
5
BER
Attenuation (dB)
10
3
10
4
76543210
Example 1
Example 2
Figure 6. In this extrapolation, we find BER for no attenuation from BER measurements with two
attentuations. In the first example, many errors were measured, resulting in tight control of the
extrapolation. In the second, too few errors were measured, creating uncertain BER estimates
(see the bars) and a sloppy extrapolation.