Tektronix 071-0590-00 user manual Ber

BERT Technical Articles

(µ − σ) / T < r' < (µ + σ) / T

or

r − r / T < r ' < r + r / T .

These two "bounds" are shown by the two curves in Figure S-2. The measured error rate r' is seen to lie between them most of the time. As T increases, the bounds get closer to r = 5 / hr, but there will always be some deviation of r' from r. Therefore the "actual" error rate r can never be known in practice; it would take an infinite time to measure r.

The standard deviation of the error measurement n is σ = μ = rT . But since µ and r can't be known exactly in practice, we must use the estimates µ ≈ n and r ≈ r' to get the estimate

σ ≈	n =	r ' T .
102
10 3
10 4
105
BER
10 6
10 7
10 8
10 9
10 10
1012
10 14
10 16	1	2	3	4	5	6	7	8	9	10	11 (elec)
0
0	0.5	1	1.5	2	2.5	3	3.5	4	4.5	5	5.5(opt)

Attenuation (dB)

Figure S-2.Specially distorted scale so plots of BER versus signal Attenuation (electrical or optical) are straight lines (parallel to the dashed lines) when the noise is Gaussian.

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GB1400 User Manual B-43