## Pre-FEC BER corresponding to Q.

- BER and Q can be calculated from one another according to the following relationship:

- Or, in Excel: dBQ = 20*LOG10(-NORMSINV(BER))
- dBQ = 20Log(Q)

## Post-FEC BER/Q

- Post-FEC BER of <1e-15 essentially means no post-FEC errors
- This is equivalent to ~18dBQ, which is about as high as can be measured

## FEC Limit

- This is the lowest Q (or highest BER) that can be corrected by the FEC
- Beyond this post-FEC errors will occur

e.g

FEC Limit: 8.53dBQ or a BER of 3.8e-3

FEC Limit: 5.23dBQ or a BER of 3.4e-2 (<97% of bits have to be correct!)

### Pre-FEC Calculation eg.

Assume: 219499456 : Bit Errors 0 : Uncorrectable words 6.4577198E-6 : PRE-FEC BER Assume the Time at this instant of performance was 12:05:04 which means : 304 Seconds since the last time interval. |
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Assume The FEC settings was : STANDARD FEC so the Rate used for 100 G transponder is : 1.1181 * 10^11 |
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General Formula to calculate PRE_FEC: | ||||||

PRE_FEC BER = TotalErrors |
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So Substituting the Values | ||||||

219499456 / (304*1.1181 * 10^11) = 6.4577198E-6 | ||||||