BER (with No FEC) vs Pre-FEC BER vs Post FEC BER

[krishna G]

Hi,

Can you please explain the difference between BER (with No-FEC) , PRE-FEC BER and Post-FEC BER??

As per my understanding , PRE-FEC BER is the BER at the I/p of the FEC Decoder and Post FEC BER is the BER at the o/p of FEC Decoder. But when I saw the graph of BER vs OSNR , I see curves for No-FEC,PRE-FEC,POST-FEC and asymptotic..

Can you explain the difference elaborately.

Regards
Krishna

[Huub van Helvoort]

Hello Krishna,

PRE-FEC BER are the bit errors caused by attenuation, ageing,
temperature changes of the optical fiber.
PRE-FEC indicates that the signal on the optical fiber is FEC
encoded.
The FEC decoder will recover the original signal, but depending
on the PRE_FEC BER it will succeed to recover the original signal
completely without errors.
Or, if the BER on the fiber is too high, the recovered signal will
contain bit errors.
If the signal was FEC encoded the remaining bit errors after the
decoder are called POST_FEC BER.

The NO_FEC BER are the bit errors detected when no FEC coding is
used on the optical fiber.

See also: https://goo.gl/cuhbjj

Best regards, Huub.




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[Ramakrishna Pratapa]

Just wanted to add a point here on the asymptotic nature of the curves:

As the OSNR reduces, the BER increases and FEC facilitates error correction depending on the coding gain the FEC algorithm can provide. Beyond the FEC limits, even minor OSNR degradation could mean significant performance loss which is seen in the asymptotic nature of the curve.