soft decision FEC (SD-FEC)

SD- FEC stands for Soft Decision Forward Error Correction (FEC). It is a forward error correction used in optical transmission systems such as 100 Gigabit Ethernet.

Soft decision FEC uses extra bits and its algorithm provides granular error correction. Here, the decision threshold is not taken between 1 and 0, but is based on additional intermediate levels. With this technique, SD-FEC can improve Net Coding Gain (NCG) by over one decibel compared to Enhanced FEC (E-FEC).

The >1 dB gain improvement has a direct impact on the reprocessing of the optical signals and thus on the length of the optical transmission link, and also on its economics. This is especially true for submarine cables.