| Definition |
Decoding based on hard-bits(the output is quantized only to two levels) is called the “HD(hard-decision) decoding”, where each bit is considered definitely one or zero. |
Decoding based on soft-bits(the output is quantized to more than two levels) is called the “SD(soft-decision) decoding”, where not only one or zero decision but also confidence information for the decision are provided. |
| Application |
Generally for non-coherent detection optical systems, e.g., 10 Gbit/s, 40 Gbit/s, also for some coherent detection optical systems with higher OSNR |
coherent detection optical systems, e.g., 100 Gbit/s,400 Gbit/s. |
| Electronics Requirement |
ADC(Analogue-to-Digital Converter) is not necessary in the receiver. |
ADC is required in the receiver to provide soft information, e.g., coherent detection optical systems. |
| specification |
general FEC per [ITU-T G.975];super FEC per [ITU-T G.975.1]. |
vendor specific |
| typical scheme |
Concatenated RS/BCH |
LDPC(Low density parity check),TPC(Turbo product code) |
| complexity |
medium |
high |
| redundancy ratio |
generally 7% |
around 20% |
| NCG |
about 5.6 dB for general FEC;>8.0 dB for super FEC. |
>10.0 dB |
| Example(If you asked your friend about traffic jam status on roads and he replies) |
maybe fully jammed or free |
50-50 but I found othe way free or less traffic |
