Digital signals use FEC in these three well known methods:

Forward Error Correction
When a duplex line is not available or is not practical, a form of error correction called Forward Error
Coding (FEC) is used. The receiver has no real-time contact with the transmitter and can not verify if a block
was received correctly. It must make a decision about the received data and do whatever it can to either fix it or
declare an alarm.
FEC techniques add a heavy burden on the link either in adding redundant data and adding delay. Also
most FEC techniques are not very responsive to the actual environment and the overhead is there whether
needed or not. Another big disadvantage is the lower information rate. However at the same time, these techniques
reduce the need to vary power. For the same power, we can now achieve a lower error rate. The communication
in this case remains simplex and all the burden of detecting and correcting errors falls on the receiver.
The transmitter complexity is avoided but is now placed on the receiver instead.
Digital signals use FEC in these three well known methods:
1. Block Codes
2. Convolutional Codes
3. Interleaving