The signals that are received at the end users' site are often erroneous, particularly in the wireless environment, due to noise and multi-path interference in the transmission medium, among other things. These errors are experienced by the end-user as signal degradations, and consequently degradation of the quality of service. In the two-way communication networks, the problem of errors is often solved by retransmission of the signal. Another technology that can be used, when there is no return path to send commands up-stream and ask the source to retransmit the signal, or the timing requirements of the signal does not permit retransmission, is Forward Error Correction (FEC).
FEC is implemented so that some overhead information is calculated and added to the signal prior to transmission. The FEC overhead information is then used in the decoder to detect and, if possible, correct the errors in the signal. An important issue regarding FEC is that a part of the transmission capacity is ‘sacrificed’ to reduce errors and increase quality, and the greater the capacity that is ‘sacrificed’ for the FEC overhead, the more secure the transmission. In practice, the level of FEC is determined by the characteristic of the transmission medium.