In the error correction technique, codes are generated at the transmitter by adding a group of parity bits or check bits. The source generates the data in the form of binary symbols. The encoder accepts these bits and adds the check bits to them to produce the code words. These code words are transmitted towards the receiver. The check bits are used by the decoder to detect and correct the errors.

The encoder adds the check bits to the data bits, according to the prescribed rule. The rule will be dependent on the type of code being used. The decoder separates out the data and check bits. It uses the parity bits to detect and correct errors if they are present in the received code words. The data bits are then applied to the destination.

FEC (Forward Error Correction):

In FEC the receiver searches for the most likely correct codeword. When an error is detected, the distance between the received invalid codeword and all possible words in measured. The nearest valid codeword is the most likely correct version of the received codeword.

Some of the FEC techniques are as follows:

(i) Linear Block codes. (ii) Convolution coding. (iii) Hamming codes. (iv) Cyclic Codes.