Block codes

Block codes are techniques used to transform a set of binary data "N" in another slightly longer "K" where a few extra bits are added to give redundancy to the outgoing code K, where (K>N). The number of check or redundancy digits shall be M=K-N; where M are the number of digits added.

The principle used in block codes consists of structuring the data in blocks of fixed length and adding to each block a certain number of bits called redundancy bits.

Only certain bit combinations are acceptable and form a collection of valid codewords.

When data is transmitted to the receiver, there are two possibilities:

• May the word received be a valid word of code.
• That the word received is not a valid code, in which case there are two possibilities:
  • The receiver can recreate the original FEC block (Forward Error Correction or autocorrector code).
  • The receiver may order the ARQ block to be retransmitted (Automatic Repeat reQuest or autochequeo code).