In digital telecommunications, channel coding is a pre-transmission mapping applied to a digital signal or data file, usually designed to make error-correction possible.
Error correction is implemented by using more digits (bits in case of a binary channel) than the number strictly necessary for the samples, and having the receiver compute the most likely valid message that could have resulted in the received one.
Channel coding should not be confused with source coding, which is the elimination of redundancy in order to make efficient use of storage space and/or transmission channels.
Channel coding should also not be confused by line coding, which is the coding performed in order to adapt the transmitted signal to the (electrical) characteristics of a transmission channel.
In a common communication system, at the transmitting point there is first source coding, then channel coding, then line coding.
Types of channel coding include:
Examples of source coding are:
Examples of line coding include: B8ZS, HDB3, 2B1Q, AMI and Gray coding