# 7.2 Channel coding

## Introduction

Channel coding is most often applied to communications links in order to improve the reliability of the information being transferred. By adding additional bits to the transmitted data stream (which of course increases the amount of data to be sent), it is possible to detect and even correct for errors in the receiver.

Error detection schemes – In its most elementary form this involves recognizing that part of the received information is in error and, if appropriate or possible, requesting a repeat transmission – ARQ (Automatic Repeat Request Systems). |
Error detection and correction – With added complexity, it is possible not only to detect errors, but also to build in the ability to correct errors without recourse to retransmission. This is particularly useful where there is no feedback path to the transmission source with which to request a resend. This process is known as FEC (Forward Error Correction). |