In all types of communication systems, errors may be minimised, but they cannot be avoided completely. Hence the need for error detection and/or correction techniques. If an error is detected at the receiving end, it can be corrected in two different ways: the recipient can request a repeat of the transmission or the recipient may attempt to correct the errors without any further information from the transmitter, known as forward error correction (FEC). Retransmission is commonplace in communications system where it is possible. However, if distances are large, such as communications with a space probe, or real time signals are involved such as the case in audio and video streaming or broadcasting, retransmission is not an option.

Information messages invariably contain what is known as redundancy. In ordinary English text, the U following the Q is quite unnecessary and At this moment in time can be easily reduced to At this moment or even Now . Redundant letters or words play a very important role in communication. They allow the recipient to make sense of distorted information. This is how we can make sense of badly spelled seaside postcards, a corrupted fax message or a text message.

As far as digital communication is concerned, redundancy is unnecessary data that occupies precious bandwidth space. For this reason, compression techniques are used to ensure that only necessary data is transmitted. In video and audio processing, raw data is compressed by 100 times or more to reduce the bandwidth requirements. To provide for error...