Encoder and Decoder

Díaz Nafría, José María jnafria@uax.es
 Incorporated contributions
Díaz (09/01/09)
 Usage domain
transdisciplinary, communication theory, telecommunication
codificateur / decodificateur
 German Kodierer / Dekodierer
Encoder is a device for converting data or signals by using a specific code. It is normally used with four clearly differentiated purposes: 
1) To remove redundancy or anything that is not going to be perceived by the information receiver or remain beyond the quality goals of the received signal, typically named source encoder
2) To increase redundancy, so that the decoder can eventually detect and correct the errors occurred within the reception of signals or symbols, named channel encoder
3) To make the coded data unreadable, except if the recipient knows the code, by using encryptors or ciphers
4) To allow the transmission of data through a channel with certain resources and limitations, corresponding in the MTC communication model to the transmitter-encoder, also named modulator -especially in telecommunications-.

The decoder (E. decodificador, F. decodificateur, G. Dekodierer) is the device performing the inverse operation of the encoder, whatever the purpose of the code: 1) the source decoder tries to restore the eliminated redundancy; 2) the channel decoder removes the redundancy that has been introduced by the corresponding encoder, and correct those errors being detected; 3) the unencryptor makes the data readable; and 4) the demodulator or receiver-decoder identifies the symbol transmitted through the channel –normally according to a maximum likelihood criterion– and restate the data into its original form, i.e., how it was before the modulator.
  • SHANNON, C. E. (1948). “A Mathematical Theory of Communication”. The Bell System Technical Journal, Vol. 27, pp. 379–423, 623–656, July, October, 1948.
  • SHANNON, C. y WEAVER, W. (1949). The mathematical theory of communication. Urbana: The University of Illinois Press, 1949.
  • SKLAR, Bernard (2001) Digital Communications. Fundamentals and Applications. New Jersey: Prentice Hall.
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Díaz Nafría (09/01/2009)
{It corresponds with the preliminary version which is reproduced in the left column}