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'''Turbo codes''' are a class of recently-developed high-performance [[error-correcting code|error correction codes]] finding use in deep-space [[satellite]] [[communications]] and other applications where designers seek to achieve maximal information transfer over a limited-bandwidth communication link in the presence of data-corrupting noise.
=== The Shannon Limit ===
The method was introduced by [[Claude Berrou|Berrou]], [[Alain Glavieux|Glavieux]], and [[Punya Thitimajshima|Thitimajshima]] in their [[1993]] paper: "''Near Shannon Limit error-correcting coding and decoding: Turbo-codes''" published in the Proceedings of IEEE International Communications Conference [http://www-elec.enst-bretagne.fr/equipe/berrou/Near%20Shannon%20Limit%20Error.pdf]. Turbo code refinements and implementation are an area of active research at a number of universities.▼
Of all practical error correction methods known to date, turbo codes, together with [[Low-density parity-check code]]s, come closest to approaching the [[Shannon limit]], the theoretical limit of maximum information transfer rate over a noisy channel.
Turbo codes make it possible to increase available bandwidth without increasing the power of a transmission, or they can be used to decrease the amount of power used to transmit at a certain data rate. Its main drawbacks are the relative high decoding complexity and a relatively high [[latency (engineering)|latency]], which makes it unsuitable for some applications.
* For satellite use, this is not of great concern, since the transmission distance itself introduces latency due to the limited [[speed of light]]. Turbo codes are used extensively in [[3G]] mobile telephony standards. Prior to Turbo codes, the best known technique combined a [[Reed-Solomon error correction]] [[block code]] with a [[Viterbi algorithm]] [[convolutional code]].
===
▲The method was introduced by [[Claude Berrou|Berrou]], [[Alain Glavieux|Glavieux]], and [[Punya Thitimajshima|Thitimajshima]] in their [[1993]] paper: "''Near Shannon Limit error-correcting coding and decoding: Turbo-codes''" published in the Proceedings of IEEE International Communications Conference [http://www-elec.enst-bretagne.fr/equipe/berrou/Near%20Shannon%20Limit%20Error.pdf]. Turbo code refinements and implementation are an area of active research at a number of universities.
There are two related features of turbo codes that make them different from the more traditional error-correcting codes of the 20th century: ▼
===How turbo codes work===
▲There are two related features of turbo codes that make them different from the more traditional error-correcting codes of the 20th century
* The key insight is the realization that instead of producing a stream of binary digits from the signal it receives, the front-end of the decoder can be designed to produce a likelihood measure for each bit.
* The nitty-gritty of turbo codes is the design of the decoder (and the coder) so that it can exploit this additional information.
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