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==Applications==
Concatenated codes were first implemented for [[deep space]] communication in the [[Voyager program]], afterwhich the craft had finishedlaunched their encounters with thefirst outerprobe Gasin Giants1977.<ref name="deep-space-codes">K. Andrews et al., ''The Development of Turbo and LDPC Codes for Deep-Space Applications'', Proceedings of the IEEE, Vol. 95, No. 11, Nov. 2007.</ref> Since then, concatenated codes became the workhorse for efficient error correction coding, and stayed so at least until the invention of [[turbo codes]] and [[LDPC codes]].
Typically, the inner code is not a block code but a soft-decision [[convolutional code|convolutional]] [[Viterbi decoder|Viterbi-decoded]] code with a short constraint length. For the outer code, a longer hard-decision block code, frequently [[Reed Solomon]] with 8-bit symbols, is selected . The larger symbol size makes the outer code more robust to [[error burst|burst error]]s that may occur due to channel impairments, and because erroneous output of the convolutional code itself is bursty. Additionally, an [[interleaving]] layer may be used that spreads burst errors across a wider range. ▼'''Inner Code : short blocks''' <br>
▲Typically, the inner code is not a block code but a soft-decision [[convolutional code|convolutional]] [[Viterbi decoder|Viterbi-decoded]] code with a short constraint length. For the outer code, a longer hard-decision block code, frequently [[Reed Solomon]] with 8-bit symbols, is selected.
The popularizationcombination of thean inner Viterbi convolutional code with an outer Reed-Solomon code, known as an RSV code , camebecame withthe most popular construction, and was already used on the [[Voyager Program]]probes. Concatenated codesIt areis still in use today for deep-space and [[satellite communication]], notably the [[DVB-S]] [[digital television]] broadcast standard. ▼'''Outer Code : long blocks''' <br>
The larger symbol size of the Outer Code (typically a Reed-Solomon code) makes the outer code more robust to [[error burst|burst error]]s that may occur due to channel impairments. Reed-Solomon codes typically exhibit bursty error state conditions, but this misbehaviour can be turned to advantage with the concatenation method.
Additionally, an [[interleaving|interleaver]] layer (similar to the interleaver mechanism used by [[NICAM]]) may be used that spreads burst errors across a wider range.
The combination of an inner ''Viterbi convolutional code'' with an outer ''Reed-Solomon code'' (known as an RSV code) became the most popular construction use of code concatenation.
▲The popularization of the RSV code came with the [[Voyager Program]]. Concatenated codes are still in use today for deep-space and [[satellite communication]], notably the [[DVB-S]] [[digital television]] broadcast standard.
'''Concatenation without Reed-Solomon-Viterbi''' <br>
In a more loose sense, any (serial) combination of two or more codes may be referred to as a concatenated code. For example, within the [[DVB-S2]] standard, a highly efficient [[LDPC code]] is combined with an algebraic outer code in order to remove any resilient errors left over from the inner LDPC code due to its inherent [[error floor]].
'''Concatenated Reed-Solomon''' <br>
Some error correction systems have been designed that use only Reed-Solomon codes.
* The Compact Disc and DVD used concatenated Reed-Solomon codes only, with some windowing mechanisms to partly achieve the effect of a more complex interleaver.
* Single mode Concatenated Reed-Solomon codes have not found much use outside of recordable media.
* ATSC uses concatenated Reed-Solomon codes, but the DVB-T family of TV transmission systems does not.
== Turbo codes: A parallel concatenation approach ==
== External links ==
* {{scholarpedia|title=Concatenated codes|urlname=Concatenated_codes|curator=[[Dave Forney]]}}
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