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Concatenated codes were first implemented for [[deep space]] communication in the [[Voyager program]] after the craft had finished their encounters with the outer Gas Giants.<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]].
'''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 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.▼
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.
'''Outer code : long blocks''' <br>
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 uptake and popularization of the RSV code and its use in the Voyager Program were somewhat simultainious. Concatenated codes are still in use today for deep-space and [[satellite communication]], notably the [[DVB-S]] [[digital television]] broadcast standard.▼
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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
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]].
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