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[[File:GSM convol code.png|thumb|right|400px|Stages of channel coding in GSM <ref>Eberspächer J. et al. GSM-architecture, protocols and services. – John Wiley & Sons, 2008. - p.97</ref>. Block encoder and Parity check - error detection part. Convolutional encoder and Viterbi decoder - error correction part. [[Error_correction_code#Interleaving|Interleaving]] and Deinterleaving - code words separation increasing in time ___domain and to avoid bursty distortions.]]
Convolutional codes are used extensively to achieve reliable data transfer in numerous applications, such as [[digital video]], radio, [[mobile communications]] (e.g., in GSM <ref>[http://www.scholarpedia.org/article/Global_system_for_mobile_communications_(GSM) Global system for mobile communications (GSM) (Scholarpedia)]</ref>, GPRS, EDGE and 3G networks (until 3GPP Release 7)<ref>3rd Generation Partnership Project (September 2012). "3GGP TS45.001: Technical Specification Group GSM/EDGE Radio Access Network; Physical layer on the radio path; General description". Retrieved 2013-07-20.</ref><ref>Halonen, Timo, Javier Romero, and Juan Melero, eds. GSM, GPRS and EDGE performance: evolution towards 3G/UMTS. John Wiley & Sons, 2004. - p. 430</ref>) and [[satellite communications]].<ref>Butman, S. A., L. J. Deutsch, and R. L. Miller. [http://tda.jpl.nasa.gov/progress_report/42-63/63H.PDF "Performance of concatenated codes for deep space missions."] The Telecommunications and Data Acquisition Progress Report 42-63, March–April 1981 (1981): 33-39.</ref> These codes are often implemented in [[concatenated code|concatenation]] with a hard-decision code, particularly [[Reed–Solomon error correction|Reed–Solomon]]. Prior to [[turbo codes]] such constructions were the most efficient, coming closest to the [[Shannon-Hartley theorem|Shannon limit]].
==Convolutional encoding==
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