= Channel code
{title2=$c:\{1,\ldots,m\}\to\mathcal X^n,\quad d:\mathcal Y^n\to\{1,\ldots,m\}$}
A deterministic fixed-length channel code consists of a <channel encoder> $c$ and a <channel decoder> $d$. It represents $m$ possible messages by length-$n$ input <codewords> for a <communication channel>, and estimates the message from the resulting output word. Its <code rate> is $(\log_2m)/n$ <bits> per <channel> use. The <maximal decoding error probability> requires reliable recovery of every message, while an average error criterion depends on the chosen message <probability distribution>.
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