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%%% outline
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\begin{tikzpicture}

\node [draw,red,fill=red!10,thick,anchor=center,circle,inner sep=3.5pt] (s) at (0,0) {\black{$\seq{s}$}};
\node [draw,ublue,fill=blue!10,thick,anchor=center,circle,inner sep=3.3pt] (t) at ([xshift=1.5in]s.east) {\black{$\seq{t}$}};

\draw [-&gt;,thick,] (s.east) -- (t.west) node [pos=0.5,draw,fill=white] {噪声信道};
\draw[-&gt;,thick](s.east) -- ([xshift=2.2em]s.east);
\node [anchor=east] at (s.west) {\scriptsize{信宿}};
\node [anchor=west] at (t.east) {\scriptsize{信源}};

\end{tikzpicture}




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