%%% outline %------------------------------------------------------------------------- \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 [->,thick,] (s.east) -- (t.west) node [pos=0.5,draw,fill=white] {噪声信道}; \draw[->,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} %---------------------------------------------------------------------
