\documentclass{article}
\usepackage{tikz}
\usepackage{verbatim}
\usepackage[active,tightpage]{preview}
\PreviewEnvironment{tikzpicture}
\setlength\PreviewBorder{5pt}
\usetikzlibrary{matrix}
\begin{document}
\begin{tikzpicture}
\matrix (m) [matrix of math nodes,row sep=1em,column sep=1em,minimum width=1em]
{
x(t_1) & x(t_2) & \dots & x(t_{N/2}) & x(t_{N/2+1}) & x(t_{N/2+2}) & \dots & x(t_{N}) \\
\otimes & \otimes & \dots & \otimes & & & & \\
y(t_1) & y(t_2) & \dots & y(t_{N/2}) & & & & \\
};
\path[-stealth]
(m-1-1) edge node [left] {} (m-2-1)
(m-1-2) edge node [left] {} (m-2-2)
(m-1-4) edge node [left] {} (m-2-4)
(m-1-5) edge node [left] {} (m-2-1)
(m-1-6) edge node [left] {} (m-2-2)
(m-1-8) edge node [left] {} (m-2-4)
(m-2-1) edge node [left] {} (m-3-1)
(m-2-2) edge node [left] {} (m-3-2)
(m-2-4) edge node [left] {} (m-3-4)
;
\end{tikzpicture}
\end{document}