\begin{tikzpicture}[->, >=stealth, shorten >= 0pt, draw=black!50, node distance=3.2cm, font=\sffamily]
    \tikzstyle{node}=[circle,fill=black,minimum size=2pt,inner sep=0pt]
    \tikzstyle{block}=[draw=black,rectangle,fill=none,minimum size=1.5cm, inner sep=0pt]

	\node[node] (xc) {};
    \node[block, right=1cm of xc, text width = 1.5cm, align= center] (DSP) {$H(z)$};
	\node[node, right=1cm of DSP] (yc) {};
			
    \path (xc) edge (DSP);
    \path (DSP) edge (yc);
    
    \node[above = 0mm of xc, text width = 1cm, align=center] {$v[n]$};
    \node[above = 0mm of yc, text width = 3cm, align=center] {$\hat{s}[n] \approx s[n]$};
         
    \ifdefined\INVERSE
    	\node[block, right=1cm of yc, text width = 1.5cm, align= center] (inv) {$H^{-1}(z)$};
    	\node[node, right=1cm of inv] (xpred) {};
    	\node[above = 0mm of xpred, text width = 1cm, align=center] {$\tilde{v}[n]$};
	    \path (yc) edge (inv);
    	\path (inv) edge (xpred);
    \else\relax    	
    \fi
\end{tikzpicture}