\begin{tikzpicture}[>=latex']
  \tikzset{block/.style= {draw, rectangle, align=center},
  }
  \node [coordinate]  (start) {};

  \node [coordinate, above = +6mm of start]  (src1) {};
  \node [coordinate, above = +2mm of start]  (src2) {};
  \node [coordinate, above = -2mm of start]  (src3) {};
  \node [coordinate, above = -6mm of start]  (src4) {};

  \node [coordinate, right = 16mm of src1] (inp1) {};
  \node [coordinate, right = 16mm of src2] (inp2) {};
  \node [coordinate, right = 16mm of src3] (inp3) {};
  \node [coordinate, right = 16mm of src4] (inp4) {};

  \node [coordinate, above = +6mm of inp1] (inp0) {};
  \node [coordinate, left = 8mm of inp0] (src0) {};

  \node [coordinate] (inpm) at ($(inp0)!0.5!(inp4)$) {};
  \node [coordinate] (inpc) at ($(inp1)!0.5!(inp4)$) {};

  \node [block, minimum height = 16mm, minimum width = 15mm, right = 00mm of inpc] (COMB) {Comb\\$\wval_{j\to i}$};   

  \node [block, draw, minimum width = 15mm, right = 00mm of inp0] (WTF) {$\wfbk$};

  \node [circle, draw, radius = 3mm, right = 8mm of COMB] (SUM) {$+$};

  \node [block, right = 6mm of SUM] (INTG){Integr\\$+$\\Trigger}; 

  \node [coordinate, right = 15mm of INTG] (FORK){}; 
  \node [coordinate, above = 20mm of FORK] (ELBOW){};       
  \node [coordinate, right = 8mm of FORK] (end){};

  \node [block, draw=red, right = -4mm of inpm, minimum height = 28mm, minimum width = 58mm] (BOX) {};

  \draw[->] (src1) -- (inp1);
  \draw[->] (src2) -- (inp2);
  \draw[->] (src3) -- (inp3);
  \draw[->] (src4) -- (inp4);

  \draw[->] (COMB) -- (SUM) node[above,pos=0.5] {$J_i$};
  \draw[->] (INTG) -- (FORK) node[above,pos=0.5] {$X_i$};
  \draw[->] (FORK) -- (end);
  \draw[->] (FORK) -- (ELBOW) -| (src0) -- (inp0);
  \draw[->] (WTF) -| (SUM);
  \draw[->] (SUM) -- (INTG);
\end{tikzpicture}
