\documentclass[border=5pt]{standalone}
\usepackage{tikz}
\usetikzlibrary{decorations.pathreplacing,decorations.markings,snakes,decorations.pathmorphing}

\begin{document}
\begin{tikzpicture}
\draw[ultra thick] (1.75,1.75) -- (2.25,2.25);
\draw[ultra thick] (2.75,0.75) -- (3.25,1.25);
\draw[ultra thick] (3.75,-0.25) -- (4.25,0.25);
\draw[ultra thick] (4.75,-1.25) -- (5.25,-0.75);
\draw[ultra thick] (0.75,1.75) -- (1.75,1.75) -- (1.75,0.75) -- (2.75,0.75) -- (2.75,-0.25) -- (3.75,-0.25) -- (3.75,-1.25) -- (4.75,-1.25) -- (4.75,-2.25) -- (5.75,-2.25);
\draw[ultra thick] (1,0) -- (1.75,0.75);
\draw[ultra thick] (2,-1) -- (2.75,-0.25);
\draw[ultra thick] (3,-2) -- (3.75,-1.25);
\draw[ultra thick] (4,-3) -- (4.75,-2.25);
\draw[ultra thick] (0,0) -- (1,0) -- (1,-1) -- (2,-1) -- (2,-2) -- (3,-2) -- (3,-3) -- (4,-3) -- (4,-4) -- (5,-4);
\draw[ultra thick] (1,-1) -- (0.5,-1.5);
\draw[ultra thick] (2,-2) -- (1.5,-2.5);
\draw[ultra thick] (3,-3) -- (2.5,-3.5);
\draw[ultra thick] (4,-4) -- (3.5,-4.5);

\node at (0.55,1.75) {\footnotesize $a$}; 
\node at (5.95,-2.25) {\footnotesize $a$}; 
\node at (-0.05,0.25) {\footnotesize $b$}; 
\node at (5,-4.3) {\footnotesize $b$}; 
\node at (2.4,2.4) {\footnotesize $1$};
\node at (3.4,1.4) {\footnotesize $2$};
\node at (4.4,0.4) {\footnotesize $3$};
\node at (5.4,-0.6) {\footnotesize $4$};
\node at (0.35,-1.65) {\footnotesize $1$};
\node at (1.35,-2.65) {\footnotesize $2$};
\node at (2.35,-3.65) {\footnotesize $3$};
\node at (3.35,-4.65) {\footnotesize $4$};

\draw[<->,green!50!black] (2,1.9) -- (2.9,1);
\node[green!50!black] at (2.7,1.7) {\footnotesize $\widehat{a}_1^{(1)}$};
\draw[<->,green!50!black] (3,0.9) -- (3.9,0);
\node[green!50!black] at (3.7,0.7) {\footnotesize $\widehat{a}_2^{(1)}$};
\draw[<->,green!50!black] (4,-0.1) -- (4.9,-1);
\node[green!50!black] at (4.7,-0.3) {\footnotesize $\widehat{a}_3^{(1)}$};

\draw[<->,green!50!black] (1.3,0.2) -- (2.2,-0.7);
\node[green!50!black] at (2,0) {\footnotesize $\widehat{a}_1^{(2)}$};
\draw[<->,green!50!black] (2.3,-0.8) -- (3.2,-1.7);
\node[green!50!black] at (3,-1) {\footnotesize $\widehat{a}_2^{(2)}$};
\draw[<->,green!50!black] (3.3,-1.8) -- (4.2,-2.7);
\node[green!50!black] at (4,-2) {\footnotesize $\widehat{a}_3^{(2)}$};

\draw[dashed] (1.75,1.75) -- (-0.325,-0.325);
\draw[dashed] (5,-4) -- (5.5,-4);

\draw[<->,green!50!black] (2.7,2.7) -- (6.7,-1.3);
\node[green!50!black] at (4.75,0.95) {\footnotesize{\bf $\rho$}};
\draw[<->,green!50!black] (-0.25,-0.35) -- (0.65,-1.25);
\node[green!50!black] at (0.4,-0.65) {\footnotesize{\bf $S$}};
\draw[<->,green!50!black] (0.9,0.1) -- (0.9,1.65);
\node[green!50!black] at (0.65,1.3) {\footnotesize{\bf $\tau_1$}};
\draw[<->,green!50!black] (5.45,-0.85) -- (5.45,-3.9);
\node[green!50!black] at (5.25,-3) {\footnotesize{\bf $\tau$}};

\draw[blue,fill=blue] (1.75,1.75) circle (0.1cm);
\node[scale=0.7,blue] at (1.45,1.95) {\footnotesize{\bf $(1,1)$}};
\draw[blue,fill=blue] (2.75,0.75) circle (0.1cm);
\node[scale=0.7,blue] at (2.45,0.95) {\footnotesize{\bf $(2,1)$}};
\draw[blue,fill=blue] (3.75,-0.25) circle (0.1cm);
\node[scale=0.7,blue] at (3.45,-0.05) {\footnotesize{\bf $(3,1)$}};
\draw[blue,fill=blue] (4.75,-1.25) circle (0.1cm);
\node[scale=0.7,blue] at (4.45,-1.05) {\footnotesize{\bf $(4,1)$}};

\draw[blue,fill=blue] (1,0) circle (0.1cm);
\node[scale=0.7,blue] at (0.65,-0.2) {\footnotesize{\bf $(1,2)$}};
\draw[blue,fill=blue] (2,-1) circle (0.1cm);
\node[scale=0.7,blue] at (1.65,-1.2) {\footnotesize{\bf $(2,2)$}};
\draw[blue,fill=blue] (3,-2) circle (0.1cm);
\node[scale=0.7,blue] at (2.65,-2.2) {\footnotesize{\bf $(3,2)$}};
\draw[blue,fill=blue] (4,-3) circle (0.1cm);
\node[scale=0.7,blue] at (3.65,-3.2) {\footnotesize{\bf $(4,2)$}};
\end{tikzpicture}
\end{document}