I have four images and i want to put them on top of the page side by side. I am writing on a two column document format. I drew the following picture to show how i want the pictures to look. I tried using minipage environment within figure* , but didn't work . Please advice.

I also tried using this link, didn't work for me. link Here is the code i tried using.
\begin{figure*}
\centering
\begin{minipage}[b]{0.3\textwidth}
\includegraphics[width=0.2\textwidth]{single_hop_wireless1.jpg}
\caption{Pre processing memory graph}
\end{minipage}
\begin{minipage}[b]{0.3\textwidth}
\includegraphics[width=0.2\textwidth]{single_hop_wireless2.jpg}
\caption{Post processing memory graph}
\end{minipage}
\begin{minipage}[b]{0.3\textwidth}
\includegraphics[width=0.2\textwidth]{single_hop_wireless3.jpg}
\caption{Pre processing JVM memory graph}
\end{minipage}
\begin{minipage}[b]{0.3\textwidth}
\includegraphics[width=0.2\textwidth]{single_hop_wireless4.jpg}
\caption{Post processing JVM memory graph}
\end{minipage}
\end{figure*}
Thanks in advance.
