\section{INTRODUCTION}
\subsection{background}
\subsection{application}
\subsection{related work}
\subsection{propose}
\subsection{challenge}
\subsection{techniques}
\subsection{contributions}
\subsection{paper organization}
\section{BACKGROUND}
\section{RELATED WORK}
\section{SYSTEM DESIGN}
\subsection{System Overview}
headphone positioning -> Head movement recognition -> Head posture tracking
\subsection{headphone positioning}