I. Introduction
Gesture-based interfaces provide an intuitive way for users to specify commands and interact with computers [1]. Existing gesture recognition systems can be classified into three types: motion-based, touch-based, and vision-based systems. For motion-based systems [2], [3], a user must hold a mobile device or an external controller to make gestures. Touch-based systems [4], [5] can accurately map the finger/pen positions and moving directions on the touch-screen to different commands. However, 3D gestures are not supported because all possible gestures are confined within the 2D screen surface. While the first two types of system require users to make contact with devices, vision-based systems [1], [6] using camera and computer vision techniques allow users to make intuitive gestures without touching the device. However, vision-based systems are computationally expensive and power-consuming, which are undesirable for resource-limited mobile devices like tablets or mobile phones.