I. Introduction
The number of mobile device users including smartphone users has rapidly been increasing in the world, and various convenient and useful smartphone applications have been developed. Now smartphones not only work the ordinary internal processes such as dial and receive phone calls, send text messages, and do mobile banking wherever we are, but they also are coming to control various other devices in our real everyday lives. Through smartphones and mobile applications, we can remotely control a variety of external devices such as TVs, projectors for presentations, computers, and even cars.