SMART: Screen-based gesture recognition on commodity mobile devices

In-Air gesture control extends a touch screen and enables contact-less interaction, thus has become a popular research direction in the past few years. Prior work has implemented this functionality based on cameras, acoustic signals, and Wi-Fi via existing hardware on commercial devices. However, these methods have low user acceptance. Solutions based on cameras and acoustic signals raise privacy concerns, while WiFi-based solutions are vulnerable to background noise. As a result, these methods are not commercialized and recent flagship smartphones have implemented in-Air gesture recognition by adding extra hardware on-board, such as mmWave radar and depth camera. The question is, can we support in-Air gesture control on legacy devices without any hardware modifications? To answer this question, in this work, we propose SMART, an in-Air gesture recognition system leveraging the screen and ambient light sensor (ALS), which are ordinary modalities on mobile devices. For the transmitter side, we design a screen display mechanism to embed spatial information and preserve the viewing experience; for the receiver side, we develop a framework to recognize gestures from low-quality ALS readings. We implement and evaluate SMART on both a tablet and several smartphones. Results show that SMART can recognize 9 types of frequently used in-Air gestures with an average accuracy of 96.1%.