RF-based inertial measurement

Inertial measurements are critical to almost any mobile applications. It is usually achieved by dedicated sensors (e.g., accelerometer, gyroscope) that suffer from significant accumulative errors. This paper presents RIM, an RF-based Inertial Measurement system for precise motion processing. RIM turns a commodity WiFi device into an Inertial Measurement Unit (IMU) that can accurately track moving distance, heading direction, and rotating angle, requiring no additional infrastructure but a single arbitrarily placed Access Point (AP) whose location is unknown. RIM makes three key technical contributions. First, it presents a spatial-temporal virtual antenna retracing scheme that leverages multipath profiles as virtual antennas and underpins measurements of distance and orientation using commercial WiFi. Second, it introduces a super-resolution virtual antenna alignment algorithm that resolves sub-centimeter movements. Third, it presents an approach to handle measurement noises and thus delivers an accurate and robust system. Our experiments, over a multipath rich area of > 1,000 m2 with one single AP, show that RIM achieves a median error in moving distance of 2.3 cm and 8.4 cm for short-range and long-distance tracking respectively, and 6.1° mean error in heading direction, all significantly outperforming dedicated inertial sensors. We also demonstrate multiple RIM-enabled applications with great performance, including indoor tracking, handwriting, and gesture control.