Hybrid inertial microwave reflectometry for mm-scale tracking in RFID systems

Abstract

Despite the numerous wireless position estimation schemes in the patent and research literature, motion capture grade localization with RF has eluded engineering practice. Motion capture localization with cm-scale accuracy or better is typically performed optically, with limited range, high setup time, and environmental limitations (e.g. infrared systems that do not work outdoors). Today's true RF-based motion capture technology involves sensing low-frequency or DC fields using bulky sensor boxes -- with ranges of only a few meters. In this work, we achieved long-range, motion-capture grade localization with extraordinarily low-powered HIMR tags. Localization and tracking are some of the most important applications of RFID technology. This work proposes a new fine-scale (millimeter level) radio localization and tracking scheme---Hybrid Inertial Microwave Reflectometry (HIMR)---for radio frequency identification and other wireless systems. The scheme fuses the information from the backscattered radio frequency signal properties, such as received signal strength and received signal phase, along with reflected inertial data from a tag-mounted, 9-axis inertial sensor to yield millimeter level localization accuracy. Experimental results yielded a positional accuracy in the range of 2 mm and 20 mm, respectively, for one- and two-dimensional tracking of a fast-moving tag. The HIMR-scheme does not require reference tags or external system for localization, instead all the information is extracted from the RFID-based radio link and fused in novel HIMR-algorithm without performing mathematical integration or differentiation to achieve position and tracking.