Montage: Combine Frames with Movement Continuity for Realtime Multi-User Tracking

In this work, we design and develop <italic>Montage</italic> for real-time multi-user formation tracking and localization by off-the-shelf smartphones. <italic>Montage</italic> achieves submeter-level tracking accuracy by integrating temporal and spatial constraints from user <italic>movement vector</italic> estimation and distance measuring. In <italic>Montage</italic>, we designed a suite of novel techniques to surmount a variety of challenges in real-time tracking, without infrastructure and fingerprints, and without any a priori user-specific (e.g., stride-length and phone-placement) or site-specific (e.g., digitalized map) knowledge: (1) a coded audio tone to support multi-user tracking with minimal latency, in the presence of high noise, multi-path effect, and Doppler Shift, (2) an innovative stride-length and walking direction estimation method without a priori knowledge of user and site, and (3) a vector-based multi-user tracking scheme which connects successive localization snapshots to refine users’ locations and generate continuous moving traces. We implemented, deployed, and evaluated <italic>Montage </italic> in both outdoor and indoor environment. Our experimental results (847 traces from 15 users) show that the stride-length estimated by <italic>Montage</italic> over all users has error within <inline-formula> <tex-math notation="LaTeX">$9\text{\,cm}$</tex-math><alternatives><inline-graphic xlink:href="zhang-ieq1-2577586.gif"/> </alternatives></inline-formula>, and the moving-direction estimated by <italic>Montage</italic> is within <inline-formula><tex-math notation="LaTeX">$20$</tex-math><alternatives> <inline-graphic xlink:href="zhang-ieq2-2577586.gif"/></alternatives></inline-formula> degrees. For real-time tracking, <italic>Montage</italic> provides meter-second-level formation tracking accuracy with off-the-shelf mobile phones.