Accurate Localization of Tagged Objects Using Mobile RFID-Augmented Robots

This paper studies the problem of tag localization using RFID-augmented robots, which is practically important for promising warehousing applications, e.g., automatic item fetching and misplacement detection. Existing RFID localization systems suffer from one or more of following limitations: requiring specialized devices; only 2D localization is enabled; having blind zone for mobile localization; low scalability. In this paper, we use Commercial Off-The-Shelf (COTS) robot and RFID devices to implement a Mobile RF-robot Localization (MRL) system. Specifically, when the RFID-augmented robot moves along the straight aisle in a warehouse, the reader keeps reading the target tag via two vertically deployed antennas (<inline-formula><tex-math notation="LaTeX">$\mathcal {R}_1$</tex-math><alternatives><mml:math><mml:msub><mml:mi mathvariant="script">R</mml:mi><mml:mn>1</mml:mn></mml:msub></mml:math><inline-graphic xlink:href="liu-ieq1-2962129.gif"/></alternatives></inline-formula> and <inline-formula><tex-math notation="LaTeX">$\mathcal {R}_2$</tex-math><alternatives><mml:math><mml:msub><mml:mi mathvariant="script">R</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:math><inline-graphic xlink:href="liu-ieq2-2962129.gif"/></alternatives></inline-formula>) and returns the tag phase data with timestamps to the server. We take three points in the phase profile of antenna <inline-formula><tex-math notation="LaTeX">$\mathcal {R}_1$</tex-math><alternatives><mml:math><mml:msub><mml:mi mathvariant="script">R</mml:mi><mml:mn>1</mml:mn></mml:msub></mml:math><inline-graphic xlink:href="liu-ieq3-2962129.gif"/></alternatives></inline-formula> and leverage the spatial and temporal changes inherent in this phase triad to construct an equation set. By solving it, we achieve the location of target tag relative to the trajectory of antenna <inline-formula><tex-math notation="LaTeX">$\mathcal {R}_1$</tex-math><alternatives><mml:math><mml:msub><mml:mi mathvariant="script">R</mml:mi><mml:mn>1</mml:mn></mml:msub></mml:math><inline-graphic xlink:href="liu-ieq4-2962129.gif"/></alternatives></inline-formula>. Based on different phase triads, we can have candidate locations of the target tag with different accuracy. Then, we propose theoretical analysis to quantify the deviation of each localization result. A fine-grained localization result can be achieved by assigning larger weights to the localization results with smaller deviations. Similarly, we can also calculate the relative location of target tag with respect to the trajectory of antenna <inline-formula><tex-math notation="LaTeX">$\mathcal {R}_2$</tex-math><alternatives><mml:math><mml:msub><mml:mi mathvariant="script">R</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:math><inline-graphic xlink:href="liu-ieq5-2962129.gif"/></alternatives></inline-formula>. Leveraging the geometric relationships among target tag and antenna trajectories, we eventually calculate the location of target tag in 3D space. We perform various experiments to evaluate the performance of the MRL system and results show that the proposed MRL system can achieve high accuracy in both 2D and 3D localization.