Without requiring objects to carry any transceiver, device-free based object tracking provides a promising solution for many localization and tracking systems to monitor non-cooperative objects such as intruders. However, existing device-free solutions mainly use sensors and active RFID tags, which are much more expensive compared to passive tags. In this paper, we propose a novel motion detection and tracking method using passive RFID tags, named Twins. The method leverages a newly observed phenomenon called critical state caused by interference among passive tags. We contribute to both theory and practice of such phenomenon by presenting a new interference model that perfectly explains this phenomenon and using extensive experiments to validate it. We design a practical Twins based intrusion detection scheme and implement a real prototype with commercial off-the-shelf reader and tags. The results show that Twins is effective in detecting the moving object, with low location error of 0.75m in average.
@article{arxiv.1308.6805,
title = {Twins:Device-free Object Tracking using Passive Tags},
author = {Jinsong Han and Chen Qian and Dan Ma and Xing Wang and Jizhong Zhao and Pengfeng Zhang and Wei Xi and Zhiping Jiang},
journal= {arXiv preprint arXiv:1308.6805},
year = {2013}
}