See through walls with COTS RFID system!

Lei Yang, Qiongzheng Lin, Xiangyang Li, Tianci Liu, Yunhao Liu

Research output: Chapter in book / Conference proceedingConference article published in proceeding or bookAcademic researchpeer-review

153 Citations (Scopus)


Through-wall tracking has gained a lot of attentions in civilian applications recently. Many applications would benefit from such device-free tracking, e.g. elderly people surveillance, intruder detection, gaming, etc. In this work, we present a system, named Tadar, for tracking moving objects without instrumenting them using COTS RFID readers and tags. It works even through walls and behind closed doors. It aims to enable a see-through-wall technology that is low-cost, compact, and accessible to civilian purpose. In traditional RFID systems, tags modulate their IDs on the backscatter signals, which is vulnerable to the interferences from the ambient reflections. Unlike past work, which considers such vulnerability as detrimental, our design exploits it to detect surrounding objects even through walls. Specifically, we attach a group of RFID tags on the outer wall and logically convert them into an antenna array, receiving the signals reflected off moving objects. This paper introduces two main innovations. First, it shows how to eliminate the flash (e.g. the stronger reflections off walls) and extract the reflections from the backscatter signals. Second, it shows how to track the moving object based on HMM (Hidden Markov Model) and its reflections. To the best of our knowledge, we are the first to implement a through-wall tracking using the COTS RFID systems. Empirical measurements with a prototype show that Tadar can detect objects behind 5″ hollow wall and 8″ concrete wall, and achieve median tracking errors of 7.8cm and 20cm in the X and Y dimensions.
Original languageEnglish
Title of host publicationMobiCom 2015 - Proceedings of the 21st Annual International Conference on Mobile Computing and Networking
PublisherAssociation for Computing Machinery
Number of pages13
ISBN (Electronic)9781450336192
Publication statusPublished - 7 Sept 2015
Externally publishedYes
Event21st Annual International Conference on Mobile Computing and Networking, MobiCom 2015 - Paris, France
Duration: 7 Sept 201511 Sept 2015


Conference21st Annual International Conference on Mobile Computing and Networking, MobiCom 2015


  • RFID
  • See-through walls
  • Tadar
  • Tracking

ASJC Scopus subject areas

  • Software
  • Hardware and Architecture
  • Computer Networks and Communications


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