Fine-Scale Phase-Based Ranging Through Walls and Obstructions Using Tunneling RFID Tags

Tunneling tags have already shown their long-range capability for communications and localization in line-of-sight (LoS) with a reader operating in the 5.8 GHz band. In this paper, a received signal phase-based positioning method is investigated using semi-passive and tunneling radio frequency identification (RFID) tags in various non-line-of-sight (NLoS) environments. Experimental results show that a tunneling tag achieves gains above 10.2 dB and 19.6 dB when communicating through a cinder block and a plaster wall, respectively. When using the tunneling tag, with proper calibration, an average distance estimation accuracy of 1.33% and 2.37% is achieved in a hallway and classroom environment with clear LoS. An average estimation error of 1.03% and 2.12% is observed in through-obstruction and through-wall NLOS conditions, respectively.