A novel method for indoor positioning with passive UHF RFID

Radio frequency identification (RFID) positioning has been an emerging research topic along with the rapid development of RFID technology. Most RFID positioning systems utilise active tags, due to the challenging operational principles of passive technology. For example, received signal strength is usually one of the main factors in wireless positioning, but with passive systems, it is very non-linear and therefore difficult to use reliably. This paper presents a novel method for indoor RFID positioning where threshold power level is used instead of received signal strength and phase information of backscattered signals is exploited to precisely define the results. This method gives very accurate results in defining the distance between reader antenna and passive UHF tag. This is demonstrated with the measurements described in this paper. The distances specified using this method can be employed in determining exact locations. This method has the potential to take passive RFID positioning to a new level.