Backscatter Communication Signals Of Uhf Rfid Tags:Study And Applications

From the very beginning idea till now,people have explored Radio Frequency IDentification(RFID)technology for more than 70 years.Unremitting efforts of numerous researchers drive the development of RFID.Challenges such as energy absorbing,modulating signals on backscattered radio and signal collision have been solved.Global standards of RFID are set.Nowadays,as an important realization carrier of Internet of Things(IoT),RFID technology is adopted in many fields benefiting mankind,such as retails,medicine,logistics,manufacturing industry and transportation.However,most RFID systems can only identify tagged objects and track them coarsely.This paper explores how to extend the ability and applications of RFID technology.To realize the goal,we study the backscattered signals of Ultra High Frequency(UHF)RFID tags.We find that signals from tags are very sensitive to the environment.Many events will cause signals changing,such as changes of distance between tag and reader antenna,people moving around and people picking the tag.Three indicators provided by commercial UHF RFID readers,which are Received Signal Strength(RSS),phase and doppler frequency shift,help us capture changes of tag signals.Based on these findings,we research in three aspects to extend ability of RFID technology.First,we propose BackPos,a system which employs phase values to locate target tag accurately.BackPos uses difference of phases of target tag to two antennas to remove tag diversity impact and employs distance difference constraint to eliminate phase periodicity.We define a feasible region in which all positions meet distance difference constraint and relax the antenna spacing requirement,so that BackPos applies to big circular-polarized antennas.Compared to other tag localization work,BackPos don't demand reference tags and can locate tags of different types.Second,we research the relation between doppler frequency shift and relative location of user and tags and propose an item-level indoor navigation system.We find that doppler frequency shift that reader presents is highly related to multipath effect.When user blocks the Line Of Sight(LOS)signal,doppler frequency shift fluctuates largely.We design an algorithm to detect whether user reaches the location of target tag and apply it to the proposed navigation system.Third,we study the impacts of different user actions on target tag's signals.Based on these studies,we propose a system,i.e.Tagbooth,to automatically collect shopping action data of consumers for physical stores.Tagbooth detects moving tags by extracting RSS changes of low fluctuation frequency and recognize different actions based on phase changing step length after eliminating periodicity.All these works are done on commercial RFID devices.Therefore,proposed methods in this paper can be applied to existing RFID systems.Generally speaking,research of this paper,as described above,develops new abilities of RFID technology.