A Research On Single RFID Tag Positioning In Indoor Environment

With the development of mobile devices and telecommunication technologies,such as mo-bile phones,tablet computers,wearable devices and the usage of 4G,5G,Internet of Things has an unprecedented development speed,which makes our society more intelligent.At the same time,the demand for location-awareness services increases sharply.For both indoor and outdoor environment,gaining user's location continuously and reliably could largely improve user's experience.Outdoor localization technologies and location-based services based on GPS are sophisticated,such as driving navigation and missile guidance.As our society is becom-ing more and more intelligent,indoor localiztion is playing a more and more important role in our life,such as guidance in airports or huge shopping malls,surveillance of patients or medical equipments in hospitals etc.However,GPS signal is hard to penetrate through buildings,and the prescience of civil usage of GPS is about 10 meters,while indoor localization needs prescience of sub-meter.Thus,it is inefficient to use GPS in indoor localization system.Radio frequency identification(RFID)is a promising candidate for indoor localization.It is a non-contact,automatic recognisable technology,which is also waterproof,magic-proof,cost-effective and has large query distance.Currently,RFID is largely used in logistics,entry control systems and assets managements.For an indoor localization system,to balance localization accuracy and system cost is always a challenge.RFID is a promising technology to achieve both goals,because of its reasonable system price and reliability.In this article,we propose a novel RFID indoor localization system based on passive RFID tag.This system combines angle of arrival(AoA)and phase of arrival(PoA)methods to estimate target's position.It leverages RFID' s two experimental signal diffusion characteristics for AoA estimation.One is that the interrogation zone is constrained in a lobe,and only in this area the tag can be queried.The second is that there exits a stable RSS pattern on angle changes.Our system consecutively uses the two features to find a general area first and then to pinpoint the AoA.By doing this,it effectively narrows the sampling zone(where signal needs to be sampled),and helps to reduce computational complexity.In addition,it reduces the multipath effect on range estimation by first determining the AoA and then rotating the reader into the direction of the target.Moreover,we exploit two signals with slight frequency difference to eliminate the phase ambiguity issue.This system takes only one reader and achieves mean accuracy of 23 cm.The simplicity and effectiveness of our system make it convenient to be used in practice.