"...state-of-the-art RFID localization systems fall under two categories. The first category operates with off-the-shelf narrowband RFID tags but makes restrictive assumptions on the environment or the tag’s movement patterns. The second category does not make such restrictive assumptions; however, it requires designing new ultrawideband hardware for RFIDs and uses the large bandwidth to directly compute a tag’s 3D location. Hence, while the first category is restrictive, the second one requires replacing the billions of RFIDs already produced and deployed annually. This paper presents RFind, a new technology that brings the benefits of ultra-wideband localization to the billions of RFIDs in today’s world. RFind does not require changing today’s passive narrowband RFID tags. Instead, it leverages their underlying physical properties to emulate a very large bandwidth and uses it for localization. Our empirical results demonstrate that RFind can emulate over 220MHz of bandwidth on tags designed with a communication bandwidth of only tens to hundreds of kHz, while remaining compliant with FCC regulations. This, combined with a new super resolution algorithm over this bandwidth, enables RFind to perform 3D localization with sub-centimeter accuracy in each of the x/y/z dimensions, without making any restrictive assumptions on the tag’s motion or the environment." 

Read the paper - http://www.mit.edu/~fadel/papers/RFind-paper.pdf

More about the project - https://www.media.mit.edu/projects/rfid-localization/overview/