WiSh: Towards a Wireless Shape-aware World using Passive RFIDs.

This paper presents WiSh, a solution that makes ordinary surfaces shape-aware, relaying their real-time geometry directly to a user's handheld device. WiSh achieves this using inexpensive, light-weight and battery-free RFID tags attached to these surfaces tracked from a compact single-antenna RFID reader. In doing so, WiSh enables several novel applications: shape-aware clothing that can detect a user's posture, interactive shape-aware toys or even shape-aware bridges that report their structural health. WiSh's core algorithm infers the shape of ordinary surfaces using the wireless channels of signals reflected off RFID tags received at a single-antenna RFID reader. Indeed, locating every RFID tag using a single channel measurement per-tag is challenging, given that neither their 3-D coordinates nor orientation are known a priori. WiSh presents a novel algorithm that models the geometric constraints between the coordinates of the RFID tags based on flexibility of the surface upon which they are mounted. By inferring surface curvature parameters rather than the locations of individual RFID tags, we greatly reduce the number of variables our system needs to compute. Further, WiSh overcomes a variety of system-level challenges stemming from signal multipath, stretching of fabric and modeling large surfaces. We implement WiSh on commodity RFID readers and tags attached to a variety of surfaces and demonstrate mm-accurate shape-tracking across various applications.