A Cartesian Robot for RFID Signal Distribution Model Verification

Abstract

In our previous research, we addressed the problem of automating the design of passive radio-frequency (PRF) services. An optimal PRF surface is one that offers a maximum probability of localization at a minimum instrumentation cost, i.e., a minimum number of surface-embedded passive RFID transponders. Our previous results were based on the assumption that the signal distribution model of an individual RFID transponder can be approximated as a circle. The problem of automated PRF surface design was then formulated as the problem of packing a surface with circles of a given radius. However, in practice, this approach leads to some loss of optimality: some areas of the surface may not be covered or too many transponders may be required. More exact methods are need for verifying and constructing signal distribution models of surface-embedded RFID transponders that can be used by surface packing algorithms to optimize the design. In this paper, we present the design and implementation of a Cartesian robot for verifying and constructing signal distribution models of surface-embedded RFID transponders. A model is characterized by four high-level parameters: an RFID transponder, an RFID antenna, an RFID reader, and a surface type. The robot moves an RFID reader-antenna unit over a PRF surface, e.g. a carpet, and systematically collects readings for various antenna positions over the surface. The collected readings are subsequently processed to verify or construct signal distribution models. We describe experiments with the robot to verify the localization probability of automatically designed PRF surfaces. We also present experiments with the robot to verify and construct the signal distribution models of a specific RFID transponder.