The SARFID technique for discriminating tagged items moving through a UHF-RFID gate

The discrimination of tagged items moving along a conveyor belt from other tagged items that are present in the scenario is investigated, when a UHF-RFID gate is installed at a conveyor section. Indeed, tagged items that are static or randomly moving in the scenario (nomad tags) around the reader antenna could be detected even if they are not on the conveyor (false positive readings). The classification procedure here proposed exploits the SARFID phase-based technique used to localize tags on a conveyor belt, which takes advantage of the fact that the tagged items move along a conveyor, whose path and instantaneous speed are both known. The latter can be implemented with only a firmware upgrade, in any conveyor belt scenario already equipped with an RFID system, without any modification of the system infrastructure and additional (reference tags/multiple antennas) or ad hoc hardware. From experimental results in a real scenario, the discrimination between moving tags from static/nomad tags can be obtained with an overall accuracy greater than 99.9%, by employing only one reader antenna.