A Framework to Determine Secure Distances for Either Drones or Robots Based Inventory Management Systems

We propose a framework to determine a secure distance between a drone with an ultrahigh-frequency band radio frequency identification (UHF band RFID) reader and metallic objects affixed with RFID tags. The secure distance avoids order changes in received signal strength indicator (RSSI) values among the identified RFID tags in the field of view of the RFID reader. This distance enables a drone operator to securely operate the drone while identifying the RFID tag on the front of an object based on the measurements of RSSI values. An RFID tag located on the front of an object provides the maximum RSSI value. However, multipath propagation alters the RSSI values. Therefore, a framework is needed to determine a secure distance considering the multipath effects. Although inventory management systems based on drones and RFID systems have been proposed to date, this article establishes a framework to determine the secure distance. In the proposed framework, RFID tag and reader radiation patterns and multipath propagation effects were considered. The proposed framework was evaluated theoretically and experimentally. To evaluate and demonstrate the secure distance, we measured the RSSI values of two RFID tags attached to a metallic balcony. The height from the ground and spacing of the two RFID tags were 1.5 m and 1.3 m, respectively. In this environment, the secure distance was 3.8 m. The experimentally obtained distance that avoids order changes in RSSI values corresponded well with that obtained by this framework. The proposed secure distance is crucial when either drones or robots are introduced to inventory management systems.