## 3 Inventory Location Identification Framework in MSR
### Configuration of Tag Information  
This step starts by attaching the reference tags to the center of each MSR zone. The reference tag is used as the location recognition identifier with a known location within a predefined physical MSR zone, and the locations of the stock items are identified by referring to their adjacent reference tag's location. The reference tag has a unique identification code (UID) that provides the location of specific spaces, locating any item in the MSR. Thus, we must know the UID associated with the location area it occupies. To obtain the UID, we must physically assign a UID to the location information of the specific area and implement a mechanism to retrieve this identification. The RFID reader scans the reference tags attached to the MSR and retrieves the UID of the reference tag. This UID is then sent through a wireless communication network to the LS server. The LS server is responsible for mapping the UID to the physical location of the reference tag. To map the reference tag's UID to the physical location in the MSR, the mapping information for all reference tags should be registered into the database implemented at the LS server in advance. The relationship between the RFID reader and LS is based on a client-server scheme, where the client represents the RFID reader and the server represents the LS where the location information is presented. A Wi-Fi connection is used to communicate the client and the server and is based on the transmission control protocol and Internet protocol suite (TCP-IP). To better understand this, let us suppose that there is an MSR with four zones. When a reference tag with a UID of ee0010 is attached to Zone #1, the mapping information can be defined as [ee0010, Zone 1]. The mapping information is then registered in the database through the LS. To refer to the reference tag as the location identifier of other stock items, we must adjust the recognition range of the RFID reader. To better understand, let us consider the example shown in Figure 2. When the RFID reader generates radio waves through the connected antenna, the recognizable range of the RFID reader (\(Th_{1}\) or \(Th_{2}\)) depends on the propagation angle (\(\theta_{1}\) or \(\theta_{2}\)) and intensity that are related to the radio-wave reaching distance (\(lh_{1}\) or \(lh_{2}\)). Generally, the propagation angle and intensity of the RFID reader are slightly different depending on the manufacturer and RFID type. If the propagation angle can be constantly fixed, then the recognizable range may vary depending on the distance between the RFID reader and target of identification (\(Rh_{1}\) or \(Rh_{2}\)). This study uses  
Figure 1: Proposed framework. a propagation angle control device to artificially fix the wave angles. In Figure 2, let RFID reader 1 and RFID reader 2 have the same propagation angle (\(\theta_{1}=\theta_{2}\)), and let RFID reader 1 be closer to the targets of identification (i.e., the tags) than RFID reader 2 (\(Rh_{1}<Rh_{2}\)). \(T\) is the center distance between two adjacent reference tags. Suppose that the RFID reader can read tags that are reachable regardless of the distance between the reader and a tag, and all the tags are within reader range while \(T\) is set to be a constant. The recognition range of RFID reader 1 is smaller than that of RFID reader 2 (\(Th_{1}<Th_{2}\)). That is, the recognizable range (\(Th\)) can be adjusted by varying the distance between the RFID reader and targets (\(Rh\)) while simultaneously fixing the propagation angle of the RFID reader. Here, we set the measurement distance so that \(Th\) should be approximately less than 2\(T\) (\(Th\lessapprox 2\times T\)) to refer to the reference tag as an identifier. As a result, the measurement distance is more likely to be determined at \(Rh_{1}\), rather than \(Rh_{2}\), because \(Th_{1}\) is less than 2 \(\times\)\(T\) in Figure 2.  
In terms of geometry, \(Th\) should be approximately less than 2\(T\) (\(Th\lessapprox 2T\)) to identify one reference tag.