## 5 Concluding Remarks  
RFID-based real-time location awareness has been widely studied. Although passive RFID tag-based methods involve lower costs than active RFID methods, most studies have focused on the latter, with the research on the former remaining largely insufficient. Thus, we proposed a passive RFID-based inventory localization method that involved the introduction of the concept of reference tags. The proposed algorithm was programed and then applied to the MSR, consisting of four rows and five columns installed in an electronic device manufacturing company in South Korea. We confirmed the tag recognition according to the change in the measurement distance, the tag recognition interval of the RFID reader, and the number of stock items in each zone. We also verified the accuracy of the location identification for the size-expanded MSR through 20 repeated experiments. From these experiments, we found that as the number of loaded stock items is increased, the tag recognition interval of the RFID reader inversely decreases to increase the recognition rate. Furthermore, even if the tag recognition interval of the RFID reader is small, the recognition rate can be lowered when the number of loaded stock items is large. In addition, we confirmed that the proposed method provided a meaningful result, as there was no significant difference in the location identification rate compared with that of the existing active RFID tag-based methods.  
Strictly speaking, the proposed method is not a real-time location identification method, as the operator recognizes the item information in the MSR with a portable RFID reader at a specific time. However, the proposed method is relatively inexpensive to construct in terms of identifying the location of the items stacked in MSR and in relatively narrow areas using a passive tag. This advantage makes it suitable for SMEs that have issues with large-scale facility investment, applying it to compare  
Figure 8: Results of the item location identification for the 20 repeated measurements.  
the location difference between the registered location information in the inventory system and the actual location of the items in the rack.  
Despite the many advantages of the proposed method, the following issues should be addressed to make the method more practically applicable, and these issues will be the subject of future research. First, the decrease in the location identification rate should be compensated for when the tag recognition interval and the number of items loaded in each zone increase. Second, the proposed method has a restriction, as the same number of items must be loaded in each zone, and the item locations should be correctly identified, even if various numbers of items are loaded in each zone.  
All of the authors discussed and proposed the mathematical method and designed the test plan. [PERSON], [PERSON]-J.K., and B.K.L. accomplished the computation and wrote the paper. All authors have read and agreed to the published version of the manuscript.  
This work was supported by the National Research Foundation grant (NRF-2018R1C1B5033711) of the Republic of Korea.  
The authors declare no conflict of interest.