## 2 State of the Art
### Application of RFID in a Simulated Production Line for an Industrial Context
In this sense, a respective production scheduling order (a vital process that involves creating a proper timetable that defines a specific order of production activities) created through the aforementioned production execution system is then sent to a specific scheduling system (electronic Kanban, a type of information transmission system that ensures that each workstation produces only what is needed for the next workstation along the production flow) that includes a physical storage station and manages the inventory of components in the context. Considering the use of a type of box (electronic Kanban kits) intended for the transport of individual components that need to be manufactured, assembled, tested, or prepared for packaging, the following aspects are realised [31]:  
* Each box of this type includes a physically applied RFID tag. Each manufactured component placed in the kit is identified via barcodes or QR codes printed on labels attached to each part or printed directly on the physical parts;
* Each set (box) is moved from one production station to another, and when a set arrives at a given station it is registered--a process that consists of reading the RFID code of the given box through an RFID reader and storing the information about its arrival in the respective database of the production execution system considered;
* Once all the physical components included in each box have been processed at the respective workstation, they are placed back in the box and the box is then checked out, according to a process that involves updating the production execution system database related to that box;
* When all the production processes related to the components stored in one of these sets have been completed, the box can be reused for another set of components and the RFID tag is rewritten. Figure 4: Learning factory in the case study (adapted from [31]). In turn, the integrated information technology/operational technology (IT/OT) infrastructure built at the learning factory makes it possible to overcome some of the challenges in adopting and implementing RFID technology, particularly concerning the risks of interference with other radio bands; the selection of tags and memory size limitations; the integration of RFID technologies into an industrial automation platform; and the use of microservices in favour of implementing RFID technologies [31]. When implementing ultra high frequency (UHF)-operating RFID technologies in specific areas, it is necessary to consider the risks of interference with other technologies at the level of radio-frequency bands in an industrial environment. In turn, applications that use frequency bands that are susceptible to clear interference (in this context of operation in equivalent frequency ranges) can be interrupted or prevented from working properly by any ultra high frequency RFID (UHF-RFID) device, in fact corresponding to a type of strong RFID reader [31]. The learning factory uses devices that utilise wireless radio-frequency technology along with 12 UHF-RFID readers. In turn, each of the readers in the factory under consideration had to be configured for the power and frequencies that facilitate successful integration with other technologies. For an optimised design, each reader was configured for a single frequency band to operate with a minimum separation of 2.0 MHz between any devices. In addition, the operating power was also optimised for read and write operations to avoid further interference. The tags were processed in 300 milliseconds and the data were available for immediate processing of the tag information. The learning factory can use different types of RFID tags and the corresponding readers for different operations and applications, with the operating parameters varying according to the different types of RFID devices being applied [31]. To this end, Table 1 shows the results of the read-range tests for these types of RFID and tag technology.