## 2 Project Background: Wireless Data Transfer Using NFC Technology  
During the project-design stage, we focused on evaluating the suitable technology for smart-device communication with a real-time database. We first focused on mobile communication devices. As we were creating a new platform, we chose the Android operating system. The system was chosen based on a study by the Gamius portal, where it was stated that, as of December 2020, approximately 85% of users owned a smartphone with Android OS [9; 14; 15; 16]. We started creating a mobile application in the Android Studio using the Java programming language. The next step was to examine the possibilities of entering our chosen identification numbers and essential specifications into the database in real-time. We focused on the wireless connection between a smart mobile device and an NFC reader. Wireless communication is based on communication between two devices connected by other than mechanical means--for example, using electromagnetic waves, which in practice means an optical connection, or a connection using a radio signal. Wireless communication technologies include Bluetooth, Wi-Fi, ZigBee, RFID, and NFC. NFC wireless communication is commonly used nowadays; for example, when paying with an ATM card. This is the model we used. However, before tackling the NFC issue, we compared the technologies to ensure we were doing it right. We started by comparing NFC, Wi-Fi, and Bluetooth in the context of wireless communication parameters. The comparison is shown in Figure 1. The choice was also influenced by the goal of simple, fast, and transparent patient queuing using a mobile communication device. NFC technology enables wireless data transfer between two devices tuned to the same transmission frequency. The transmission uses radiofrequency electromagnetic fields with a frequency of \(f=13.56\) MHz and a relatively low transmission speed. This varies depending on the communication standard used and the transmission distance, which is usually in the range of several millimetres. At the same time, with NFC, it is explicitly stated that two devices that communicate must be located close enough to each other that eavesdropping is very unlikely. Such devices have an inherently high level of security. The communication mechanism is based on the use of the phenomenon of electromagnetic induction, Figure 2.  
The source of the EM signal is a transmitter that creates a time-varying electromagnetic field in its surroundings. The target device is the receiver that is within the range of the broadcasted field. The fundamental characteristics of NFC communication are listed in Figure 3; these are the basic communication and operating modes of the technology and include the direction of communication and the standards and parameters that are used in wireless NFC communication. ISO/IEC 7816-4 is an international standard for contactless mobile devices and electronic identity cards [17]. The APDU used for NFC communication between the device and the reader is described in ISO/IEC 7816-12. An APDU can take two forms, one of which is a command delivered from an NFC reader to a device that emulates a card. The response, on the other hand, is divided into a header and sent data. The message body can have different proportions. To initiate a connection, an appropriate service must be selected, as  
Figure 1: Mobile communication devices: comparison of available wireless technologies. Figure 2: NFC technology and its basic principle: individual modes of communication used in the designed application. described in ISO/IEC 7816-4. The standard defines AIDs or application IDs that are usually published to avoid conflicts between internationally used AIDs. Among the most well-known registered AIDs are companies that accept ATM card payments, such as Mastercard and Visa. Unregistered AIDs must begin with the letter F followed by a hexadecimal combination of numbers and characters as specified by the application developers [18; 19; 20].