## 2 Study Area  
In South Korea, mining companies are actively introducing safety management systems to mining sites. At an underground mine, wireless access points (APs) have been installed at various locations within the mine to create a wireless communications network. The current locations of haulage equipment are transmitted to a web server in real time via the wireless communications network, and the transmitted data are visualized on a dashboard in a situation room located outside the mine. This study selected Baek Kwang Mineral Products Co., Ltd.'s Yeongcheon underground mine (37\({}^{\circ}\)4\({}^{\prime}\)14\({}^{\prime\prime}\), 128\({}^{\circ}\)18\({}^{\prime}\)46\({}^{\prime\prime}\)) located in the city of Danyang in the Chungcheong province of South Korea as the study area. This mine produces 1.2 million tons of high-grade limestone ore annually through a room and pillar mining method. Figure 1 shows the arrangement of the five operation sites, which consist of a drift and three levels, and the location of the outdoor crushing sites. The drift's average altitude above sea level is 313.4 m, and the lowermost level's (Level 3) average altitude above sea level is 221.6 m.  
At the Yeongcheon mine, 30-ton trucks travel back and forth between the loading sites and outdoor crushing sites to haul the ore. Production operation managers analyze ore production amounts, dispatch dump trucks in real time, and inform truck drivers of their destinations. The truck drivers follow haulage paths and travel to the loading sites located within the mine. The loaders that are waiting at the loading sites load the ore into the dump trucks. The dump trucks move to the outdoor crushing site, and the amount of ore that is piled in the crusher is checked. If this amount is below the  
Figure 1: Aerial view of the study area showing drifts inside the mine and outside facilities. (Image source: National Geographic Information Institute of South Korea). limit capacity, the ore is dropped in the crusher. If the ore exceeds a fixed capacity, the ore is piled at an outdoor storage site. The truck that dropped off the ore receives another destination from a production operation manager and moves to the mine entrance. Figure 2 shows the components of the mine safety management system installed in the study area. To create the wireless communications network, 37 ultra-wideband (UWB) wireless APs were installed in the mine and three 900-MHz wireless APs were installed at the crushing site and the outdoor storage site outside the mine. Through the wireless communications network, the locations of the production equipment in the mine could be visualized in real time on the dashboard installed in the mine's exterior office. Table 1 shows the communication protocol format of the packet data acquired by the mine safety management system. The packet data can be classified as tag recognition data and environment monitoring data, and each types of data occupies 20 bytes. When packet data are transferred to the web server, they are preceded by the transmission date, time, and the IP address of the wireless AP that transmits the data. The communication protocol places STX and ETX, which indicate the packet's start and end, at the front and end of the packet data. CHKSUM is included, which is the sum of all the values from after STX to before the check sum. Command packets include useful information acquired by the wireless APs. Tag recognition packet data include the data category, presence of an emergency situation, tag recognition sequence, recognized tag's ID, and distance between the wireless AP and tag. The tag sequence consists of a number between 0 and 255, and it is incremented by 1 in 1 s. After 255, it changes back to 0. In other words, this value indicates the order of tag recognition and how much time has elapsed since the previous tag recognition occurred.