## 3 Results and Discussion  
The general structure of the three-shaft underground mine communication system shown in Figure 1 is illustrated for the Motorola Dimetra (TETRA) communication system, for the first one-shaft underground mine communication system, Oyutolgoi mine communication system failure data (see Supplementary Materials) was used and modeled using availability information (see Supplementary Materials) provided by the manufacturer of the Motorola Dimetra (TETRA) communication system to develop availability probabilities for two- and three-shaft underground mine communication systems. Figure 9 graphically shows the availability simulation results for one-, two-, and three-shaft underground mine communication systems, separately and together. According to the results of the probabilities of these communication systems availability (shown in Table 3) the availability probability of the three-shaft underground mine communication system shows the highest result of 85.18%, compared to the availability probability results of the one- and two-shaft underground mine communication system. In other words, the probability of communication system availability after an average of 10 years of operation in underground mines is 81.26% for the one-shaft communication system, 62.38% for the two-shaft underground mine communication system or single-standby communication system, and the three-shaft showed results of 85.18% for an underground mine communication system or dual-standby communication system. Moreover, the three-shaft communication system can work with 100% availability probability for the first three years of operation. While the two-shaft underground mine communication system can work with 100% availability probability for the first two years in single-shaft underground mine communication systems or for communication systems without standby, the results show that it is possible to operate with 100% availability probability in the first year. For a three-shaft underground mine, according to Motorola Dimetra (TETRA) system specifications, each shaft has one core system, six base stations, one site link, one optical repeater and one optical cable management device, (a total of 3 core systems, 18 base stations, 3 site links, 3 optical repeaters and 3 optical cable management devices) which were modeled and developed for each shaft and for in general (Figure 9) (see Supplementary Materials). Figure 10 and Table 4 (see Supplementary Materials), on the other hand, shows the simulation results of combined corrective and preventative maintenance, results after corrective maintenance was doubled, and when preventative maintenance was increased by 50%. In the current situation, there is a single site link that has no recourse site link. According to the results shown in this graph, the current availability rate of the site link was 78.27%. When preventative maintenance was increased by 50%, the availability rate of the site link increased by 84.41% and by 6.14% compared to the status. After doubling corrective maintenance, the rate increased by 87.77% and by 9.5% compared to the status, and after combining preventative and corrective maintenance, availability increased by 91.5% and by 13.23% compared to the status. Simulations were developed for the existing and without standby communication system, after doubling corrective maintenance and a 50% increase in preventive maintenance, as well as combining both corrective and preventive maintenance. \begin{table}
\begin{tabular}{p{113.8 pt}} \hline \hline
**Availability Rate of the Communication System with One-, Two-, and Three-Shaft mine/years** \\ \hline
**Availability of communication system without standbyin one- shaft underground mine** \\ \hline
**Availability of one-, two-, and three-shaft underground mine** \\ \hline
**Availability of the communication system in two-, two-, and three-shaft underground mine** \\ \hline
**Availability of the communication system in three-shaft underground mine** \\ \hline \hline \end{tabular}
\end{table}