## 5 Results and Analysis
### Received Power  
Signal power plays an important role in signal propagation and medium characteristics in which the signal is traveling between transceiver nodes. The critical characteristics of mines induce a negative impact on signal transmission resulting in low power reception. Evaluating signal power at the reception point is a basic approach to estimate the condition of data extraction from the received signal. The multimode model is implemented in this study to derive Equation (23) for received power in the particular room-and-pillar environment of the mine. The comparative analysis of the transmitted signal at 2.4 GHz and 5 GHz frequency is performed for the link distance of 500 m. Moreover, the received power response is examined by classifying LOS zones. Figure 6a shows the comparative analysis of received power between 2.4 GHz and 5 GHz. The received power is calculated at multiple frequencies and particularly the response is much better at 2.4 GHz as compared to 5 GHz. It depicts that the attenuating factor has a mild effect at lower frequencies of the UHF band in mines, which leads to better received power at the reception point. It can be seen that the power of the signal is declining exponentially at the beginning, but the received power response becomes linear with the rise of link distance. The major effect of attenuation on the propagated signal can be mitigated to some extent by the hike of transmission power. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameter** & **Symbol** & **Values** \\ \hline Transmitted Power & \(P_{T}\) & 13.97, 16.98, 18.75 dBm \\ Transmitter Gain & \(G_{T}\) & 2 dB \\ Receiver Gain & \(G_{R}\) & 2 dB \\ Operating frequency & \(f\) & 2.4 GHz–5 GHz \\ Link Distance & \(z\) & 0–500 m \\ Width of Mine gallery & \(w\) & 5 m \\ Height of Mine gallery & \(h\) & 4 m \\ Attenuation Coefficient & \(\alpha_{n}\) & 10–20 dB/m \\ Vertical walls permittivity & \(\varepsilon_{0}\) & 5 \(\varepsilon_{0}\) \\ Horizontal permittivity & \(\varepsilon_{h}\) & 4 \(\varepsilon_{0}\) \\ Wavelength & \(\lambda\) & 0.1249, 0.0599 m \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Particular and associate values used for simulations. Similarly, signal propagation analysis is taken in a mine's sub-gallery where the LOS path is broken and classified into LOS, NLOS, and partial line-of-sight (PLOS) segments. The received signal power is calculated for given LOS categories and the results are given in Figure 6. It can be observed from Figure 6 that there is a clear difference in the signal-received power. The received power for LOS is much higher than NLOS and PLOS links, and the response of the analysis concerning frequencies comparison is nearly constant throughout the link distance. The difference in signal power of PLOS and NLOS is not considerably high but for a clear LOS link, the performance of communication is much better. Performance analysis of received power is carried out using the experimental data to validate the theoretical received power, as shown in Figure 7. Long-range measurement is required to examine the characteristic behavior of EM-propagated signals in the environment of an underground mine. The experiments are taken at 2.4 GHz and 5 GHz frequency band in the mine gallery (coal mine, Xian, China) which has 600 m length, 5 m width and 4 m height. The mine contains mining equipment and infrastructure. The transmitters are mounted at multiple locations such as ceilings, walls, and in the center of the gallery at a  
Figure 5: Path-loss analysis, (**a**) Distance-based path loss, (**b**) Frequency-based path loss. Figure 6: (**a**) Received power comparison at 2.4 GHz and 5 GHz, (**b**) Received power analysis at 2 GHz–5 GHz band for LOS, NLOS and PLOS links. height of 3 m, 2.5 m, and 2 m, respectively. The receivers are oriented at the same height, and both transmitters and receivers are equipped with Omni-directional antennas (EM 6116). The antennas are vertically polarized and support the frequency band of 2 GHz to 5 GHz.