# A New Internet of Things Hybrid VLC/RF System for m-Health in an Underground Mining Industry
## 5 Results and Discussion  
The parameters used in the simulations are summarized in Tables 2 and 3 the dimensions of the tunnel of (10 m, 5 m, 5 m) were obtained from [37]. The characteristics of both the photodetectors and the LEDs, in the visible and infrared range, were obtained from different technical sheets of commercial devices. As shown in Figure 7, the performance of the proposed system in the downlink using the LEDs placed on the ceiling of the underground tunnel and the photodetector placed on the miner's helmet is depicted to visualize the concept of proposed cells. Clearly, lobes that maximize power in the center of the cells and attenuate in the outer parts of the same can be distinguished. This result agrees with the expected behavior of the system, since the LED and photodetectors are sensitive to the presence of an object in the tunnel and their location in the scenario. This result is also in agreement with the results obtained in [37]. Furthermore, it is possible to observe that although the power received decreases in certain parts of the underground tunnel, it is never completely lost. Therefore, signal reception is ensured throughout the environment. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Component** & **Description** & **Variable** & **Value** \\ \hline \multirow{2}{*}{VLC Transmitter} & Power transmitted & \(Pt_{i}\) & 10 W \\  & Half Power Angle & \(cos\theta_{\frac{1}{2}}\) & 60\({}^{\circ}\) \\ \hline \multirow{4}{*}{VLC Receiver} & Physical surface area & \(A_{t}\) & 1 cm\({}^{2}\) \\  & Gain of the optical filter & \(T_{s}(\Psi)\) & 1 \\ \cline{1-1}  & Refractive Index & \(n\) & 1.5 \\ \cline{1-1}  & Field of View & \(\Psi_{c}\) & 60\({}^{\circ}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Simulation parameters for VLC downlink. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Component** & **Description** & **Variable** & **Value** \\ \hline \multirow{2}{*}{RF system} & Center Frequency & \(f\) & 868 MHz \\  & Path loss exponent & \(n\) & 2.2 \\ \hline \multirow{2}{*}{RF Transmitter} & Power transmitted & \(Pt_{RF}\) & 10 dBm \\  & Antenna gain & \(G_{t}\) & 2.5 dBi \\ \hline \multirow{2}{*}{RF Receiver} & Minimum power received (Sensitivity) & \(Pr_{RF}\) & \(-100\) dBm \\  & Antenna gain & \(G_{r}\) & 2.5 dBi \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Simulation parameters for RF uplink. Figure 8 presents the profile of the power received for the VLC downlink LOS. The graph depicts the relationship between distance and received power, showing how received power changes as the distance between the LED transmitters and the photodetectors on the safety helmets of mining personnel varies. This information is crucial to understanding the signal strength and coverage of the VLC downlink communication system in the mining environment. The received power for the VLC downlink LOS is determined by various factors such as the physical area of the photodetector, the distance between the LED and the photodetector, the gain of the optical filter, the width of the field of vision of the photodetector, and the Lambertian emission order. Understanding this profile is essential to optimize the placement of LED transmitters and photodetectors to ensure reliable and efficient communication within the mining environment. This analysis is important to evaluate the feasibility and effectiveness of the proposed hybrid architecture for VLC and RF communications in the context of mobile health monitoring of workers in the mining industry. By examining the profile of the power received for the VLC downlink LOS, researchers and industry professionals can make informed decisions regarding the implementation and deployment of the communication system. Table 3 presents the simulation parameters for the RF uplink in the proposed hybrid communication system for mobile health monitoring in the mining industry. The RF system  
Figure 8: Profile of received power for VLC downlink LOS. Figure 7: Optical power distribution for Cell ID LOS.