# Simulation of an Indoor Visible Light Communication System Using Optisystem
## 6 Results and Discussion  
We started our simulation by considering the LOS and NLOS propagation models from Figures 2, 4 and 6. The Optisystem simulation results from these propagation models are shown in Figures 11-13. The propagation model uses a square pulse as its input. The oscilloscope visualizer from the transmitter side shows the generated input signal. The oscilloscope visualizer_1 indicates the signal from the receiver. These results indicate the input signal shape is distorted from the diffuse channel and the reflection paths. The width and amplitude of the transmitted signals are changed when it arrives at the receiver side. When considering the received signal amplitude, the LOS propagation model's receiver affected negligible amplitude distortions compared to NLOS propagation models. The NLOS propagation model results show channel interference's effect when the system has multiple reflection paths. When the system considers the various numbers of reflection points from the walls, the received signal is distorted and affects the VLC system's performance. When we see the smoothness of the received signal, the single LED NLOS propagation-based approach has smooth curvature signals compared to the dual LED-based VLC system. The signal amplitudes in both (single and dual LED) methods are almost similar, indicating that the signal amplitude distortion effects in the single LED-based approach can be overcome by adding another LED into the VLC system. These results give the signal shape (amplitude variation) analysis from the receiver side. In addition, it is necessary to investigate the receiver's signal distortions for further validation of the VLC systems. We consider the eye diagram of the received signal in LOS and NLOS propagation models to validate our simulation results. Figure 14 shows the eyes diagram results from our simulation. Figure 11: Simulation results from LOS propagation model. (**a**) Input signal. (**b**) Output signal. From Figure 14, the eye diagram results indicate the signal distortion level in LOS and LOS propagation models. The results show that the LOS propagation model (Figure 14a is more precise than other models and has good eye-opening results. The single LED NLOS propagation model (Figure 14b) has higher signal distortion, drastically disturbing the eye-opening. The improper eye-opening results of the single LED propagation model indicate that the system failed to transmit the data correctly. The reflection paths in the simulation environment increase the data loss, affecting the VLC performance. To enhance the performance of the single LED NLOS propagation model-based approach, the simulation considers an additional LED which reduces the signal distortion. The dual LED  
Figure 12: Simulation results from a single LED NLOS propagation model. (**a**) Input signal. (**b**) Output signal. Figure 13: Simulation results from a dual LED NLOS propagation model. (**a**) Input signal. (**b**) Output signal. NLOS propagation model-based approach (Figure 14c) has good eye-opening results than the single LED-based approach. This indicates that adding extra LEDs in the VLC system can improve the data loss issue in a VLC system. However, the addition of LEDs increases the system's complexity. The system requires high-speed switching electronics and high-speed LEDs and phototransistors, giving high system costs for real-time implementation. Furthermore, we also analyzed the effect of incident (\(\theta_{d}\)) and irradiance (\(\theta_{s}\)) angles in an LOS propagation model. We started our simulation by setting the angle of the incident (\(\theta_{d}\)) to a constant value (30\({}^{\circ}\)) and changed the irradiance angle from 0\({}^{\circ}\) to 50\({}^{\circ}\). Similarly, we kept the angle of irradiance at a constant value (30\({}^{\circ}\)) and changed the incident angle from 0\({}^{\circ}\) to 50\({}^{\circ}\). Figures 15-18 show the oscilloscope visualizer_1 results from the receiver. These results indicate the effect of irradiance and incident angles in an LOS propagation model.