## 5 Simulation Results and Discussions
### Effects of Different Ambient Light Sources  
In the results above, the effects of two ambient noise sources (fluorescent lamps and dimmable LEDs) on the performance of the VLC systems were analyzed. This subsection examines the impact of noise generated by each source individually on the BER performance of the MIMO-VLC system using the QPSK technique. To accurately evaluate the effect of ambient light interference on system performance, quantitative values for background light noise sources were incorporated into the simulation. Two typical ambient light sources were modeled: a fluorescent lamp and a dimmable LED, each contributing distinct interference characteristics. The optical noise power received at the photodiode from the fluorescent lamp was approximately 0.2 \(\upmu\)W, corresponding to typical indoor lighting conditions (\(\sim\)500 lux). The dimmable LED introduced a stronger interference level of around 0.5 \(\upmu\)W, reflecting brighter environments (\(\sim\)1000 lux) and accounting for pulse-width modulation flicker [15]. When both sources were active simultaneously, the total ambient noise power reached approximately 0.7 \(\upmu\)W. These power levels were incorporated into the shot noise model using Equation (6), with the help of a photodetector responsivity \(R=0.6\) A/W and receiver bandwidth \(B=1\) GHz, to simulate realistic interference levels in the MIMO-VLC system. Figure 13: BER performance comparison for the MIMO–VLC system with and without ambient noises. As shown in Figure 16, the noise from the dimmable LED has a greater effect on BER performance compared to that from the fluorescent lamp. For instance, at a log(BER) of  
Figure 14: Received power comparison for the SISO–VLC system with and without ambient noise. Figure 15: Received power comparison for the MIMO–VLC system with and without ambient noise. \(-50\) dB, the coverage distance decreases from 9.3 m to 4.6 m, representing a 50.5% reduction when both noise sources are considered. However, when only the dimmable LED noise is considered, the coverage distance decreases from 9.3 m to 5.8 m, a reduction of 37.6%. Similarly, the noise from the fluorescent lamp alone reduces the coverage distance from 9.3 m to 6.2 m, corresponding to a 33.3% reduction. This greater impact of dimmable LED noise is due to the larger number of interference noise components, as illustrated by the radio frequency (RF) spectrum in Figure 17[15]. This figure illustrates the RF spectrum of ambient light interference generated by both the fluorescent lamp and the dimmable LED. The dimmable LED shows a denser and more complex spectral profile, contributing more high-frequency noise components compared to the fluorescent lamp. These additional noise components increase the system's susceptibility to interference when dimmable LEDs are present, particularly in higher data rate modulation schemes like QPSK. To validate the effectiveness of the presented MIMO-VLC system in realistic VLC environments, we compared it with the findings presented by [PERSON] [15]. Figure 18 presents  
Figure 16: BER performance of the MIMO-VLC system using the QPSK technique under various ambient noise sources. Figure 17: The RF spectrum of fluorescent lamps and dimmable LED light sources. the BER performance as a function of ambient light power (dBm) under different lighting conditions, including fluorescent lamps and dimmable white LEDs. It can be observed that across all lighting scenarios, the presented MIMO-VLC system consistently achieves a lower BER under increasing ambient light power, demonstrating a clear improvement in system robustness. Notably, for combined fluorescent and LED interference at -6 dBm, the MIMO-VLC system achieves a BER below \(10^{-4}\), while the Y. Won [15] suffers significant performance degradation. Figure 19 presents a comparison of the achievable data transmission rates for the considered modulation schemes under both SISO and MIMO configurations.