## 4 Result and Discussion
### Communication Performance
#### 4.2.1 Downlink Analysis  
_(a) Effects of Transmitter Locations on Received Power and SNR_  
The characteristics of a VLC channel are affected by the change in Tx and Rx locations, the reflectivity of the surfaces, as well as the room size, such that the same mobile terminal may incur different performances at different locations inside the indoor space. Accordingly, realizing evenly distributed \(SNR\) is important for ensuring the same commu \begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**Lamp Placement Scenario**} & \multicolumn{2}{c}{**Illuminance**} \\ \cline{2-3}  & **Uniformity** & **IQR (Lux)** \\ \hline CLQ & 0.377 & 295.82 \\ \hline CoIQ-10 & 0.688 & 70.59 \\ \hline CoIQ-9 & 0.659 & 111.23 \\ \hline CoIQ-4 & 0.688 & 109.43 \\ \hline CoIQ-3 & 0.762 & 75.37 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Performance Metrics for Illumination. nication performance without having a dead zone. Table 3 presents the average RMS delay spread, mean, and standard deviation of \(P_{r}\) and \(SNR\) for all the cases under consideration. The CoIQ-9 arrangement shows the least spread in \(P_{r}\) and \(SNR\), followed by CoIQ-10. However, CoIQ-4 experiences high deviation which is even higher than the conventional CLQ. Interestingly, CoIQ-3 is an exception here which, despite having the highest uniformity (see Table 2), exhibits high deviation. This shows that the number of luminaires and their placement plays a crucial role in determining the communication performance. Additionally, these results imply that high uniformity does not essentially guarantee least fluctuations in the \(SNR\). Therefore, a complete lamp layout analysis must be performed prior to installation when VLC is desired. The \(P_{r}\) and \(SNR\) plots for CLQ and CoIQ-9 configurations are illustrated in Figure 7. The \(P_{r}\) of CoIQ-9 is approximately restricted between 11 and 15.5 dBm with a variation of 4.5 dBm (Figure 7c) whereas the \(P_{r}\) of CLQ is spread over a wider range of \(\sim\) 8.5 dBm (Figure 7a). The higher spread in \(P_{r}\) of CLQ reflects in a high \(\sigma\) of 1.706 dBm, whereas \(\sigma\) in CoIQ-9 has reduced to almost half the value of CLQ, as summarized in Table 3. Because \(SNR\) follows the same profile as \(P_{r}\), the proportionality of reduced fluctuations in \(P_{r}\) is also evident in \(SNR\). For example, the \(SNR\) for CLQ is spread over \(\sim\) 7.5 dB range (between 31.65 dB to 39.17 dB), whereas the \(SNR\) for CoIQ-9 varies over \(\sim\)3.3 dB range (between 33.42 to 36.74 dB) (see Table 3). This implies that the \(SNR\) range in CoIQ-9 reduces by almost 50%. The contour plot of CLQ shown in Figure 7b also shows that \(SNR\) is the highest at the center (\(\sim\) 39 dB) and tends to drop continuously by \(\sim\)1 dB for every 0.5 m away from the centre. The \(SNR\) plot for CoIQ-9 depicted in Figure 7d illustrates that the highest \(SNR\) value of \(\sim\) 36.5 dB only covers a smaller area and the majority areas have \(SNR\) between 33.5-35.5 dB, implying that the \(SNR\) is more evenly spread in CoIQ-9 than in CLQ. This is also evident from Table 3, which indicates that \(\sigma\) of \(SNR\) reduces from 1.48 in CLQ to 0.678 in CoIQ-9, i.e. a reduction of \(\sim\)54.18% in the latter. Because the rearrangement of transmitters optimizes the uniformity of illuminance by 74% and reduces the fluctuations in \(SNR\) by 54% in CoIQ-9, it can be inferred that the locations of transmitters play a key role in determining the overall system performance. Moreover, the least \(SNR\) value is well above 15.6 dB, which is the minimum required to ensure a BER of \(10^{-9}\).