## 4 Result and Discussion
### Communication Performance
#### 4.2.1 Downlink Analysis
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & & & & \multicolumn{4}{c}{**Communication**} \\ \cline{3-8}  & & & & **Received Power** & & **SNR** \\
**Lamp** & **RMS Delay Spread** & & & **(dBm)** & & **(dB)** \\ \cline{2-8}
**Placement** & **Average** & **Average** & & & **Standard** & **Min** & **Max** & **Standard** \\
**Scenario** & **\(\mathbf{D_{rms}}\)** & **Achievable** & & & **Deviation** & **Min** & **Max** & **Deviation** \\  & **(ns)** & **Bitrates** & & & & & & \\ \hline CLQ & 5.76 & 17.36 & 16.00 & 1.71 & 31.65 & 39.17 & 1.48 \\ \hline CoIQ-10 & 5.44 & 18.38 & 13.68 & 0.92 & 32.43 & 35.93 & 0.80 \\ \hline CoIQ-9 & 5.63 & 17.79 & 14.70 & 0.78 & 33.42 & 36.74 & 0.68 \\ \hline CoIQ-4 & 5.00 & 20.00 & 10.12 & 1.99 & 28.57 & 34.71 & 1.74 \\ \hline CoIQ-3 & 5.56 & 17.98 & 11.62 & 1.38 & 30.52 & 34.94 & 1.20 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Performance Metrics for Communication. _(b) Effects of Transmitter Locations on RMS Delay Spread_  
Figure 8 illustrates the \(D_{rms}\) plots for CLQ and CoIQ-9 with values distributed symmetrically along the XY-receiving plane due to the square room geometry. For CLQ, the \(D_{rms}\) values are lowest around the center of the room (Figure 8a). This is because all of these points are equidistant from the reflecting walls and the source, so that the difference in their traced path lengths is not very high. The maximum \(D_{rms}\) value of \(\sim 6.5\) ns is present at the corner of the room, where this increase is attributed to large differences between LoS and reflecting paths from walls. For the CoIQ-9 arrangement (Figure 8b), \(D_{rms}\) values are lowest at the center, moderate under each transmitter position and the edges, and maximum (\(\sim 7\) ns) at other positions. Moreover, the average \(D_{rms}\) is slightly lesser in CoIQ than in CLQ, with the values being \(5.63\) and \(5.76\) ns, respectively (see Table 3), due to which CoIQ has slightly better achievable data rates. Figure 7: Received power for (**a**) CLQ (**c**) CoIQ-9 with respective SNR contours in (**b,d**). (c) Effects of Varying Body Postures under Low-Lightting Conditions  
All of the aforementioned results were based on the transmit power derived from a luminous intensity of 0.73 red, which produced high average illuminance levels of about 500 lux. However, in this section, we study the effect of low-lighting conditions on \(SNR\) distribution for standing, sitting, and sleeping positions when the average illuminance remains under 100 lux (required for sleeping scenarios). Figure 9 shows the histograms that were obtained for \(SNR\) at 10,000 different locations on the XY-receiving plane for all three postures. It can be observed that ColQ has lesser spread in \(SNR\) than CLQ in all three scenarios. Moreover, the \(SNR_{min}\) value for ColQ for all the postures is approximately 16.5 dB which is sufficient to maintain a BER of \(10^{-9}\), given that the threshold is 15.6 dB. On the contrary, CLQ offers \(SNR_{min}\) of 15 dB, which does not ensure the minimum BER performance. This implies that, during low-lighting conditions, the user in CLQ may experience communication dips at several points in the room. Besides, we also determined the outage areas to further gauge the performance under low-lighting conditions, i.e., the regions where the \(SNR\) falls below the threshold level of 15.6 dB. The results have been summarized in Table 4 for various room dimensions. The outage area increases with the increasing room dimensions for both the configurations; however, the proposed-ColQ technique will always have a lower outage area than CLQ. Based on these results and  
Figure 8: Root mean square (RMS) delay spread distribution for (**a**) CLQ and (**b**) ColQ-9. observations, it can be inferred that CoIQ will always achieve better illumination uniformity and lesser fluctuations in \(SNR\) when compared to the conventional CLQ scheme.