## 4 Result and Discussion
### Communication Performance
#### 4.2.2 Uplink Performance  
Having established in the previous section that the proposed-CoIQ placement technique outperforms CLQ from the illuminance as well as communication perspective, we now elaborate on how POR can be used to optimize the UL \(SNR\) uniformity. The principle assumes that, for a given set of parameters, the \(P_{r}\) and \(SNR\) obtained when moving from point A \(\rightarrow\) B in a linear channel will remain the same at the corresponding points if the transmitting and receiving devices are switched and direction of propagation is reversed, i.e., B \(\rightarrow\) A. To illustrate this, standalone DL and UL \(SNR\) distributions were obtained via simulations for a simple one transmitter and one receiver scenario. For DL, the Tx was positioned on the ceiling at the center of the room with coordinates (0, 0, \(L_{z}/2\)), whereas the receiver was located along the XY-plane at a height of 0.85m. The \(SNR\) was calculated for 1089 different positions (see Figure 10a) and the deviation that was obtained for this arrangement was 3.44 dB (this high value can be attributed to the presence of only a single transmitter). On the other hand, Figure 10b shows the result for UL \(SNR\) when the transmitter and receiver positions were switched and the direction of propagation was reversed. The \(SNR\) deviation for UL was also found to be 3.44 dB. Moreover, the values at corresponding locations in the room are also similar, as illustrated in Figure 10a,b. Hence, if DL simulations were to be carried out individually for \(TP_{1}\to RP\), \(TP_{2}\to RP\), \(TP_{3}\to RP\), \(TP_{4}\to RP\), and \(TP_{5}\to RP\), and super imposed, then the results obtained at corresponding points for \(RP_{1}\gets TP\), \(RP_{2}\gets TP\), \(RP_{3}\gets TP\), \(RP_{4}\gets TP\), and \(RP_{5}\gets TP\) would be the same. However, in a real scenario, the transmitters and receivers in UL may operate at different wavelengths (IR) and low transmit power values when compared to the DL (VLC) transceivers. Hence, UL analysis was performed with the transmit power and IR receiver responsivity values altered to 90 mW and 1A/W, respectively, in order to validate the practical application of reciprocity to our work. Additionally, the effect of \(\rho\) was considered, as the IR reflectivity is generally higher than that of VLC [36]. Table 6 summarizes the effect of each of these quantities on the UL \(SNR\) uniformities in terms of \(\sigma\) obtained for a typical hospital room size of 6.6 \(\times\) 6.6 \(\times\) 3 m\({}^{3}\), as presented in [27]. It can be observed \begin{table}
\begin{tabular}{c c c} \hline \hline  & \multicolumn{3}{c}{**Outage Area**} \\  & & **(\%)** \\ \hline
**Room size** & & \\
**(m\({}^{3}\))** & **CLQ** & **CoIQ** \\ \hline
5 \(\times\) 5 \(\times\) 3 & 0.08 & 0 \\ \hline
5.5 \(\times\) 5.5 \(\times\) 3 & 2.72 & 0.56 \\ \hline
6 \(\times\) 6 \(\times\) 3 & 10.68 & 4.52 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Percentage Outage Areas for CLQ and CoIQ. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & \multicolumn{3}{c}{**CLQ**} & \multicolumn{3}{c}{**Proposed-CoIQ**} \\ \cline{2-9}
**Room Size** & & & **Average** & & & \\
**(m\({}^{3}\))** & **Uniformity** & **Deviation in SNR** & **Average** & **Achievable** & **Uniformity** & **Deviation in SNR** & **Average** & **Achievable** \\
**(dB)** & **(dB)** & **(ms)** & **Data Rates** & **(Mbps)** & **(dB)** & **(ms)** & **Data Rates** \\ \hline
2.5 \(\times\) 2.5 \(\times\) 3 & 0.7111 & 0.8476 & 3.30 & 30.30 & 0.8612 & 0.6792 & 3.57 & 28.011 \\ \hline
4 \(\times\) 4 \(\times\) 3 & 0.5209 & 1.2240 & 5.38 & 18.58 & 0.8273 & 0.5962 & 5.34 & 18.72 \\ \hline
6.6 \(\times\) 6.6 \(\times\) 3 & 0.3329 & 1.8730 & 8.64 & 11.57 & 0.5370 & 1.1154 & 7.04 & 14.20 \\ \hline
7 \(\times\) 7 \(\timesthat \(\sigma_{UL}\) is similar to the corresponding \(\sigma_{DL}\) values for \(P_{t}\) and \(\gamma\) (see Table 5), whereas the deviations are further reduced when the reflectivity is increased.