# Utilization of an OLED-Based VLC System in Office, Corridor, and Semi-Open Corridor Environments
## 3 Results
### Channel Characteristics  
The channel gain \(H(0)\) defines the achievable SNR for a given incident power. To quantify the data rate, \(H(0)\) and the optical signal attenuation \(\mathrm{OPL}=-10\mathrm{log}_{10}(H(0))\) caused by reflections and transmission in the free space are obtained [21; 34]. The RMS delay spread is commonly used to define  
Figure 6: The bit-error-rate (BER) for flat and curved OLEDs at \(R_{b}\) of: (**a**) 4 Mb/s, and (**b**) 6 Mb/s for an office. the time dispersion along the propagation path. The channel mean excess delay \(\tau\) and the RMS delay spread \(\tau_{\text{RMS}}\) are given as [27; 31]. \[\tau =\frac{\int\limits_{0}^{\infty}t\times h(t)dt}{\int\limits_{0}^{ \infty}h(t)dt}, \tag{6}\] \[\tau_{RMS} =\sqrt{\frac{\int\limits_{0}^{\infty}(t-\tau)^{2}\times h(t)dt}{ \int\limits_{0}^{\infty}h(t)dt}}. \tag{7}\]  
Figure 7 depicts the \(\tau_{\text{RMS}}\) plot for the flat and curved OLEDs in an office. The angle \(\theta\) is shown in Figure 7 to identify the Rx's location on the semi-circular path with the radius \(d\). \(\tau_{\text{RMS}}\) increases with \(\theta\) reaching the maximum value of 5 and 10.7 ns at \(\theta\) of \(90^{\circ}\) for the curved and flat OLEDs, respectively. It is obvious that, for the curved OLED, there is a slight change in \(\tau_{\text{RMS}}\) by about 0.8 ns with respect to \(\theta\). However, \(\tau_{\text{RMS}}\) has changed about 7.3 ns for the flat OLED. Note, there is a significant increase in \(\tau_{\text{RMS}}\) for \(\theta>40^{\circ}\) for the flat OLED. Using a non-linear approximation algorithm for both cases, a two-term power series model can be derived from simulations for \(\tau_{\text{RMS}}\) as a function of \(\theta\) given by  
\[\tau_{\text{RMS}}=p_{1}\theta^{p_{2}}+p_{3}, \tag{8}\]  
where \(p_{1}\), \(p_{2}\) and \(p_{3}\) are summarized in Table 2. Note, the empirical parameters can vary based on the number of objects in the room and the size of the specified confined space. \begin{table}
\begin{tabular}{c c c c} \hline
**OLED Type** & \(\mathbf{p_{1}}\) & \(\mathbf{p_{2}}\) & \(\mathbf{p_{3}}\) \\ \hline Curved & \(8.707\times 10^{-10}\) & 4.589 & 4.172 \\ Flat & \(1.765\times 10^{-5}\) & 2.875 & 3.312 \\ \hline \end{tabular}
\end{table} 
Table 2: Numerical modeling parameters for \(\tau_{\text{RMS}}\) in the case of using flat and curved OLEDs in office. Figure 7: Comparison of a flat and curved OLEDs employed in the office in term of \(\tau_{\text{RMS}}\). Figure 8 shows the azimuthal dependence of the OPL distributions for flat and curved OLEDs for the proposed scenario in an office. OPL increases with \(\theta\) reaching a maximum of 60.4 and 70.2 dB at \(\theta\) of 90\({}^{\circ}\) for curved and flat OLEDs, respectively. Note, up to \(\sim\)14 dB drop in the channel gain can be seen for the flat OLED when \(\theta\) changes from 0\({}^{\circ}\) to 90\({}^{\circ}\), which is considerably higher compared with the reduced \(\sim\)2 dB channel gain for curved OLED. It can be seen that, for the flat OLED and \(\theta<30^{\circ}\) there is an improvement in OPL by \(\sim\)1.8 dB compared with the curved OLED. However, for \(\theta>45^{\circ}\), there is high received power enhancement for the curved OLED compared with the flat OLED, e.g., OPL penalties for flat OLED are 5 and 10 dB for \(\theta\) of 75\({}^{\circ}\) and 90\({}^{\circ}\), respectively. In addition, for both cases OPLs can be determined as the 2-term power series models as  
\[\text{OPL}=a_{1}\theta^{a_{2}}+a_{3}, \tag{9}\]  
where the derived parameters \(a_{1}\), \(a_{2}\) and \(a_{3}\) are shown in Table 3.  
Figures 9 and 10 illustrate the channel characteristics for both open and semi-open corridor when OLED are mounted on the inner shop wall behind the glass window and on the wall or shop window inside the corridor while the user is moving along the corridor in terms of OPL and \(\tau_{\text{RMS}}\). As can be seen, both OPL and \(\tau_{\text{RMS}}\) plots show symmetry about the center of the indoor environment with minimum values at the center.