# The Utilization of Artificial Neural Network Equalizer in Optical Camera Communications +
## 5 Results and Discussion
An example of transmitted and received signals with and without equalizer for \(N_{\text{pps}}\) of 8.7 pixels per symbol is illustrated in Figure 9. The equalized signal at the Rx side shows a significant improvement in reducing the impact of the ISI on the received signal with minimal signal distortions. The eye linearity of the received signals is measured based on the average amplitude levels is given by [39]:  
\[\text{Eye linearity}=\frac{\min\bigl{(}V_{\text{up}},\ V_{\text{mid}},\ V_{ \text{low}}\bigr{)}}{\max\bigl{(}V_{\text{up}},\ V_{\text{mid}},\ V_{\text{ low}}\bigr{)}}\, \tag{15}\]  
where \(V_{\text{up}},\ V_{\text{mid}},\ V_{\text{low}}\) and \(V_{\text{low}}\) are the average amplitude levels. Figure 10 shows the eye linearity of the received signals with respect to \(N_{\text{pps}}\) for the link with and without ANN equalizer and for \(T_{\text{exp}}\) of 2 ms. Note, we have used \(N_{\text{pps}}\), i.e., new terminology for a fair comparison considering the progress made in the development of ISs. As shown, for the link with no equalizer, the eye linearity increases with \(N_{\text{pps}}\) reaching a maximum level of 0.6 at \(N_{\text{pps}}\) of \(\sim\)26, beyond which it drops linearly with rapidly \(N_{\text{pps}}\). However, with the ANN equalizer, the eye linearity is improved significantly for both the test and trained cases reaching the optimal linearization of almost 1 at \(N_{\text{pps}}\) of 18  
Figure 8: Examples of the captured eye diagrams of the CIS received signal for CP 4-PAM with \(f_{\text{Tx}}\) of: (**a**) 220 Hz, (**b**) 320 Hz, (**c**) 420 Hz, (**d**) 520 Hz, (**e**) 1120 Hz, and (**f**) 1520 Hz. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Payload** & **Total Number of** & **Number of Row Pixels/** & \multirow{2}{*}{\(f_{\text{Tx}}\) **(Hz)**} \\
**Symbol/Packet (\(P_{\text{bil}}\))** & **Symbols/Packet** & **Symbol (\(N_{\text{pps}}\))** & \\ \hline
5 & 11 & 60.54 & 220 \\
10 & 16 & 41.62 & 320 \\
15 & 21 & 31.71 & 420 \\
20 & 26 & 25.61 & 520 \\
30 & 36 & 18.50 & 720 \\
35 & 41 & 16.24 & 820 \\
40 & 46 & 14.48 & 920 \\
50 & 56 & 11.89 & 1120 \\
70 & 76 & 8.76 & 1520 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Results with \(R_{\text{f}}\) of 30 fps and CIS width of 1024 px. and remaining constant beyond \(N_{\text{pps}}\) > 18 (i.e., being independent of \(N_{\text{pps}}\)). Thus, the ANN equalizer show an improvement of -66% in the eye linearity for \(N_{\text{pps}}\) > 18 pixels/symbol (i.e., \(f_{\text{Tx}}\) < 920 Hz) for both training and testing sets. Figure 10: The eye linearity against \(N_{\text{pps}}\) for the proposed system with and without equalization and for \(T_{\text{exp}}\) of 2 ms.  
Figure 9: An example of the transmitted and received signal with and without equalization for CP 4-PAM and \(N_{\text{pps}}\) of 18.5 row pixels/symbol: (**a**) training sets, and (**b**) testing sets. Next, we measured the BER as a function of \(N_{\text{pps}}\) for the link with and without ANN equalizer, as illustrated in Figure 11. In addition, shown is the forward error correction (FEC) BER limit line of \(3.8\times 10^{-3}\). Note, at the FEC limit the \(N_{\text{pps}}\) value is reduced from 30 to 20 for pixels per symbol for the links without and with the ANN equalizer, respectively, compared with the test plot. Thus, the effective \(R_{b}\) (i.e., no post- and pre-ambles) is estimated by:  
\[R_{b}=2\frac{V}{N_{\text{pps}}}.R_{f}\, \tag{16}\]  
where \(V\) represents the pixel row. The effective \(R_{b}\) at the FEC limit for the case with and without the ANN equalizer with a range of IS resolutions is indicated in Table 4. It demonstrates with the ANN equalizer \(R_{b}\) of 24.4 and 12.2 kbps for \(R_{f}\) of 60, and 30 fps, respectively, can be achieved compared with the case of no equalizer with \(R_{b}\) of 18.6, and 9.3 kbps for \(R_{f}\) of 60, and 30 fps, respectively.