# The Utilization of Artificial Neural Network Equalizer in Optical Camera Communications +
## 5 Results and Discussion  
The experimental work was focused on deploying an MLP-based equalization to mitigate the ISI due to the limited modulation bandwidth of the CMOS IS-based Rx. The measured and simulated CIS for \(T_{\text{exp}}\) of 2 ms are highlighted in Figure 6, showing that the obtained IS bandwidth (i.e., a 3 dB point) was 250 Hz. It is also noted that the mismatch between the measured and simulated response was caused by aliasing due to the limited sampling frequency of the IS and utilization of image compression techniques [38]. The CP 4-PAM encoded signal was then generated at a different bandwidth \(f_{\text{Tx}}\) of up to 1520 Hz. \begin{table}
\begin{tabular}{c l l} \hline \hline  & **Description** & \multicolumn{1}{c}{**Value**} \\ \hline \multirow{4}{*}{**Tx**} & LED type & \multicolumn{1}{c}{Luxeon Rebel LED (SR-01-WC310)} \\  & Tx signal bandwidth & \(f_{\text{Tx}}\) (Hz) & 220–1520 Hz \\  & Tx bias current & & 180 mA \\ \hline \multirow{4}{*}{**Camera Rx**} & Camera model & Thorlabs DCC1645C-HQ \\  & Exposure time \(T_{\text{exp}}\) & 2 ms \\  & Maximum SNR of IS & 44 dB [37] \\  & Lens type & Navitar 12 mm F/1.8 2/3” 10 MP \\  & Pixel clock & 10 MHz \\  & Camera raw image resolution & 1280 \(\times\) 1024 pixels \\  & Captured symbols per frame & 11–76 symbols \\ \hline \multirow{4}{*}{**Packet Generator**} & Data format & CP-PAM \\  & Symbol per packet \(P_{\text{bit}}\) & 5–70 symbols \\ \cline{1-1}  & Packet generator sample rate & 11.125 kHz \\ \cline{1-1}  & Number of samples \(n_{\text{samp}}\) & 10 \\ \hline \multirow{2}{*}{**Channel**} & Channel length & 50 cm \\ \hline \multirow{4}{*}{**ANN Equalizer**} & Activation function & Hyperbolic tangent sigmoid \\  & Number of neurons in input layer & 200 \\ \cline{1-1}  & Number of neurons in output layer & 1 \\ \cline{1-1}  & Number of neurons in hidden layer & 200 \\ \cline{1-1}  & Number of hidden layers & 2 \\ \cline{1-1}  & Percentage of the train to test & 0.8 \\ \cline{1-1}  & Maximum epochs & 1000 \\ \cline{1-1}  & learning rate parameter \(\eta\) & 0.01 \\ \cline{1-1}  & Network training function & Resilient back-propagation \\ \hline \hline \end{tabular}
\end{table} 
Table 2: System parameters. Figure 6: Measured and estimated bandwidth of the for IS with \(T_{\text{exp}}\) of 2 ms. The captured frames at the Rx are processed with \(P_{\text{bit}}\) of up to 70 symbols per packet. Figure 7 illustrates examples of the captured frames and the processed signals for \(P_{\text{bit}}\) of 5, 10, 15, 20, 50, and 70, i.e., \(f_{\text{Tx}}\) 220, 320, 420, 520, 1120, and 1520 Hz, respectively. Note, the width of the received Qth packet and the recorded \(F_{s}\) are 666 pixels and 13.31 kHz, respectively, based on the demodulated signal, see Figure 7. Increasing \(f_{\text{Tx}}\) decreases the number of received pixels for each CP 4-PAM symbol, thus, reducing the quality of data transmission. The number of pixels utilized for each CP 4-PAM symbol is indicated in Table 3. For the link with the ANN-based equalizer deployed at the Rx side, the quality of the received signal was measured using the eye diagrams and the BER performance. As illustrated in the eye diagrams, see Figure 8, the eye-openings indicate the impact of the ISI on the received signal. Note, (_i_) the threshold levels can be differentiated for \(P_{\text{bit}}\) of 5 and 20 symbols, see Figure 8a,b, respectively, but not for \(P_{\text{bit}}\) of 50 and 70 symbols as in see Figure 8c,d, respectively; (_ii_) the five levels are shown in the eye diagrams, where one of the levels represents the packet overhead designed to maintain the same average power for CP 4-PAM; and (_iii_) the overhead level is removed at the Rx side using Algorithm 1. Figure 7: Examples of the frame acquisition based on CIS for CP 4-PAM and \(f_{\text{Tx}}\) of: (**a**) 220 Hz, (**b**) 320 Hz, (**c**) 420 Hz, (**d**) 520 Hz, (**e**) 1120 Hz, and (**f**) 1520 Hz.