## 2 Materials and Methods
### Definition and Design of the System's Components
#### 2.2.1 LED Driver
\begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline \multicolumn{2}{c}{**Input**} & \multicolumn{2}{c}{**Equalizer 1**} & \multicolumn{2}{c}{**Amplification Stage 1**} & \multicolumn{2}{c}{**Equalizer 2**} & \multicolumn{2}{c}{**Amplification Stage 2**} & \multicolumn{2}{c}{**Current Source**} \\ \hline R\({}_{5}\) & 200 \(\Omega\) & R\({}_{1}\) & 3.9 k\(\Omega\) & R\({}_{6}\) & 20 k\(\Omega\) & R\({}_{3}\) & 1 k\(\Omega\) & R\({}_{0}\) & 1 k\(\Omega\) & R\({}_{33}\) & 10.7 k\(\Omega\) \\ C\({}_{3}\) & 1 pF & C\({}_{1}\) & 22 pF & R\({}^{7}\) & 1 k\(\Omega\) & C\({}_{2}\) & 25 pF & R\({}_{11}\) & 12 k\(\Omega\) & R\({}_{14}\) & 5 k\(\Omega\) \\ V\({}_{\rm m}\)(AC) & 0.8V\({}_{\rm pe}\) & R\({}_{2}\) & 1 k\(\Omega\) & R\({}_{5}\) & 500 \(\Omega\) & R\({}_{4}\) & 50\(\Omega\) & R\({}_{2}\) & 1 k\(\Omega\) & R\({}_{5}\) & 5.5 \(\Omega\) \\ V\({}_{\rm m}\)(DC) & 0 V\({}^{\rm T}\) & & & C\({}_{4}\) & 56 nF & C\({}_{6}\) & 56 nF & C\({}_{6}\) & 56 nF & TRT & TN011 ON3 \\  & & & & Ampl & LTC6268-10 & & Ampl & LTC6268-10 & V\({}_{\rm ad}\) & 12 V \\  & & & & R\({}_{9}\) & 200 \(\Omega\) & & & & & \\  & & & C\({}_{5}\) & not mounted & & & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Components of the LED driver. Figure 6: Phase-advance equalizer implemented for (**a**) the first stage for a pole located at 1.8 MHz, and (**b**) the second stage for a pole located at 9 MHz. Figure 7: LED driver implemented with 2 equalization and 2 amplification stages. The simulation results of this circuit are demonstrated in Figure 8, which reveal the frequency response of the LED driver with two equalization and two amplification stages. The circuit attained a \(-3\) dB cut-off frequency of roughly 29 MHz. The frequency and phase response of the visible optical channel were measured using a Moku frequency response analyzer [27]. This device enables the measurement of both the module and phase of the optical channel's frequency response. The analyzer operates by sweeping a sinusoidal signal across an adjustable frequency range from 10 mHz to 20 MHz, and it can apply a DC bias of up to \(\pm 5\) V.  
The measurement set-up involved positioning the LUW-CN7N-KYLX-EMKM OSCRAM LED and the Thorlabs PDA10A2 PD [28] at a distance of 9 cm without any lens on the Thorlabs PDA10A2 PD (as depicted in Figure 9a). The measurement was performed under an illuminance of 30,000 lx on the Thorlabs PDA10A2 PD, with the illumination level measured using a MAVOLUX 5032C USB luxmeter [29], manufactured by Gossen and bought on [[https://www.pce-iberica.es/medidor-detalles-tecnicos/instrumento-de-radiacion/luxometro-mavolux.htm](https://www.pce-iberica.es/medidor-detalles-tecnicos/instrumento-de-radiacion/luxometro-mavolux.htm)]([https://www.pce-iberica.es/medidor-detalles-tecnicos/instrumento-de-radiacion/luxometro-mavolux.htm](https://www.pce-iberica.es/medidor-detalles-tecnicos/instrumento-de-radiacion/luxometro-mavolux.htm)) (accessed on 5 September 2024). The measured frequency response, which includes both the magnitude and phase, is illustrated in Figure 9b. The bandwidth achieved by the LUW-CN7N-KYLX-EMKM OSRAM LED and its LED driver based on 2 equalization and 2 amplification stages was 14.45 MHz, which complies with the 10 MHz requirement of the VLC channel. For the IR uplink, the IR HSDL-4250 LED [30] was selected, which is a high-power Aluminum Gallium Arsenide (AlGaAs) LED. This IR LED was manufactured by Avago and bought on [[https://mouser.com/](https://mouser.com/)]([https://mouser.com/](https://mouser.com/)) (accessed on 5 September 2024). It is optimized for high-speed IR communications and efficiency at emission wavelengths of 870 nm and presents a radiant on-axis intensity of 180 \(\frac{\mathrm{mW}}{\mathrm{sr}}\). The measured bandwidth of the IR HSDL-4250 LED reached 2 MHz. Given this, the previously mentioned LED driver, encompassing 2 equalization and 2 amplification stages, was utilized for the uplink.