## 4 Experimental Details and Results for VLC Using Designed Lamp
Figure 8: (a) Schematic of digital switching network for DL (made by assembling seven colored LEDs on heat sink controlled using single mosfet) as a source of encoded information for VLC and p-i-n diode as a receiver at a distance of 1 m; (b) shows the process flow of the designed system. Duty cycle distortion like ISI can be caused by reflections or bandwidth limitations of the channel or receiver [58]. The DL is driven at 120 mA and WL at 90 mA to obtain 5 \(\upmu\)V current (rms) at the photodiode. Figure 10 shows the eye diagram and jitter of the received PRBS signals using WL and DL as transmitters while maintaining the same photocurrent output from the photodiode (5 \(\upmu\)A). The root-mean-square current was measured using a Fluke-115 multi-meter (Fluke Corporation PO Box 9090, Everett, WA 98206, USA). The eye diagram was constructed using a real-time (EXR054A, 500 MHz, 16 Gs/s, Keysight Technologies, Penang, Malasiya) oscilloscope at the sampling rate of 1 GSa/s at a memory depth of 10 million points. Here, note that an explicit clock signal of 1 kHz (Agilent 33521A Function Generator) is used. Figure 10a,b depicts the superimposed tracing of 1000-bit intervals. The eye pattern of the WL signal is noisy because of the edges' slow rising time. Conversely, the fast rise time of DL gives more noise margin (eye-opening), which may contribute to a lower ISI. Jitter strongly affects link reliability by deviating edges due to signal crosstalk frequencies, making clock recovery difficult [58; 59; 40]. The jitter analysis of TIE is carried out in this experiment at the rising and falling edge of the signal to check the flickering of a light source. Figure 10c shows that TJ is the convolution of RJ and DJ. From the signal itself, the clock is recovered using a software-based clock recovery method of Keysight (DSO60002A, 1 GHz, 20 GSa/s), which aligns the received PRBS data edges with the virtual clock edges. From Figure 10d,e, peak-to-peak (pp) jitter is less for DL (41 \(\upmu\)s) than that of WL (68 \(\upmu\)s). This jitter (pp) represents the deterministic component (DJ) present in the signal, which is some ambient modulation frequency or interference present in the signal. This DJ component can be used to guess the transmitted pattern. The RJ (considering the left peak only) is 1.1 \(\upmu\)s for DL, which was higher than that of WL (708 ns) because seven LEDs are modulated together; hence, random noise might have increased due to color crosstalk. From Equation (9), we calculated a TJ of 56 \(\upmu\)s for DL and 78 \(\upmu\)s for WL. Notably, the total jitter is 39% reduced using DL as an information source with simultaneous illumination. Table 1 indicates signal parameters such as extinction ratio, SNR, rise time, 3-dB bandwidth, DJ, RJ, TJ, and Q (quality) factor. The 3 dB bandwidth is \(1/\sqrt{2}\) times the maximum amplitude of the PRBS test signal without the dc component. Notably, WL has a mean rise time of 41 \(\upmu\)s, while DL  
Figure 9: The time delay between pseudo-random binary sequence (PRBS) input as a reference and received signal versus received power at the detector. Increased input power resulted in decreased time delay. has 28 \(\upmu\)s. Hence, DL reduced the rise time by 31%. Based on these findings, we can say that bandwidth efficiency or theoretical bit rate (from Equation (12)) is higher for DL as rise time is inversely related to bandwidth. A higher extinction ratio also signifies a lesser bit error rate. \begin{table}
\begin{tabular}{l l l} \hline \hline
**Evaluation Parameters** & **White LED** & **Designed Lamp** \\ \hline
3 dB bandwidth of a signal & 987 Hz & 994.6 Hz \\ Rise Time (avg) & 41 \(\upmu\)s & 28 \(\upmu\)s \\ Q factor & 55 & 60 \\ Extinction Ratio & 22.64 dB & 23.3 dB \\ SNR & 64.05 dB & 61.8 dB \\ Deterministic Jitter (DJ, peak to peak) & 68 \(\upmu\)s & 41 \(\upmu\)s \\ Random Jitter (RJ) & 708 ns & 1.1 \(\upmu\)s \\ Total Jitter (TJ) & 78 \(\upmu\)s & 56 \(\upmu\)s \\ \hline \hline \end{tabular}
\end{table}