# Adaptive Software Defined Equalization Techniques for Indoor Visible Light Communication
## 6 Measurements
### Configuration, Scenario, and Results  
The following configuration was used during the measurements: a carrier frequency of 3 MHz with a variable bandwidth from 1 MHz to 4 MHz. However, since NI USRPs had some channel widths fixed, it used a slightly wider channels (for example 3.0303 MHz instead of 3 MHz). The number of transmitted symbols was 10,000. The measurement itself was carried out in the laboratory of the Technical University of Ostrava. The Philips Fortimo ceiling light was mounted on a moveable holder, which could be freely adjusted on a custom ceiling rail system. This type of light was chosen based on the statistics from Czech public institutions. It is often used in the construction of new buildings or during renovations of older ones. Since it was also used in the university corridors, the whole system could be beta tested directly during full operation. The selected parameters of this light source can be seen in Table 2.  
The receiving photodetector was mounted on a movable laboratory cart. Therefore, it was possible to change the position of the detector, but always keeping the same height. This scenario can be seen in Figure 11. The Philips light source illuminated conical area with diameter of 700 cm. The measurement itself was carried out only in the X axis up to a maximum distance of 350 cm, which corresponded to the radius of the illuminated area (Figure 11). As the illuminated area was a symmetrical cone, the measurement was carried out only in one direction: from the center to the \"right\" side. Therefore, the measured values for one direction corresponded to the measurements in every other direction (this statement was tested and verified by random short measurements). The Rohde & Schwarz ZVB4 network analyzer was used to measure the attenuation characteristics of the entire communication chain. This attenuation frequency response was measured against the reference that was set when the analyzer input and output were connected directly. After measuring this characteristic, it was decided that the measurement would be carried out at a carrier frequency of 3 MHz, mainly to use as much bandwidth as possible. The attenuation frequency characteristics measured at various distances (1 m, 2 m, and 3 m) from the center of the illuminated area are visible in Figure 12 as well. It is noticeable that the attenuation rapidly increased with the increasing distance from the center. The dependence of \(\mathrm{E_{b}/N_{0}}\) on the measured distance and configured adaptive algorithm can be seen in Figures 13 and 14. These figures correspond to measurements with 4-QAM modulation and the 1 MHz or 4 MHz bandwidth. It is noticeable that the QR-RLS adaptive algorithm provided the best results of \(\mathrm{E_{b}/N_{0}}\) across the board (in comparison to the non-equalized data). The parameter was improved by 9 dB at the center of the illuminated area and by 11 dB at a threshold value of almost \begin{table}
\begin{tabular}{c c} \hline \hline
**Philips Fortimo LED 44W/840** \\ \hline Luminous power & 3000 lm \\ Active power & 46 W \\ Voltage & 220–240 V \\ Effectivity & 68 lm/W \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Parameters of the transmitting LED light source. Figure 11: Visualization of reached M-QAM modulation formats based on measured parameters—3 MHz channel width and carrier frequency. 300 cm. The other algorithms improved the measured signal as well, but the difference was lower. LMS managed to improve the \(\mathrm{E_{b}}/\mathrm{N_{0}}\) by 2 dB at the center and 7 dB at the threshold. NLMS improved the values by 3 dB at the center and 8 dB at the threshold. As is visible, each algorithm noticeably improved the received signal. Figure 12: Attenuation frequency response of the entire communication chain using a Philips Fortimo LED 3000 44W/840 lamp at a distance of 202 cm between the source and the photodetector. Figure 13: Dependence of \(\mathrm{E_{b}}/\mathrm{N_{0}}\) on the distance and adaptive algorithm, bandwidth 1 MHz, 4-QAM.