# Flickering-Free Distance-Independent Modulation Scheme for OCC
## 6 Results
### Experimental Results  
In this subsection, the results for the three different proposed cases are presented, for all the cases 2500 2-bit symbols were transmitted:  
1. Short range: D = 15 m, \(\alpha=15\). 2. Medium range: D = 30 m, \(\alpha=30\). 3. Long range: D = 70 m, \(\alpha=75\). In this work, we have focused on the effects of the camera system (frame rate variations, lens distortion) and the PCC-based demodulation scheme on the detection process. In this way, we have excluded the noise level as a parameter in the experiments. Obviously, the noise level influences the system performance, particularly it introduces variations in the PCC obtained values. For this reason, decision regions for the symbols estimation have been established instead of specific values. Additionally, the use of several frames in the PCC value estimation has improved the obtained average value and reduced the noise effects. The main aim of the experimental setup is to analyze the characteristics of the proposed modulation without other external effects involved. However, this low noise setup is not ideal or theoretical at all, since the emitter and the receiver are already affected by thermal noise. Anyways, the noise influence over the system can be easily achieved in practice using an appropriate transmission power, camera gain, or optical zoom for example. Results from the first experimental case (\(\alpha=15\) and target distance D = 15 m) are depicted in Figure 14. The link presents a BER of \(5\cdot 10^{-4}\) when 3 consecutive frames are used in the PCC calculation algorithm. The same happened for a 20 m link, where the lamp's image in the camera was represented by 53 vertical pixels (1.5 bands). However, at 25 m where the lamp was represented by 43 vertical pixels (1.2 bands) the BER increases to \(2\cdot 10^{-2}\) for 3 consecutive frames, but stays at \(9\cdot 10^{-4}\) for 4 consecutive frames. Additionally, in all the cases, the succeed probabilities are above 99.8% and the BER values are below the FEC limit (\(3.8\cdot 10^{-3}\)) for distances up to 20 m.  
Figure 13: Example of obtained ROIs for \(\alpha=15\) at D\(=15\) m with the calculated PCC. Figure 15 shows the results corresponding to the \(\alpha=30\) and D\(=30\) m case. In this case, a BER of \(1.2\cdot 10^{-3}\) for the 3 consecutive frames based on PCC processing and \(1.1\cdot 10^{-3}\) for 4 consecutive frames were obtained. Then at 35 m and 40 m, where each frame captured 1.5 light bands, the link increased its BER to \(1.3\cdot 10^{-3}\) and \(1.8\cdot 10^{-3}\) correspondingly for the PCC estimation with 3 consecutive frames. However, in the case of 4 consecutive frames, the BER value did not change. While the BER was less than \(1\cdot 10^{-4}\) for 5 consecutive frames. Moreover, at 45 m where the lamp was represented by 24 vertical pixels (1.3 bands) the BER reaches \(4\cdot 10^{-2}\) for 3 consecutive frames, but \(2.9\cdot 10^{-3}\) for 4 consecutive frames, and \(1.5\cdot 10^{-3}\) for 5 consecutive frames. Additionally, in all the cases, the succeed probabilities are above 99.6% and the BER values are below the FEC limit for distances up to 40 m.  
Finally, as shown in Figure 16, for the \(\alpha=75\) and target distance D\(=70\) m case, an up to 90 m link was successful with BER of \(6\cdot 10^{-4}\) for 3 and 4 consecutive frames' PCC estimation. While at 95 m, where the lamp was represented by 11 vertical pixels (1.5 bands), the link has a BER of \(7\cdot 10^{-4}\) for 3 and 4 consecutive frames. Moreover, at 100 m, the distance where each frame captured 1.4 light bands, the BER increases to \(2\cdot 10^{-3}\) for 3 consecutive frames, and up to \(7\cdot 10^{-4}\) for 4 consecutive frames. Additionally, in all the cases, the succeed probabilities are above 99.6% and the BER values are below the FEC limit for distances under 100 m, and 99.8% for maximum 95 m.  
Figure 14: Communication BER for \(\alpha=15\). Figure 15: Communication BER for \(\alpha=30\).