# Flickering-Free Distance-Independent Modulation Scheme for OCC
## 5 Methodology
### Experimental Setup  
As stated previously, a field test is required for validating the proposed modulation scheme under realistic conditions. All the experiments were held during sunlight days with similar environmental conditions: temperature below 30 \({}^{\circ}\)C, low wind-speed, without the presence of haze or rain. However, as explained in the system advantages, the background illumination effect is eliminated due to the normalization and the calculation of the average PCC. For this experiment, the emitter was a \(60\times 60\) cm\({}^{2}\) commercial LED-based square panel with effective vertical distance of \(d_{y}=0.595\). During transmission, this lamp was activated by a squared signal with duty cycle of 50%. However, when the panel was on waiting state, the device transmits a continuous signal. Since, the signal normalization processes allow the receiver to work properly from a minimum emitted power level, the experimental setup established this transmission level in the lamp (a 10 V amplitude driving signal in this work was experimentally determined). On the receiver side, a Raspi Camera Module V2 was selected. This camera was mounted on a Raspberry Pi B for managing its characteristics and controlling the video acquisition. During the experiments, the resolution was set to 1920 \(\times\) 1080, while the frame rate was left as default (25 fps). For this combination, the vertical FOV is partial with a value of 34.65\({}^{\circ}\) (0.6048 radians) instead of 48.8\({}^{\circ}\), resulting in a camera's FOV and resolution ratio of \(\phi_{y}=5.5996\cdot 10^{-4}\). Additionally, the camera has high contrast, low brightness, focus to infinity, and automatic white balance. The camera was activated for recording videos of three minutes duration before the emitter started the data transmission. For each video, the resulting 4500 frames were stored in the Raspberry Pi memory card for off-line processing. For these experiments, three values of consecutive frames for representing each symbol were used (\(m=3\), \(m=4\), and \(m=5\)). Therefore, the 4500 frames transmitted 3000 (1500 symbols), 2250 (1125 symbols), and 1800 bits (900 symbols) in each case. Since the proposed modulation scheme requires at least two projected bands, for all the calculations \(v\) was assumed to be 2 for the worst case scenario. Additionally, the frequency multiplier was determined by applying Equation (9), resulting in a maximum value of 108 for the applied resolution \(N_{y}=1080\). However, the minimum frequency multiplier depends on the projected source size and therefore on the distance \(D\) between the emitter and the receiver. Then, this experiment was divided into three trial sets:  
1. Short range: D\(<\) 20 m.
2. Medium range: 20 \(<\)D\(<\) 60 m.
3. Long range: D\(>\) 60 m.  
In all the trials, the distance between the emitter and the receiver changes. This separation started at 5 m and the receiver was moved lineally 5 m at the time. Additionally, each symbol was repeated for three, four and five consecutive frames. For the short range case, the target distance was \(D=15\) m. For this separation, the selected light source (\(d_{y}=0.595\)) is represented by approximately 72 vertical pixels (calculated using Equation (6)). Therefore, the minimum frequency multiplier is calculated as follows:  
\[\alpha>\frac{v\text{FoV}_{y}}{4\bigg{[}\arctan\bigg{(}\frac{d_{y}}{2D}\bigg{)} \bigg{]}}\]  
\[\alpha>\frac{2*0.6048}{4\bigg{[}\arctan\bigg{(}\frac{0.595}{2*15}\bigg{)} \bigg{]}}\]  
\[\alpha>14.99\]This value was selected for the experimental implementation. The system's frequencies were determined with Equation (13), while by applying Equation (7) a strip's size of 36 pixels was calculated. The calculated frequencies are shown in Equation (14). For experimental reasons, the frequencies were set to their approximations. \[f_{\text{SW}}=