# The Necessity of LED to Ambient Light Ratio Optimization for Vehicular Optical Camera Communication
## 4 Simulation
### Simulation Results
#### 4.4.2 Effect of LED Interval and Communication Distance  
(a) Effect of LED Interval  
This section provides simulation results to illustrate the effect of LED interval. The LED panel images were replicated with LED interval varying from 0.5 to 2. The communication distance and the L2A ratio are fixed at 50m and 1, respectively. The ambient light is set randomly in the range from 50 to 16,000 lux. The LED luminance is set based on the ambient light and the L2A ratio. The LED surface reflectance is set randomly in the range from 0.3 to 0.5. The ISO is set based on the ambient light. The remaining parameters are set to their fixed values given in Table 1.  
Figure 15 shows examples of LED panel frames replicated with LED intervals of 0.5, 1, 1.5, and 2, respectively. Note that the size of each individual LED is always fixed. Therefore, the size of the entire LED panel would increases as the LED interval increases. For the sake of clear illustration, the image of LED panels with smaller intervals, which have smaller sizes, are zoomed closer to keep the size of all LED panel images the same as shown in Figure 15. Because of the differences in the degree of zooming, images of LED panels in the left, which has smaller intervals, appear blurrier compared to that in the right in Figure 15. From this figure, it is obvious that the LED panels with smaller interval would have less LED distinguishability.  
Figure 16 shows examples of the distributions of LED features in ten frames replicated with different LED intervals but the same L2A ratio of 1 and the same communication distance of 50 m.  
Figure 17a shows the Bvar and Wvar at these LED intervals. The clusters of the On and Off LED features can be seen to become more compact as the interval increases. Therefore, the Wvar would decrease greatly as the interval increases. As the clusters of the On and Off LED features become more compact, the distance between the centers of the two clusters increases as the interval increases. However, an interesting phenomenon can be observed in Figure 16d: At the LED interval of 2, the clusters of the LED features appear to become more compact and the distance between the two clusters decreases. This is caused by two phenomena: The range of the GRI (which measures the interference between LEDs) decreases due to the decreasing interference. The range of the AGR (which measures the average greyscale  
Figure 16: Distribution of LED features at different LED intervals. (**a**) LED interval = 0.5. (**b**) LED interval = 1.5. (**d**) LED interval = 2.  
Figure 15: LED panel frames at different LED intervals.  
in each LED region) also decreases. Recall from Figure 2, the entire LED panel is divided into equal rectangular LED regions. As the LED interval increases, these rectangular regions become larger and decrease the average greyscale in each region. The decrease in the range of GRI and AGR leads to the decrease in the distance between the On and Off LED clusters, as well as the decrease in Bvar, as shown in Figure 17a. However, this would not negatively impact the separation of the On and Off LEDs as Figure 17b shows.  
Figure 17b shows the B2W variance ratio at different LED intervals. Because Bvar increases and Wvar decreases, the B2W variance ratio greatly decreases as the interval increases. At the LED interval of 2, Bvar decreases. However, the great decrease of Wvar causes the B2W variance ratio to eventually increase sharply.