## 3 Experiment and Result
### Result and Analysis
Sometimes LEDs will be shielded or broken, where most existing VLP methods would fail. In contrast, our algorithm realizes high-accuracy positioning under shielded effect by introducing unscented Kalman filter into the mean shift algorithm. The MS has wonderful robustness when the backgrounds are not complicated as shown in \[D=\sqrt{\left(X-X_{r}\right)^{2}+\left(Y-Y_{r}\right)^{2}} \tag{44}\]1 However, the algorithm proposed in Reference [9] would lose the LED under the same circumstance. When the LED is shielded, the tracking results of the MS is treated as the observation model of the UKF, combined with the noise matrix to get the final output. Through these measures, the shielded LED can be located with relatively high accuracy and little computational burden. The performance of our proposed algorithm when half the area of the LED is shielded is shown directly in \[D=\sqrt{\left(X-X_{r}\right)^{2}+\left(Y-Y_{r}\right)^{2}} \tag{44}\]2  
\[D=\sqrt{\left(X-X_{r}\right)^{2}+\left(Y-Y_{r}\right)^{2}} \tag{44}\]3 The calculation process of maximum motion speed of the positioning terminal. In addition, a script was written to make the turlebot3 robot move with the fixed route. Several videos were recorded where the LED was shielded at different degrees and the shielded area varies from 30 percent to 90 percent of the original area. Seventy-four frames where random areas of the LED are shielded and 59 frames where nearly 50 percent of LED's area was shielded were chosen to analyze the performance of our proposed algorithm handling the circumstances of the shielding effect, whose performances are shown in Figures 19 and 20. \[D=\sqrt{\left(X-X_{r}\right)^{2}+\left(Y-Y_{r}\right)^{2}} \tag{44}\]4 The error under the circumstance where nearly 50 percent of the LED’s area was shielded. \[D=\sqrt{\left(X-X_{r}\right)^{2}+\left(Y-Y_{r}\right)^{2}} \tag{44}\]5 The tracking performance when most of the LED is shielded. \[D=\sqrt{\left(X-X_{r}\right)^{2}+\left(Y-Y_{r}\right)^{2}} \tag{44}\]6 The tracking performance when half of the LED is shielded. The average tracking error was 1.41 cm when nearly 50 percent of the LED was shielded. When the LED was shielded randomly, the average positioning error was 1.52 cm. Besides, the average error of the x coordinates in Figure 19 was 0.67 cm and that of the y coordinates was 1.00 cm. In Figure 20, the error of the x coordinates and y coordinates were 0.84 cm and 0.87 cm, respectively. The CDF plot of data measuring the position error in Figures 19 and 20 are shown in Figures 21 and 22, respectively. From Figure 21 we can learn that more than 90 percent of tracking error D, the error of x coordinates and y coordinates were less than 2.11 cm, 1.88 cm, and 1.44 cm, respectively when nearly half of the area of the LED was shielded. Meanwhile, these data indexes were 2.11 cm, 1.83 cm, and 1.91 cm, respectively, when random areas of the LED was shielded. These results demonstrate the excellent robustness of our proposed algorithm. Though the positioning accuracy and the real-time ability of our proposed method did not achieve the most advanced level at present, they are excellent enough compared with most of the VLP systems. Moreover, the strong robustness of our system is unique in the field of VLPs. Before our previous work [9], nobody discussed the aspect of robustness in the field of VLP. Furthermore, the focus of this article is not to improve the real-time ability, robustness or accuracy of the system alone. It is not difficult to improve the performance of any single aspect, but the improvement of them all at the same  
\[D=\sqrt{\left(X-X_{r}\right)^{2}+\left(Y-Y_{r}\right)^{2}} \tag{44}\]7 The CDF of positioning error when nearly 50% of the area of the LED was shielded. \[D=\sqrt{\left(X-X_{r}\right)^{2}+\left(Y-Y_{r}\right)^{2}} \tag{44}\]8 The error under the situation where random areas of the LED was shielded. time and maintaining balance is hard. The key point of our work is balancing the accuracy, robustness, and real-time ability of a VLP system.