# Free Space Optics Communication for Ultra-High-Speed Train Running in Evacuated Tube
## 4 Results and Discussion
### Simulation Results
#### 4.1.3 Data Rate  
The data rate is calculated by using Equations (13) and (14). In the theoretical values displayed in Figure 13, the transmitted power is 27 mW as indicated before, and the data rate for the nearest point to the BS with narrow divergence angle indicates to be more than 4 Tbps. In contrast, the wide divergence angle in the figure shows a high data rate of more than 500 Gbps. Moreover, the data rate results showed the advantage of using narrow angles instead of wide angles.  
\begin{table}
\begin{tabular}{c c c} \hline
**Full Divergence Angle** & **Distance(m)** & **Received Power in dBm** \\ \hline
6.944 \(\times\) 10\({}^{-5}\) & 1500 & 20 \\  & 14,200 & 10 \\  & 550 & 20 \\  & 1500 & 17.5 \\  & 14,200 & \(-\)2.1 \\ \hline \end{tabular}
\end{table}
Table 6: The received power for variable distance with two types of divergence angles (\(P_{tx}\) = 1 W).  
Figure 12: Received power versus distance for two values of the divergence angle (assuming a transmit power \(P_{tx}\) = 1 W).  
Figure 13: Data rate versus distance for two values of the divergence angle.  
Finally, Figures 14 and 15 are utilized to describe the actual contribution of the suggested method in terms of time connectivity and the number of BSs employed in the systems compared to other works in the literature.  
Figure 14 illustrates the time connectivity for the proposed method (i.e., the time the train remains successfully connected to a BS), including the two train speeds, 1000 km/h and 2700 km/h. Additionally, the figure compares the results to those of [1], who also used FSO in an ultra-high-speed train. The other methods in the literature designed FSO's BSs only for a high-speed train (the train speed up to 400 km/h, not ETT). The best results in these works have a time connectivity for each BS of 2.8 s and 1.06 s [5].  
The red bars in the figure indicate the train speed of 2700 km/h, and the blue bars represent the train speed of 1000 km/h. The figure also shows that the time connectivity for the other approach is 0.72 s for the train speed of 1000 km/h. While the proposed method has a time connectivity of more than 47 s, the time connectivity to the compared approach [1] is 0.26 s at a speed of 2700 km per hour. However, the proposed technique indicates 14.8 s for each BS, which affects favorably the frequency of the handover mechanism.  
Figure 15 shows the number of BSs required to provide coverage for each 100 km; additionally, the figure includes a comparison with the method of [1], which is used in  
Figure 14: The time connectivity for the proposed method with others.  
Figure 15: The number of base stations required for 100 km.  
an ultra-high-speed train, because the other methods (as with the time connectivity case) designed FSO's BSs only for a high-speed train (the train speed up to 400 km/h), where the best results show that 125 BSs are used for 100 km [5].  
The figure also demonstrates that the other strategy [1] requires 500 BSs at any speed. At the same time, the proposed technique has less than 9 BSs at a train speed of 2700 km/h, and fewer than 8 BSs for a train speed of 1000 km/h.  
These results are optimistic regarding time connectivity or reducing the number of BSs necessary for design, while maintaining the maximum data rate.