# Next-Generation Dual Transceiver FSO Communication System for High-Speed Trains in Neon Smart City
## 5 Performance Analysis
### Ln Ber
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameter** & **Symbol** & **Value** \\ \hline Extinction Coefficient & \(\sigma\) & 0.44 dB/km \\ Wavelength & \(\lambda\) & 850 nm \\ Optical Transmission Power & \(\mathrm{P_{t}}\) & 40 mW \\ Additive Noise Standard Deviation & \(\sigma_{n}\) & \(10^{-7}\) A/Hz \\ PD Responsivity & R & 0.5 A/W \\ Detector Radius & a & 10 cm \\ Jitter Standard Deviation & \(\sigma_{\mathrm{g}}\) & 30 cm \\ Vertical Distance & \(\mathrm{L_{v}}\) & 3 m \\ Horizontal Distance & \(\mathrm{L_{H}}\) & 95 m \\ Train Length & \(\mathrm{L_{T}}\) & 200 m \\ TX/RX Tilting Angle & \(\gamma\) & 2.5 degree \\ HST Speed & V & 300 km/h \\ Refraction Structure’s Index & \(\mathrm{C_{n}^{2}}\) & \(1.26\times 10^{-14}\) m\({}^{-2/3}\), \\ (Weak-to-Strong Turbulence) & \(5.9\times 10^{-14}\) m\({}^{-2/3}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: System parameters. consideration, as the chosen channel significantly impacts the system's performance over longer distances, particularly in turbulent conditions. Therefore, a careful consideration of both LN and GG channels is essential for designing FSO systems in G2T applications, ensuring reliable communication across various turbulence scenarios. The BER performance of the dual transceiver model for NRZ-OOK with LN and GG distributed channel models for different propagation distances are presented in Figure 5a,b, respectively. The BER values are determined using Equations (16) and (18) for weak-to-moderate and strong turbulence, respectively. The results indicate that achieving a satisfactory BER under large propagation distances and strong turbulence requires high power. It is clearly depicted that the BER for the considered channels shows an improvement with increased SNR. Whether the turbulence strength is weak-to-moderate or strong, the consistency between the results obtained from numerical simulations and theoretical analysis is good. Monte Carlo computer simulations with \(10^{10}\) iterations were used to obtain the simulated BER. In Figure 6a,b, we present a comparison of the BER dual transceiver FSO, RIS-assisted FSO, and relay-assisted FSO under weak-to-moderate and strong atmospheric turbulence conditions, respectively [40; 44; 45]. It is evident that the dual transceiver model outperforms the relay-assisted FSO in both LN and GG channels. Furthermore, the RIS-assisted FSO exhibits a distinct performance variation between lower and higher SNR regimes. In high SNR conditions, the received signal strength is relatively strong compared to the noise level. This advantageous scenario allows the RIS to manipulate the signal more effectively. By optimizing the signal environment through adjusting the phase and amplitude of the reflected signals, the RIS enhances the signal power and quality [46]. Consequently, the RIS contributes to improving the received signal power, reducing fading effects, and enhancing the overall system performance. Additionally, it is worth noting that in high SNR regimes, the impact of channel impairments, such as atmospheric turbulence-induced  
Figure 4: Received SNR vs. coverage distance through: (**a**) LN channel; (**b**) GG channel. Figure 5: BER vs. received SNR of dual transceiver through: (**a**) LN channel; (**b**) GG channel for different propagation distances. fading and multipath propagation, is relatively reduced. This reduction can be attributed to the stronger received signal strength, which helps mitigate the adverse effects of these impairments. As a result, the RIS system's performance is enhanced in high SNR regimes. Table 2 provides a comprehensive overview of the required BSs for dual transceiver, RIS, and relay FSO communication systems, regarding Figures 4 and 6. Considering the HSR track of Neom city spans 170 km, we initiate the analysis by extracting the received SNR values from Figure 6 based on the specified BER detailed in the table for both channels. Subsequently, consulting Figure 4 allows us to ascertain the coverage distance values corresponding to the received SNR values.