# Next-Generation Dual Transceiver FSO Communication System for High-Speed Trains in Neon Smart City
## 5 Performance Analysis
### Ln Ber  
The BER for NRZ-OOK can be denoted as a function of the SNR as [38]:  
\[\mathrm{BER}_{\text{\text{\text{\text{\text{  
atmospheric turbulence parameters specific to Neom city according to the methodology outlined in [34]. Additionally, the system operates at an 850 nm wavelength, which ensures safety and is suitable for deployment in public areas. This wavelength falls within the near-infrared region known for its lower risk of adverse effects on human eyes. Moreover, we considered employing lasers classified as Class 1 or Class 1M, which are deemed safe for direct human exposure according to international laser safety standards. Class 1 lasers are considered safe under normal operating conditions and pose no hazards. They are considered incapable of producing damaging levels of laser radiation. Class 1M lasers, on the other hand, are safe for direct viewing as long as they are not observed through magnifying optics [42]. We assumed that the handover delay, indicating the time needed for each transceiver on the train to establish a connection with the BS, is 130 ms, as indicated in [21; 24]. Our proposed model was subjected to a comprehensive evaluation of system performance, considering both LN and GG channels from received SNR and BER perspectives. Additionally, a comparative analysis was performed, in which our results were compared with those of other existing FSO systems. We evaluated the BER performance of our proposed model using the commonly employed OOK modulation technique. Furthermore, in order to conduct a fair comparison with the models presented in [30], which involve an intermediate node between the transmitter and receiver, we evaluated the BER performance using the 4-PAM modulation technique for these models to maintain similar throughput. In the case of OOK, each time slot represents one bit since our model is a direct FSO system. On the other hand, we employed 4-PAM modulation technique for RIS- and relay-assisted FSO systems, which involves an intermediate node, where two bits are transmitted over two time slots. Therefore, both modulation techniques maintain a similar throughput of one bit per one time slot [43]. Figure 4a,b illustrate the received SNR versus the coverage distance along the track for a single transceiver FSO, RIS, and relay-assisted FSO communication systems in the presence of LN and GG channels, respectively. As shown, the single transceiver model demonstrates a superior coverage distance for both LN and GG channels, as it achieves a high received SNR at each BS compared to RIS- and relay-assisted FSO. One crucial reason for this improvement is that the intermediate RIS or relay node is positioned in close proximity to the transmitter, to provide an early signal boost in the transmission path, compensating for initial signal losses and atmospheric effects that may occur over longer distances. Additionally, aligning the node with the transmitter is relatively easier compared to aligning it with the receiver, simplifying the alignment process and reducing misalignment errors [30]. By expanding the coverage distance provided by each dual transceiver BS, the number of required BSs and handover frequency can be minimized for Neom's HSR line. Additionally, these findings emphasize the importance of channel