# Next-Generation Dual Transceiver FSO Communication System for High-Speed Trains in Neon Smart City
## 2 Related Works  
Effective telecommunication plays a vital role in the performance of railway transportation within smart cities, given the extensive scale, large distances, numerous employees and passengers, and their continuous mobility. The importance of communication technologies in the railway system is evident in multiple aspects, including the provision of accurate and real-time train location information and facilitating the simultaneous operation of multiple trains on the same track. This importance underscores the essential role of efficient telecommunication in optimizing the efficiency and effectiveness of railway transport systems within smart cities [6]. Despite the progress made in communication technologies, ensuring optimal quality of service (QoS) for forthcoming HSTs remains a formidable task. The main challenges arise from the dynamic nature of wireless channels, which are characterized by frequent fluctuations over time and non-stationarity. In addition to the aforementioned factors, other challenges that affect QoS include co-channel interference, significant path loss attenuation in millimeter-wave and terahertz frequency bands, frequent handovers due to limited coverage area for each BS, and notable doppler shifts. Consequently, it becomes crucial to address these issues effectively to ensure dependable and efficient communication for HSTs [7; 8]. Optical wireless communication emerges as a promising wireless access technology that offers potential solutions to the challenges faced by proposed radio frequency (RF) wireless systems in HSTs. Its aim is to satisfy the expanding need for high-quality multimedia services in HSR systems. These advantages include access to a vast unregulated spectrum, immunity to electromagnetic interference, enhanced security due to the inability of optical beams to penetrate opaque objects, and the ability to achieve high capacity per unit volume through frequency reuse. FSO systems are well-suited for environments where the utilization of RF-based systems is constrained or prohibited, including hospitals, airplanes, and military locations, where RF signals may cause interference with monitoring equipment. The versatility of FSO technology allows for its deployment in both indoor and outdoor settings, facilitating the transmission of extremely high data rates reaching up to gigabits per second [9; 10; 11; 12; 13; 14; 15; 16; 17]. [PERSON] et al. [18] presented a ground-to-train (G2T) FSO communication system designed for high data rates. The system demonstrates rapid acquisition time and high-speed handover, achieving approximately 100 ms. It also attains impressive data rates of around 1 Gb/s. The authors of [18] discuss the utilization of acquisition-tracking-pointing (ATP) mechanism and handover techniques to ensure continuous connectivity. The concept of G2T in FSO communication utilizing a Gaussian laser beam was explored by the authors in [19]. They introduced a mathematical model to address the communication link, considering the challenges associated with train aerodynamics. The presented system offers a promising solution for facilitating high-bandwidth communication between the BSs and trains, thereby enabling internet services for train passengers. In [20], a G2T FSO system is implemented by placing light-emitting diodes (LEDs) at BSs positioned along the tracks to illuminate the approaching trains with optical signals. LEDs are selected as the optical source because of their safe and wide emission properties. The authors of [21] proposed a scheme where a rotating transceiver is used for FSO communication in G2T environments. The objective of this scheme was to overcome the difficulties associated with frequent handovers and alignment problems in HST environments. Accordingly, a mechanical gimbal system is employed to rotate the transceivers located on both the train and BSs. This innovative approach ensures uninterrupted line-of-sight (LOS) communication.