Relayed FSO Links for Ground-to-Train Communications

Relay assisted FSO, which is primarily used as a fading mitigation technique, can be employed to reduce the impact of network layer handover in the context of HST communications. In this paper, we propose a relay-based FSO system to provide ground to train communications and relays the information to the next base stations. Two schemes are analyzed via numerical simulations namely (i) all optical amplify and forward (AOAF); and (ii) AOAF with optical and optical-electronical-optical regeneration schemes in terms of the bit error rate performance and transmission range attained

Sectorised base stations for FSO ground-to-train communications

Evolution and accessibility of smart-phones have led to a huge demand in network bandwidth. The ubiquitous use of smart-phones in high-speed trains poses a unique challenge in delivering high-speed internet service on board. This challenge can be overcome by employing free-space optics, an alternative to radio-frequency technology. Previous coverage models for ground-train communications employed single laser systems with a larger divergence angle to cover a larger distance. Larger divergence angles lead to larger geometric losses, which may result in a non-reliable communication link. This study proposes a sectorised multi-beam coverage model with a smaller divergence angle to reduce the impact of geometric losses in the system. This study also proposes two receiver (Rx) architectures for Rxs deployed on the train. Along with geometric losses, the atmospheric attenuation is taken into consideration for the FSO link. The performance of the ground-train communications system in terms of bit-error-rate is evaluated under weak turbulence conditions via numerical simulation

Reconfigurable Intelligent Surface Assisted High-Speed Train Communications: Coverage Performance Analysis and Placement Optimization

Reconfigurable intelligent surface (RIS) emerges as an efficient and promising technology for the next wireless generation networks and has attracted a lot of attention owing to the capability of extending wireless coverage by reflecting signals toward targeted receivers. In this paper, we consider a RIS-assisted high-speed train (HST) communication system to enhance wireless coverage and improve coverage probability. First, coverage performance of the downlink single-input-single-output system is investigated, and the closed-form expression of coverage probability is derived. Moreover, travel distance maximization problem is formulated to facilitate RIS discrete phase design and RIS placement optimization, which is subject to coverage probability constraint. Simulation results validate that better coverage performance and higher travel distance can be achieved with deployment of RIS. The impacts of some key system parameters including transmission power, signal-to-noise ratio threshold, number of RIS elements, number of RIS quantization bits, horizontal distance between base station and RIS, and speed of HST on system performance are investigated. In addition, it is found that RIS can well improve coverage probability with limited power consumption for HST communications.Comment: 14 figures, accepted by IEEE Transactions on Vehicular Technolog