Multi-RIS-assisted Railway Communications in Tunnel using CloudRT simulator
Authors:
Aline Habib, Ammar El Falou, Charlotte Langlais, Marion Berbineau
Abstract:
High data rates are increasingly required in railway communications to support services such as video
streaming, passenger connectivity, real-time monitoring, and safety-critical applications. Although
millimeter-wave (mmWave) frequencies meet these demands due to their large available bandwidth, their strong
sensitivity to blockage significantly limits their coverage, particularly in confined environments such as
tunnels, where tunnel walls, ceilings, and train carriages can obstruct signals. In this context,
Reconfigurable Intelligent Surfaces (RIS) have emerged as a promising solution to overcome signal-blocking
issues by enabling additional propagation paths. However, due to the high signal attenuation in tunnel
environments, a single RIS is generally insufficient to ensure reliable communication throughout the tunnel.
Consequently, multiple RISs must be deployed along the tunnel to maintain an acceptable received signal. This
paper investigates the effectiveness of multi-RIS-assisted systems in tunnel scenarios. An optimization
algorithm is proposed to determine the optimal number and placement of RISs within the tunnel. A ray-tracing
simulator, CloudRT, is used to generate realistic channel coefficients. As RIS functionality is not
integrated into the simulator, we extend it by modeling the RIS as a virtual receiver-transmitter phased
array antenna. The simulation results show that in tunnel scenarios where the direct Tx–Rx link is blocked
by a train, placing the RIS on the tunnel’s ceiling yields better performance than mounting it on the
tunnel’s walls. Moreover, the Rx can achieve a good signal-to-noise ratio (SNR) using a reasonable number of
RISs of practical size.
