This paper describes the prototype and tests carried out to demonstrate the feasibility of implementing 4G/5G systems based on mobile network operators (MNOs) to transmit signalling critical data for railway systems as part of a possible solution for the Future Railway Mobile Communication System (FRMCS). This communication system design is performed from a protocol-stack perspective, introducing the KPIs for the physical layer (RSRP, RSRQ and SINR), network layer (latency and jitter) and application layer (signalling communication timeout). The analysis focuses on the characterisation of signalling critical railway data to assess the data traffic behaviour in a telecommunications laboratory. Finally, the study validates the approach in a realistic railway environment.

The next generation of mobile communications, 5G, will provide a wideband network based on microwave and millimeter‐wave (mmW) communication radio links with the goal of fulfilling the strict and severe requirements of the future test cases. In particular, this paper research is focused on mmW bands in metropolitan railway tunnels. For that purpose, a propagation measurement campaign was performed at 24 GHz band in a passenger train on a realist subway environment, and these results were combined with simulations ad hoc for tunnels and a theoretical modal propagation model. A narrowband and a wideband study have been conducted with the aim of obtaining the path loss, fading, power‐delay profile, and angle of arrival, taking into consideration horizontal and vertical polarization in the receiving and transmitting antennas. This validation can be used to design and deploy wideband mobile communication networks at mmW bands in railway scenarios.

An Outdoor-to-Indoor (O2I) wireless link allows obtaining information from devices located outside a train. This is the case for devices installed on the roof that need to be monitored wirelessly by data-collecting devices located inside the train. In these situations, the electromagnetic signal is diffracted around the structure of the train and reflects on the environment or goes into the car through the windows. This creates a non-line-of-sight channel which is strongly dependent on the physical structure of the train, its materials, and the surrounding environment. In this work, the O2I channel of a metro car is characterized at 2.6 GHz. Narrowband channel measurements are carried out in station, tunnel and open field environments, and obtained results are modeled and discussed.