In the future railway services, wireless communication is the fundamental part and millimeter wave (mmWave) is foreseen to be a key enabler towards the smart railway. An accurate understanding of the propagation environment can assist designing both systems and railway infrastructures for better communication services. In this paper, the influence of typical objects to the mmWave propagation channel are analyzed for "Train-to-infrastructure" and "Intra-wagon" railway scenarios with various configurations. Propagation measurements are conducted in the mmWave band for the 12 most common railway materials. The corresponding electromagnetic parameters are obtained and a 3D ray tracing (RT) simulator is calibrated. The mean absolute error of the simulated S21 parameter is-53.5 dB, indicating that the calibrated RT can be used to generate the close-to-real mmWave channel for railway scenarios. Statistically consistent scenarios and deployments are generated, which enables drawing unbiased numerical results based on intensive RT simulations. The influence of typical objects and corresponding material compositions are then compared and significant objects are determined for each scenario. The results of this work not only imply how the propagation environment impacts on the propagation channel, but also makes suggestions to efficiently reconstruct railway environment models for an accurate RT based channel model. Moreover, the understanding of the influence of the environment at object and material levels will in turn guide the construction of railway infrastructure for better railway services.

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This paper explains the main results obtained from the research carried out in the work package 2 (WP2) of the Roll2Rail (R2R) project. This project aims to develop key technologies and to remove already identified blocking points for radical innovation in the field of railway vehicles, to increase their operational reliability and to reduce life-cycle costs. This project started in May 2015 and has been funded by the Horizon 2020 program of the European Commission. The goal for WP2 is to research on both technologies and architectures to develop a new wireless Train Communication Network (TCN) within IEC61375 standard series. This TCN is today entirely wired and is used for Train Control and Monitoring System (TCMS) functions (some of them safetyrelated), operator-oriented services and customer-oriented services. This paradigm shift from wired to wireless means a removal of wirings implies, among other benefits, a significant reduction of life cycle costs due to the removal of cables, and the simplification of the train coupling procedure, among others. IntroductionRailways are evolving very rapidly to meet the increasing demands of its users. Rolling stock is a cornerstone in this development, but there are some blocking points that need to be addressed. This is the main purpose of the EU-funded Roll2Rail (R2R) Project. Work package 2 (WP2) is focused on communication issues (which is one of the most challenging fields in railways [1]), and its final objective is to specify the requirements (and validate in a laboratory) for a wireless train communication network (TCN), at least with the same performance as the wired one. This wireless TCN would be very helpful to design, manufacture, operate and maintain trains from LCC (Life-Cycle Costs) point of view and able to avoid a significant number of failures due to broken connectors and cables. The partners in this WP were fourteen of the most relevant railway companies (see Table I), working as a single one.The first task to meet this goal is to clarify the state-of-theart of both radio technologies and related initiatives [2]. This review considered radio technologies and services, not only in railways, but also in the aeronautic, industry and automotive fields. Some of them have proven to be very useful in certain aspects (like GSM-R for train-to-ground communications), but they are unlikely to meet the requirements in other aspects. 3GPP LTE [3] and the IEEE 802.11 standards (commonly known as WiFi) [4] completed with deterministic communication features are two of the technologies that were identified as potential choices for the R2R project. Cognitive radio [5] is also a suitable approach that can help to achieve some of the objectives.The structure of the paper is the following one: in section II the general requirements that a Wireless TCMS needs to meet are depicted; in section III it is provided a model for each one of the radio channels of the project; in section IV, the security and reliability, availability, maintainability, and safety (RAMS) issues are...

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.