OPTIO operating on hybrid private 5G

• The solution transfers intelligence to the train and allows the automation of railway operations.
• The project has been funded by the European Union and supported by the Government of Spain.

CAF has completed a key phase of its signalling innovation strategy with the validation of OPTIO, its CBTC (CommunicationsBased Train Control) system, operating on a private 5G network with the capacity to hybridise with the public network. The project, developed within the framework of REMIRO5G MULTINET, consolidates a unique communications architecture capable of supporting critical signalling services and non-critical operation services in metropolitan environments.

Since its definition, the project has pursued three operational objectives: to integrate in a single 5G infrastructure communications that traditionally require multiple networks (proprietary WiFi for CBTC, WiFi for CCTV/diagnostics and TETRA/GSMR for mission-critical voice), to ensure low response times and high availability for critical applications by switching between private and public networks,  and characterize radio propagation in tunnels to optimize deployments. With this scope, CAF has undertaken a complete engineering cycle that includes the identification of CBTC requirements on 5G, the design of the private network in standalone architecture, its verification in the laboratory and subsequent validation in a real environment, in collaboration with Cellnex/Tradia.

The technical execution has been articulated in consecutive stages. First, a validation of the solution was carried out in the laboratory and its deployment in a mock-up to validate end-to-end connectivity, security and routing by service-specific DNNs (CBTC signaling and MCX traffic). The solution was then moved to the real demonstrator operating in the n40 band (2300 MHz) with private 5G infrastructure. In the field, static and dynamic tests were carried out by performing coverage and latency measurements and verifying the continuity of the connection in the handovers between cells and BBUs, as well as hybridization tests of public/private networks with balancing of non-critical traffic. During the initial auscultations, latency discontinuities associated with BBU changes were detected that were mitigated with engineering adjustments; Under the corrected configuration, end-to-end latencies were typically maintained between ~10 ms and 40 ms across most circulations. The technical team also documented sensitive sections in which specific improvement measures were applied, along with specific corrections to cabling, power and configuration of on-board routers.

The results confirm the technical feasibility of OPTIO operating on a private 5G network with public support, with metrics compatible with the requirements of the CBTC and with a modular and open architecture that facilitates the evolution of the system. The consolidation of critical and non-critical communications into a single infrastructure reduces CAPEX and OPEX and reduces the footprint of on-track equipment, contributing to more resilient and sustainable networks.

CAF continues the optimization plan in sections with greater radio demand and the validation of nominal and degraded modes, in parallel with the preparation of integration scenarios with operators for future implementations. The collaboration with Cellnex has been decisive in the deployment and management of the private 5G network, and hybridisation with public networks is a differential element to guarantee service continuity in the event of incidents on the main network.

This innovation project has been financed by the European Union through NextGenerationEU funds and supported by the Government of Spain through the UNICO SECTORIAL 2023 program of the Ministry for Digital Transformation and Public Function.