Railways are grappling with the challenge of migrating from their current GSM-R systems to the 5G based Future Radio Mobile Communication System (FRMCS) standard. The plan from the International Union of Railways (UIC), the European Agency for Railways (ERA) and Europe’s Rail Joint Undertaking (ERJU), who are jointly responsible for the FRMCS programme, calls for first deployment in 2027.

FRMCS will digitalise railway operations, respond to GSM-R obsolescence and support further automatic train operations (ATO) by embracing the possibilities offered by 5G. Implementation aims to be cost effective and future-proof, interoperable, and allow seamless migration of GSM-R to FRMCS. Today GSM-R forms the underlying connectivity layer for safety critical applications specified by the Technical Specification of Interworking (TSI). An official change to the TSI allowing FRMCS requires a validation process, which is the key goal of the 2026 FRMCS trial programme.

Deploying FRMCS will be challenging, especially considering that it needs to happen while GSM-R is still operational. To face this challenge, railways need innovative approaches to enable cost-effective and future-proof ways to start deploying FRMCS in parallel to GSM-R. Leveraging the rich 5G NR feature set and the new 1900 MHz railway spectrum band, as well as collaborating with Mobile Network Operators (MNOs) on possible synergies, are key concepts.

Ericsson recommends that initial deployments of FRMCS should focus on providing coverage with the 1900 MHz as an overlay. For redundancy, existing GSM-R coverage should be utilised where available. Ericsson offers a multi-band antenna supporting FRMCS 1900 MHz and GSM-R 900 MHz.

Infrastructure Managers want to maintain the average intersite-distance (ISD) used in current GSM-R deployments to limit additional densification and costly additional track-side infrastructure. To address this, the graphic below shows an example average ISD for different GSM-R and FRMCS base station configuration choices, in different environments and with moderate loading. Average ISD has been computed assuming a required uplink (UL) cell-edge bitrate of 3 Mbps. This target is based on having two trains passing at the cell edge using 1 Mbps each, with some capacity available for trains closer to the cell site.

The example in rural scenarios shows that using 1900 MHz FRMCS, with 8x8 MIMO configuration, allows an average ISD within the range of current GSM-R ISD. Consequently, railways could deploy FRMCS in 1900 MHz with confidence by limiting densification on top of existing rural GSM-R sites. By using FRMCS in 1900 MHz they reduce the risk of possible interference with GSM-R 900 MHz while GSM-R remains in operation.

While railway infrastructure managers can primarily use the 1900 MHz rail spectrum to start, they could also collaborate with MNOs on hybrid network deployment models. Advantages include integration of public networks to offer redundancy and additional capacity, as well as shared investment in infrastructure.

While redundancy can be built using additional deployment of dedicated network components, as done in GSM-R, the partial use of MNOs’ existing 5G infrastructure can create savings and enhance the available network capacity to trains. When additional infrastructure is needed, synergies between railways and mobile operators are possible, from sharing of passive infrastructure (such as towers, fibers, and power) to parts of active networks components.

There are two main models being tested in coming FRMCS trials using 5G spectrum sharing to integrate a public network into the dedicated railway network.

The first is a Multi Operator Core Network (MOCN), where a radio site along the track is shared and connected to both core networks - the railway’s dedicated core and the MNO public core. This is a resilient and secure configuration allowing railways to operate end to end services independently of the MNO core network. In MOCN, the on-board radio can smoothly hand over between dedicated and shared spectrum.

The second model is National Roaming. It allows a train to move between networks that provide radio coverage in the current location of the train, while staying connected throughout the journey. The overall MNO network - core and radio access parts - is used for railway operations in areas not covered by the railway’s dedicated network.

Irrespective of the model used, it is possible to utilise both the railway dedicated network and the MNO network simultaneously with more than one User Equipment (UE) on the train, each using its own SIM card and subscriber profile. FRMCS can utilise these multiple connections simultaneously, further enhancing the train’s connectivity, such as the ability to dynamically switch an application’s connectivity from one onboard radio module to another in case the connection via one UE fails or experiences degraded quality.

In defining their FRMCS strategy, railways should ensure they consider different approaches, like the examples above, to make deployment smooth and cost effective.

For more information, please visit ericsson.com/rail

Ericsson is attending the UIC Global FRMCS conference 2024 on November 19-20 in Paris.