FRMCS Planning and Dimensioning: The Cornerstone of Cost-Efficient Deployment Strategies

The railway sector is navigating a pivotal transformation as it transitions from GSM-R (Global System for Mobile Communications – Railway) to FRMCS (Future Railway Mobile Communication System). This shift represents far more than a generational technology upgrade – it is a strategic overhaul of how mission-critical railway communications networks are conceived, dimensioned, and deployed to meet the demands of fully digital, high-performance rail operations.

GSM-R, rooted in 2G cellular technology, has reliably supported voice and limited data services for decades. In contrast, FRMCS builds upon a 5G architecture engineered to deliver broadband, low-latency, and ultra-reliable connectivity for next-generation rail operations. This evolution underpins capabilities that range from real-time predictive maintenance and high-definition video surveillance to autonomous train control operations, all of which impose significant demands on network performance, reliability and availability.

Dimensioning for FRMCS extends beyond just coverage and capacity calculations - it is a multi-factor, service-centric process that ensures the network consistently meets stringent targets for coverage, throughput, availability, and reliability. Unlike GSM-R’s relatively straightforward design model, the FRMCS network calls for an integrated radio planning approach that accounts for spectrum efficiency, using technology enhancements such as beamforming and MIMO gains, train speed impacts on (handover) performance, and resilience for safety-critical applications.

The cost implications are substantial. FRMCS deployment requires significant capital investment, and precise radio network dimensioning is essential to optimize asset usage, prevent bottlenecks or over-dimensioning, and guarantee seamless coexistence with GSM-R during the migration window. This includes sophisticated spectrum planning to balance new FRMCS bands with legacy allocations and potential shared use strategies involving Mobile Network Operators (MNOs).

In other words, for railway infrastructure managers, accurate FRMCS planning not only safeguards operational safety and service continuity, but also serves as the blueprint for cost-efficient deployment and migration strategies for future-proof transition. Railway specific competences and AI-driven tools are enablers for best re-use of GSM-R assets and best potential benefit of a shared infrastructure with Public Mobile Operators.

From GSM-R to FRMCS: A Paradigm Shift

Where GSM-R planning revolved around coverage and interference management, FRMCS planning is about ensuring end-to-end service quality under diverse operational conditions – from dense multi-track corridors and stations to high-speed lines where trains reach 300+ km/h.

In fact, GSM-R technology has been a reliable backbone for European railways, designed primarily for voice services with limited packet data transmission, with the following main characteristics:

• Operation in the 900 MHz band
• Planning driven by coverage and interference (parameters called Received Signal Level (RxLev) and Carrier-to-Interference (C/I) ratio)
• Capacity scaling by adding more frequencies (carrier)

To ensure optimal coverage and manage interference, GSM-R network planning focuses on carefully managing frequency optimization.

In contrast, FRMCS is 5G-based and designed for multiple packet data services (broadband voice, video, and mission-critical data) and introduces a host of advanced features and characteristics:

• Operation in the 900 MHz band and also 1900 MHz band
• Advanced features for coverage and reliability (such as beamforming, MIMO)
• Planning driven by throughput requirements with strong emphasis on interference mitigation (via site placement, antenna tilts, azimuths, and consideration of train speed dynamics).

Why is dimensioning key for FRMCS?

Dimensioning is the process of ensuring that the network can meet performance targets for capacity, availability and reliability while considering the constraints of limited spectrum. FRMCS dimensioning requires a careful balance of multiple interdependent factors:

• Trackside radio network design such as spectrum use, features use (e.g. beamforming), pylon characteristics (heights etc.), intercell distances
• Throughput requirements such as for critical signaling data transmission (ETCS), predictive maintenance traffic, real time video transmission
• Mobility such as train speeds ranging from low-speed shunting yards to 350 km/h high-speed lines
• Reliability and redundancy, as critical parameters for safety-related applications

Accurate expertise is needed to apply FRMCS-specific system simulations that model service level requirements, antenna parameters, power levels, impact (cell-edge) throughput and intercell distances. These simulations also integrate train speed performance curves and specific configurations (MIMO/beamforming) for both radio base stations and cab radios.

Advanced railway radio dimensioning tools calculate link budgets and capacity under realistic scenarios, enabling planners to avoid both over-dimensioning (unnecessary cost) and under-dimensioning (risk to safety and service).

Planning the Digital Railway

Planning a 5G FRMCS railway network requires a far more holistic approach than GSM-R:

• Capacity increases are achieved through network densification, not just channel additions
• Interference mitigation becomes multi-dimensional: site placement, antenna type, antenna tilts, azimuths, and train speed effects
• Railway-specific track planning is essential: scalable setups, cloud-based IT platforms for automation, and simulation environments tailored for both FRMCS and mobile network operator (MNO) cooperation
• A full digital chain in the planning process ensures accuracy and efficiency, integrating high-resolution railway specific geodata, calibrated propagation models, and AI-driven optimization
• Continuous updates of planning guidelines based on evolving industry developments and standardization ensure that FRMCS deployments remain future proof

Planning and Dimensioning as Input to Migration

One of the most strategic benefits of thorough FRMCS planning is its role in shaping the most accurate migration path from GSM-R and analog systems.

In fact, dimensioning enables key strategic approaches such as:

• Which GSM-R, Mobile Network Operator or analog infrastructure could be reused – sites, towers, backhaul links, and power supplies
• Where new densification is required, particularly around stations, yards, and high-traffic corridors
• Spectrum usage strategies – balancing own FRMCS spectrum with potential Public MNO (PMNO) slices, if applicable
• Service-level requirements for different track categories, from single rural lines to multi-track high-speed corridors
• Redundancy and reliability models, enabling safe coexistence during the transition phase

This knowledge translates into a solid FRMCS deployment and migration strategy that avoids unnecessary costs, reduces risk, and ensures operational continuity.

The migration from GSM-R to FRMCS is much more than a one-to-one radio layer upgrade – it is a shift in planning philosophy. GSM-R’s coverage-and frequency-based planning served well for voice and limited data needs, but FRMCS demands a multi-dimensional, throughput-driven, and service-quality-focused approach.

By starting with robust dimensioning, using railway-specific simulation tools, and embracing digital planning environments, infrastructure managers can avoid both over- and under-dimensioning, ensure compliance with stringent reliability demands, and position themselves to fully benefit from the potential of FRMCS.

Proper dimensioning and planning are essential to ensure FRMCS delivers on its promise, i.e. safe, reliable, and future-proof communications for railways. Just as importantly, these activities provide the foundation for migration strategies that leverage existing GSM-R and analog infrastructure, whilst also optimizing investments by securing the right amount of trackside radio sites.

In this sense, it represents both the cornerstone for efficient Total Cost of Ownership in FRMCS deployment strategy, as well as the enabler of a smooth transition to the digital rail operations and Gigabit trains.

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