Distributed Hierarchical Slack-Reduction in Slicing for Railways FRMCS

The Future Railway Mobile Communication System (FRMCS), based on 5G technology, is being developed to support high-speed train mobility and increasing data-rate demands within the limited 5-10MHz frequency bandwidth allocated to railway operators. The fluctuating channel conditions and limited radio resources present a significant challenge for the Radio Access Network (RAN). Railway communications are structured around application-specific requirements, categorized into three classes: critical (ultra-reliable train control and safety operations), performance (bandwidth-intensive services like video surveillance and infotainment), and business (on-board Wi-Fi). Existing RAN slicing solutions, are designed for public 5G Networks, assume wideband carriers or static quotas at slice level or user level, so they cannot guarantee application-level requirements or adapt to dynamic channel-quality indicator (CQI) swings in railways. That is why we propose HSRS (Distributed Hierarchical Slack-Reduction Slicing), which formulates this NPhard allocation problem as an integer linear program and applies a two-phase heuristic: 1) minimize SLA slack for critical; 2) maximize weighted throughput for performance and business slices. Simulations using SNR traces captured on real trains traveling up to 350kmh demonstrate the improved application-level SLA satisfaction compared to baseline methods.