From 18 to 22 codes: Modulation-based capacity expansion in railway track circuit

Abstract The ZPW-2000A track circuit’s limited low-frequency codes (18 types) constrain the train control system capacity. This study proposes code expansion via modulation coefficient optimization, adding four frequencies (8.1/9.2/30.1/31.2 Hz). Theoretical and simulation analyses confirm that the new codes maintain spectral consistency with existing standards, showing over 96% energy concentration for stable transmission. Hardware-software co-designed transceivers achieve secure detection of extended codes. Integrated with CTCS-3 systems, the technology reduces synchronization delay by 32%, shortens temporary speed restriction response time by 19%, and minimizes braking redundancy during communication failures. This advancement supports precision control in complex environments (e.g., Sichuan-Tibet Railway) and future ultra-high-speed systems.