Safety and reliability of synchronizable digital coding in railway track-circuits

The incorporation of digital error-control coding into railway track circuits represents a new approach for track-train data transmission for automatic train control. Methods based on error probability analysis are presented for assessing the safety and reliability of synchronizable error control coding in this application. The results for a sample coding scheme have been verified by experimentation using a calibrated source injecting audio-frequency Gaussian noise into a practical track circuit. Safety and reliability must be traded off, although the safety can be increased by incorporating dictionary checking in the code-receiver algorithm and the reliability can be enhanced by allowing single synchronization error correction. The technique demonstrates the possibility of designing a track-circuit data transmission system to given target safety and reliability levels of the same order of magnitude as the known failure rates of existing equipment