Optimal construction of synchronizable coding for railway track circuit data transmission

A new application using synchronizable error-control coding for train detection and track-train data transmission with audio frequency railway track circuits is described, with algorithms for quasi-optimal code construction and performance assessment. A new coding format is presented for frequency-shift-keying-modulated track circuits with which a fixed-duration-message telegram is transmitted. Only two-track-circuit separation frequencies are required, and although there exists a maximum rate of transmission for a given track-circuit parameter set, the data transmission capability is in general limited only by the telegram length. The problem addressed is that of assigning codes within the message to satisfy target safety and reliability criteria. The proposed telegram-type code comprises a synchronization sequence followed by message data bits arranged as three blocks and terminated by error-control bits with a final parity check. Data encoding is by conventional Hamming codes. Several hundred messages are available for typical track-circuit parameter sets