Low-cost transponder system for data transmission to trains in remote areas

Intermittent transmission of geographical location information or command data to moving trains may be achieved by track-mounted transponders. A need for inexpensive, passive transponders that require no electronics in the track equipment exists in remote areas. A metal-plate transponder system, in which information is encoded in the plate pattern as laid between the running rails, is studied. The design problems are to devise reliable plate detector hardware and to select suitable decoding algorithms, and to achieve protection against erroneous bit detection and incomplete reading of the message bits. The design principles and performance characteristics are stated in detail. The system demonstrates the feasibility of bidirectional decoding with dual direction and orientation capability, low-speed detection, including stopping over the transponder, high-speed detection (with timing validation), and error control, including single-error correction