Performance of frame synchronization in automatic train control communications systems

The performance of the 40 bit frame synchronization sequence adopted for ATCS (automatic train-control systems) is examined in detail. A general expression is derived for the probability of synchronization as a function of the bit error and erasure probability, the overlap n, and the number of bit errors/erasures which are tolerated in the frame sync word. The probability P_D of successful frame sync with errors-and-erasures decoding is compared to P_D with errors-only decoding. For a given bound on false alarms, a significant improvement in P_D is found on random error channels if the receiver contains an erasure zone. An improved frame synchronization scheme which uses the preamble is shown to follow a higher error tolerance for a given false-alarm probability, and thus a higher P_D