Frame sync ambiguity in simple fibre-optic telemetry

A simple method of avoiding ambiguity of frame sync recognition in fiber-optic telemetry is described. The method involves an addition of only one bit at the beginning or end of each channel. In order for the method to be effective, two conditions must be satisfied: (1) the frame sync code should be all 1's or all 0's before the addition of the ambiguity bit, and (2) the frame sync should be an unacceptable word anywhere else in the frame except at the beginning of the frame, i.e., the frame sync code word should not be a data word in other channels.