Algorithm for Rapid Acquisition of a PPM Optical Signal

An algorithm for rapid acquisition of a pulse-position-modulation (PPM) optical data signal implements a pattern-matching technique for synchronization of receiver timing with the temporal boundaries of data frames. Synchronization is necessary because in PPM, information is conveyed by the time slot during which a pulse is detected. Fast acquisition of a signal depends on detection of pulses in noise, and on correct estimation of the times of detected pulses. To facilitate synchronization at the receiver, a transmitter periodically inserts a prescribed sequence of pulses — the synchronization sequence or word — into the transmitted data stream. Older PPM-signal-acquisition algorithms are based on correlations and depend on reception of the full synchronization word (128 bytes long in some applications). The present algorithm is more computationally efficient and is capable of achieving synchronization with part of the synchronization word — typically with as few as 2 to 6 bytes.