EFFECT OF IMPERFECT SLOT SYNCHRONIZATION ON DIRECT-DETECTION OPTICAL SYNCHRONOUS CDMA COMMUNICATION-SYSTEMS WITH PPM SIGNALING

Effect of imperfect slot synchronization between the transmitter and t he receiver on optical synchronous code-division multiple-access (CDMA ) systems using pulse position modulation as data modulation (PPM/CDMA ) is investigated. Optical orthogonal codes (OOC's) are employed as si gnature sequences, and parallel optic-fiber delay line encoders and co rrelators are adopted in the transmitters and the receivers, respectiv ely. The upper bound on the bit error probability of PPM/CDMA is deriv ed under the condition that the receiver slot timing shifts from the t ransmitter timing clock. The bit error probability performance is eval uated for some values of the number of slots per frame, average signal photocount, and the number of simultaneous users. It is shown that as the number of slots per frame increases, the timing offset should be restricted to be smaller to achieve low bit error probability. Further , when the timing offset is small, the improvement of the bit error pr obability performance with the increase of the number of slots per fra me under the photocount per second constraint is shown to be larger th an that under the photocount per symbol constraint.