Novel frame synchronization rule for optical DPPM systems with restriction of frame length

A novel frame synchronization rule is proposed for direct detection optical differential pulse position modulation (DPPM) systems under the assumption of slot synchronization. Under the new rule, the receiver counts the number of photons in the received signal not only at the pulse positions in the synchronization sequence but at the other slots which is not counted under the conventional rule. Thus the new rule can cope with the variable symbol length of DPPM systems. Under this rule with taking the restriction of the maximum and the minimum frame length into account, the frame synchronization probability of DPPM systems exhibits better performance than that of unrestricted DPPM systems under the conventional rule which cannot cope with the variable symbol length. Further, since the number of required slots in DPPM systems is smaller than that in PPM systems at the same transmission rate, the long synchronization sequence can be used in DPPM systems to achieve better performance than that of PPM systems.