SYNCHRONIZABLE CODES FOR THE OPTICAL OPPM CHANNEL

Random overlapping pulse-position modulation (OPPM) sequences result i n an unrecoverable error floor on both the probability of erroneous sy nchronization and the probability of symbol error when only chip synch ronization is present. It is known, however, that for a given sequence length M, a subset of the set of all possible sequences is synchroniz able in the sense that in the absence of noise, the receiver can corre ctly symbol synchronize by observing M or more symbol intervals. In th is paper we design finite-state machines and codes over a J-ary alphab et, which produce sequences with the property that every subsequence o f length L is synchronizable. Some of the codes, in addition to being synchronizable, produce a coding gain. For an optical Poisson channel we introduce joint synchronization and detection algorithms that utili ze the memory in the encoded sequences to produce joint estimates of t iming and sequences. Their performance is analyzed through simulations and analytical results.