CODING FOR THE UNSYNCHRONIZED OPTICAL OPPM CHANNEL
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Random OPPM sequences result in an unrecoverable error floor on both the probability of erroneous synchronization and the probability of symbol error when only chip synchronization is present. It is known, however, that for a given sequence length M, a subset of the set of all possible sequences is synchronizable in the sense that in the absence of noise, the receiver can correctly symbol-synchronize by observing M or more symbol intervals. In this paper we design finite state machines and codes over a J-ary alphabet which produce sequences with the property that every subsequence of length L is synchronizable and introduce algorithms that utilize the memory in the encoded sequences to produce joint estimates of timing and sequences.
