MAXIMUM-LIKELIHOOD SYMBOL SYNCHRONIZATION FOR THE DIRECT-DETECTION OPTICAL ON-OFF-KEYING CHANNEL
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abstract
The maximum-likelihood symbol synchronization statistic is derived from noisy observations of randomly modulated on-off-keying data for the direct-detection optical channel. A similar statistic for the case when the transmitter sends a special pattern of alternating 0s and ls for synchronization purposes only is also derived. Various approximations to the optimal statistic are introduced and their performance compared to the optimal one under a new criterion, believed to be more appropriate for the Poisson channel than the mean-square error criterion routinely used with other channels. It is shown that although the variable associated with symbol transitions is continuous, the possible values of it that maximize the maximum-likelihood (ML) statistic belong to a discrete set with relatively few elements. 1987 IEEE