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Abstract

Due to code constraints and pickup limitations of optical pickups, much of the signal energy of a binary coded analog signal, and therefore much of the information content, has dissipated at frequencies above about one-half (or even above about one-fourth) of the sampling frequency f.sub.s. For example, the response of data streams from DVD layers falls off by about 40 dB by f.sub.s/4 while the response of a CD data stream falls off by about 18 dB by f.sub.s/4. Thus, a data channel is provided in which the sampling rate f.sub.s is less than the channel bit rate f.sub.b. The data channel may be part of an optical storage drive in which data has been RLL encoded at d.gtoreq.0 and the sampling rate may be one-half the channel bit rate. Preferably, a sequence detector is employed which outputs two channel bits for each input sample.

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