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Symbol discriminator for high-density multilevel recording

We consider the design and analysis of read-back symbol discriminator for multilevel codes on an electron trapping optical memory recording channel. The linear amplitude response of this new media provides a method of increasing the density of stored data by using multilevel or M-ary runlength limited (RLL) channel codes. In this paper, we consider the problem of symbol detection for a high density M-ary channel that encodes 3 user data bits per minimum sized feature to achieve a maximum channel capacity of 3.4 bits/sec/Hz. A dynamic model of the optical/electronic read channel is constructed to generate the expected amplitude waveform. These signals are discriminated by a maximum likelihood detector that operates on a small number of quantized amplitude values. Another model is constructed to study the effect of signal amplitude quantization on the error performance for M-ary RLL channel codes. Included in the analysis are the effects due to variations in the offset of both sampling phase and amplitude levels. Comparisons of the proposed symbol detection method are presented for two different M-ary RLL channels operating at user data rates from 25 Mbits/sec to 68 Mbits/sec.