Patent ID: 7900124

Claim:
A method for retrieving bits from a record carrier having the bits stored in marks in a two-dimensional pattern having a width of multiple rows of marks along a reading or writing direction of the two dimensional pattern, where more marks are distributed along a length of the rows than there are marks distributed across the width of the multiple rows, and where sampling the marks results in a sample of the signal waveform for a mark being affected by two dimensional intersymbol interference from adjacent marks, comprising the steps of: retrieving a sample; processing the sample using a trellis with a set of departure states and a set of arrival states, building up the trellis by converting each arrival state to a further departure state for use during a processing of the current sample, providing an output bit based on a backtracking operation or trace-back operation along the trellis over a certain backtracking depth, characterized in that the states of the trellis are constructed from the two-dimensional pattern by retrieving each subsequent sample corresponding to an adjacent mark from an adjacent row, that the trellis is a one dimensional trellis, and that each subsequent sample is used as an input for the one dimensional trellis where the two dimensional array of marks is delineated by a boundary row comprising an a priori known boundary information, said a priori boundary information being a forced zero and where the one dimensional trellis is a time variant one dimensional trellis extended with a single branch for each of the forced zeros.