Iterative row-column-file soft decision feedback equalizer for three-dimensional intersymbol interference channels

This paper presents a three-dimensional intersymbol interference (ISI) equalization algorithm employing turbo equalization for detection of 3D binary images in holographic storage systems. The algorithm scans the 3D received image along rows, columns, and files, and iteratively exchanges weighted soft information between maximum a posteriori (MAP) detectors for each scan direction until convergence is achieved. Each MAP detector exploits soft decision feedback from previously processed rows, columns, or files. An EXIT chart technique is proposed for efficient optimization of the weights applied to the log-likelihood ratios exchanged between MAP detectors. On the 2 × 2 × 2 averaging-mask channel, the proposed algorithm achieves performance within 2.0 dB of the maximum likelihood performance bound. The MAP detectors may be updated in parallel at little cost in system performance, allowing parallel implementation for increased execution speed.