Soft-Decision Viterbi Decoding for 2/4 Modulation Code in Holographic Memory

The signal quality of holographic memory is lowered by the thermal noise and shot noise of a detector, and the reproduced image distortion caused by the shrinkage of a medium. For the improvement of signal quality, soft-decision Viterbi decoding was performed after 2/4 modulation coding. For the 2/4 modulation code, a new two-dimensional reliability was defined. A method of soft-decision Viterbi decoding, which uses this reliability as the value for soft decision, was proposed. In our record/reproduction experiment using this method, the reduction in bit error rate and effectiveness of soft-decision Viterbi decoding were verified.