Low-Density Parity-Check Coding for Holographic Data Storage

Since the signal-to-noise ratio (SNR) of a holographic storage system is one of the dominant factors that determine the recording capacity, an improvement in SNR is crucial to the achievement of a high recording capacity. We therefore applied a low-density parity-check (LDPC) code and its soft iterative decoding to a holographic storage system. We examined the bit error rate (BER) performance by simulation and experiment, using the LDPC code as an error correction code and a 2:4 modulation code as a recording code. The simulation revealed that the LDPC code shows an SNR improvement of 5.3 dB and a coding gain of 4.8 dB at a BER of 1×10-5. The experiment indicated that an LDPC decoder completely corrects bit errors in a signal, which is reproduced from a recorded hologram, with an SNR of 12.5 dB and a raw BER of 1.3×10-2. The LDPC coding is thus effective in achieving a high recording capacity.