A 6/9 Four-Ary Modulation Code for Four-Level Holographic Data Storage

A holographic data storage (HDS) system can provide high storage capacity, faster transmission, and shorter access time. However, there are two major concerns with such systems: two-dimensional (2D) inter-symbol interference (ISI) and inter-page interference (IPI). The use of existing partial response maximum likelihood (PRML) detection can somewhat mitigate the problem of ISI. However, if the channel is subject to misalignment, the performance of PRML detection can be degraded. This problem can be remedied by a modulation code. Thus, this paper proposes a 6/9 modulation code, which mitigates ISI, and a modulation/demodulation scheme.