<title>Likelihood-based error correction for holographic storage systems</title>

Abstract

ABSTRACT We consider a volume holographic memory (VHM) system that is corrupted by interpixel interference (IPI) and detector noise. We compare hard-decision Reed-Solomon (RS) decoding with both hard- and soft- decision algorithms for 2D array decoding. RS codes are shown to provide larger VHM storage capacity and density as compared with array codes when hard-decision methods are employed. A new likelihood-basedsoft-decision algorithm for 2D array decoding is described. The new decoding algorithm is motivated byiterative turbo-decoding methods and is capable of incorporating a priori knowledge of the corrupting IPIchannel during decoding. The new algorithm is shown to offer VHM capacity and density performance superior to hard-decision RS methods. Keywords: optical memory, holography, error correction, turbo coding 1. INTRODUCTION The potential advantages of volume optical storage were recognized almost 30 years ago and sincethat time many research efforts have focused on improving the underlying materials and devices for usein such systems.111 Recent progress in these supporting technologies have made possible several system-level demonstrations of volume optical storage. These recent demonstrations have verified the feasibility ofvolume memory systems for offering large volumetric storage capacities, fast access times, and very highdata transfer rates realized via the parallel two-dimensional (2D) nature of the stored data. The successof these volume storage testbeds has served to ignite additional research into supporting two-dimensionalor page-oriented interface technologies such as parallel 2D data detection and error correction.127' Thevolume holographic memory (VHM) application therefore provides a strong impetus to study traditional