NEAR-OPTIMAL PARALLEL DISTRIBUTED DATA DETECTION FOR PAGE-ORIENTED OPTICAL MEMORIES

Volume optical storage systems suffer from numerous sources of noise a nd interference, the effects of which can seriously degrade retrieved data fidelity and produce unacceptable bit-error rates (BER's), We exa mine the problem of reliable two-dimensional data retrieval in the con text of recently developed soft-decision methods for iterative decodin g. We describe a novel near-optimal algorithm in which each pixel on t he page is treated as a starting point for a simple iterative procedur e so that a highly parallel, locally connected, distributed computatio nal model emerges whose operation is well suited to the page-oriented memory (POM) interface format. We study the use of our two-dimensional distributed data detection (2D(4)) algorithm with both incoherent (li near) and coherent (nonlinear) finite-contrast POM channel models. We present BER results obtained using the 2D4 algorithm and compare these with three other typical methods [i.e., simple thresholding (THA), di fferential encoding (DC) and the decision feedback Viterbi algorithm ( DFVA)]. The BER improvements are shown to have a direct impact on POM storage capacity and density and this impact is quantified for the spe cial case of holographic POM, In a Rayleigh resolved holographic POM s ystem with infinite contrast, we find that 2D(4) offers capacity impro vements of 84%, 56%, and 8% as compared with DC, THA, and DFVA respect ively, with corresponding storage density gains of 85%, 26%, and 9%, I n the case of finite contrast (C = 4), similar capacity improvements o f 93%, 18%, and 4% produce similar density improvements of 98%, 21%, a nd 6%, Implementational issues associated with the realization of this new distributed detection algorithm are also discussed and parallel n eural and focal plane strategies are considered, A 2 cm(2) lambda = 0. 1 mu m digital VLSI real estate budget will support a 600 x 600 pixel 2D(4) focal plane processor operating at 40 MHz with less than 1.7 W/c m(2) power dissipation.