Jooyoun Park

A New Efficient Error Correctible Modulation Code for Holographic Data Storage

A new efficient modulation code for holographic memory, or 9:12 pseudo-balanced code(9-12PBC), has been developed and evaluated. The proposed code is partitioned into 16 codeword subsets and is decoded in conjunction with Viterbi algorithm. The results of numerical simulations and actual recording experiments show that 9-12PBC gives favorable trade-off between code rate and bit error rate(BER) performance.

A New Two-Dimensional Pseudo-Random Modulation Code for Holographic Data Storage

A new two-dimensional modulation scheme for holographic data storage, or complementary code-word block modulation (CCBM), and its decoding algorithm have been developed and evaluated. The CCBM constructs a pseudo-random array which provides a relatively uniform intensity distribution in the recording plane, leading to favorable SNR and BER performance.

Three-Dimensional Error Correction Schemes for Holographic Data Storage

Three-dimensional (3D) error correction coding (ECC) provides volumetrically coupled ECC blocks, the possible errors of which can be controlled powerfully by correcting errors from three different directions, iteratively. However, increased parities cause a large overhead, which limits the application of strong ECC schemes. In this study, a new efficient 3D ECC scheme and its decoding algorithm for holographic data storage were developed and evaluated. The proposed scheme has 3D ECC capability with a relatively low coding overhead, similarly to that of conventional 2D error correcting schemes, such as RSPC. It gives favorable ECC performance with a high efficiency in a page-based recording and retrieving system, which enables the use of a 3D ECC scheme for various applications.

Low-Density Parity-Check Code for Holographic Data Storage System with Balanced Modulation Code

In this report, we discuss low-density parity-check (LDPC) code for a holographic digital data storage (HDDS) system. In conventional LDPC decoding, the exact log likelihood ratio (LLR) value improves the error performance of the proposed LDPC code. A channel of an HDDS system has a nonlinear and complex characteristic. Therefore, it is difficult to obtain an exact probability model for an HDDS channel. In this study, an effective bit likelihood mapping method is developed and evaluated for LDPC decoding with a 6:8 balanced modulation code as a recording code. The LLR value, which represents the reliability of the 6:8 decision, is determined by considering demodulation error cases. An additional step is applied to a conventional LDPC decoding using feedback information in an iterative decoding in order to improve decoding performance. Feedback information can be helpful in accelerating the convergence of LDPC iterative decoding and in improving the error performance at the same number of decoding iterations. A simulation shows that the proposed algorithm scheme is effective and reliable.

A novel angle servo for holographic data storage system

A control method for the angle servo of reference beam during reading recoded data images of a holographic data storage system is presented. The recording scheme with track offset is adopted in order to verify the proposed angle servo. Using only recorded data tracks the angle error signal of reference beam is generated and the angle servo is implemented. Experiments have been performed on recording and reading data images to compensate Bragg angle mismatch.

A Modified Low-Density Parity-Check Decoder for Holographic Data Storage System

A modified low-density parity-check decoding scheme for holographic data storage has been developed and evaluated. It compensates the negative effect from neighboring pixels during the iterative decoding process, which improves the overall error-correction performance when pixels are misaligned. A simulation shows that the proposed scheme outperforms a conventional log-likelihood-ratio (LLR) belief-propagation (BP) algorithm.

Channel Data Retrieval in Page-Based Holographic Data Storage

A channel data retrieval scheme for page-based holographic data storage has been developed. It includes several signal-processing blocks for retrieving data reliably under noisy condition, namely, a frame grabber for capturing data adaptively in a rotating disk, a mark detector for tracing the data location, an equalizer for compensating interference, a two-dimensional modulation decoder for suppressing errors, and a three-dimensional error correction decoder for correcting errors generated by the holographic storage channel. The proposed scheme has been implemented with a field-programmable gate array chip and applied to actual data retrieval from holographic data storage. With the proposed channel data retrieval hardware, the user video data is successfully reconstructed from the holographic disk, which contains video data as holograms.

Iterative volumetric ECC schemes for holographic data storage

A new three-dimensional error correction coding (ECC) scheme for holographic data storage, or iterative volumetric ECC (IVECC), and its decoding algorithm have been developed and evaluated. The IVECC constructs volumetrically coupled ECC blocks, which can correct errors for three dimensions, leading to favorable ECC performance in page-based recording and retrieving system. It also can recover data of seriously corrupted pages or even missing pages by iterative decoding, may occur due to imperfect recording media or other defects on optical devices in holographic data storage.

Design and Implementation of a Hardware Channel Board for Holographic Data Storage

A channel board has been designed, manufactured, and used for real-time recording and reading processes. The channel coding and decoding algorithms were implemented on Xilinx field-programmable gate array (FPGA) devices. For fast data transmission between the channel board and personal computer (PC), a universal serial bus (USB) 2.0 interface is installed in the channel board. The firmware and device driver for USB interface achieved a transfer rate of 34 Mbyte/s. A holographic data storage system records a video stream, which was successfully retrieved and reconstructed without error.

Study for Bragg detuning effect and asymmetry of diffraction efficiency on the transmission and the reflection hologram

Bragg detuning effect and asymmetry of diffraction efficiency are serious problems if a photopolymer is used for the recording material of holographic storage. The critical reasons are bulk refractive index change and shrinkage of the recording materials. Until now, analyzing these effects bas been based on the K-sphere and the transmission hologram only or the reflection hologram only. A modified numerical model has been established explaining both holograms together and its results are well matched with experimental results. Bulk refractive index change causes + directional angle detuning on the transmission and reflection holograms. Material shrinkage leads to + directional angle detuning on the transmission hologram, but - directional angle detuning on the reflection hologram. The measured data are matched with Bragg detuning effect on the transmission and the reflection holograms with the proper the bulk refractive index change and shrinkage ratio of the material. For the asymmetry of diffraction efficiency, attenuated grating of material has also been considered. And asymmetries are reproduced on both holograms using absorption coefficient of attenuated grating.