Pil-Sang Yoon

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.

Adaptive fuzzy control of nonaffine nonlinear systems using Takagi-Sugeno fuzzy models

We present a control method for a general nonlinear systems using Takagi-Sugeno fuzzy models and develop an adaptation law to adjust the parameters of the fuzzy system. It is proved that the closed-loop system is stable in the sense of Lyapunov and all signals including tracking error, fuzzy parameters and estimate of upper bound for approximation error are bounded. Finally, simulation results verify the effectiveness of the proposed control method.

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.

Robustly stable fuzzy controller for uncertain nonlinear systems with unknown input gain sign

We propose and analyze a robust adaptive fuzzy controller for uncertain nonlinear systems without information on the input gain sign. The proposed scheme completely overcomes the singularity problem which occurs in the indirect adaptive feedback linearizing control. No projection in the estimated parameters and no switching in the control input are needed. The stability of the closed-loop system is guaranteed in the Lyapunov viewpoint.

Robust adaptive observer using fuzzy systems for uncertain nonlinear systems

This paper describes the design of a robust adaptive fuzzy observer for uncertain nonlinear dynamical system. The Lyapunov synthesis approach is used to guarantee a uniform ultimate boundedness property of the state estimation error, as well as of all other signals in the closed-loop system. Especially, we have focused on the realization of minimal dynamic order of the observer. For the purpose, we propose a new method in which no strictly proper (SPR) condition is needed and combine dynamic rule insertion scheme with on-line estimation of fuzzy parameters. No a priori knowledge of upper bounds on the optimal parameters and modeling errors is required. The theoretical results are illustrated through a simulation example.

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.

Optimal Design of Track Pattern for Holographic Read-Only Memory

An optimal track format for a holographic read-only-memory (ROM) disk is proposed that minimizes the intertrack crosstalk and stores conventional optical disk pit patterns with a density equivalent to that of digital versatile discs (DVDs) in a single holographic layer. To quantify the effect of intertrack crosstalk for the cases of variations in track width and pitch, we defined signal-to-crosstalk ratio (SCR) as a criterion to find the optimal track format. A numerical simulation is used to calculate SCR as a function of track width and pitch. The simulation results show that SCR varies with track width, pitch and pit length. When the track width, pitch, and minimum pit length are 0.5, 0.74, and 0.4 m, respectively, we can set a minimum pit length with a maximum SCR so that the storage density of each layer of the holographic ROM is equivalent to that of DVDs.