Holographic Data Storage System Research Articles

Tilt Servo Control by Intelligent Algorithm in Holographic Data Storage System

Tracking servo and tilt servo control are very important research in holographic data storage system. In this paper, we propose intelligent servo control by fuzzy rules in holographic data storage system. Hence, we have found pattern of tilt servo control in holographic data storage system through fuzzy system. Fuzzy rules were generated by subtractive clustering algorithm for controlling tilt servo. Therefore, we control tilt servo using fuzzy rules in holographic data storage system. Consequently, practical pattern of tilt servo control was found by intelligence algorithm in holographic data storage system.

A Simple 2/3 Modulation Code for Multi-Level Holographic Data Storage

We propose a simple 2/3 modulation code for multi-level holographic data storage (HDS). HDS is a promising method for the optical data storage system. However, two-dimensional (2D) inter-symbol interference (ISI) and inter-page interference (IPI) are weaknesses of HDS systems. Moreover, if multi-level symbols are stored, such systems are more vulnerable to errors. A modulation code can be used to alleviate these problems. Therefore, we introduce a simple 2/3 modulation code for multi-level HDS systems, which is simple and mitigates 2D ISI patterns.

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.

Two-Dimensional Soft Output Viterbi Algorithm with a Variable Reliability Factor for Holographic Data Storage

In a practical holographic data storage system, the reconstruction process for a data page should account for the processing time as well as the bit error rate (BER) performance. To improve both aspects, we introduce two-dimensional (2D) partial response maximum likelihood composed of a 2D partial response (PR) target including diagonal elements and a 2D soft output Viterbi algorithm (SOVA) with a variable reliability factor. The 2D SOVA performs two one-dimensional (1D) SOVAs in structural accordance with the 2D PR target where extrinsic information uses the expected value calculated on a synchronization pattern. Finally, the 2D SOVA exports a weighted average using the reliability factor that is updated similarly as the optimization scheme for each page. The simulation results show that the proposed method has superior BER performance, despite using only two 1D SOVAs as compared with the modified 2D SOVA composed of four 1D SOVAs.

Digital Image Diffusion Technique for Suppressing Interpage Crosstalk in Holographic Data Storage

To suppress interpage crosstalk that strongly restricts holographic data storage capacity, a digital image diffusion technique was proposed. In this technique, signal and crosstalk components are separated from the propagation angle difference produced by using a random diffuser and the nature of phase conjugate lights. The most attractive feature of the technique is that crosstalk suppression can be conducted while mostly keeping the conventional holographic data storage system unchanged by integrating optical processing and digital processing effectively. The connection between the two types of processing is realized by using two spatial light modulators for complex amplitude generation and phase detection methods for complex amplitude measurement. The simulation results showed that the proposed technique could increase the recording density 5.5-fold and reduce the shift pitch by a factor of 5 in comparison with conventional multiplexing methods when the diffusion angle of the diffuser is 10°.

정수계획법 모형을 이용한 홀로그래픽 저장장치의 DC-억압 GS코딩의 성능평가

광저장장치의 DC-억압을 위한 멀티모드 코딩 기법 중 Guided Scrambling (GS) 코딩기법이 널리 사용된다. 홀로그래픽 저장장치를 위한 DC-억압 GS코딩에서는 후보코드 선택기준으로 심볼의 균등한 분포 및 심볼간 천이의 최대화 기준이 고려되었다. 본 연구에서는 후보코드행렬의 digital sum value (DSV)의 <TEX>$l_{\infty}$</TEX>-norm을 최소화하는 minimum DSV (MDSV) 기준 GS코딩을 정수계획법 모형으로 수식화하고, 제안된 모형을 사용하여 MDSV 기준과 최대천이강도 기준이 적용된 GS코딩의 성능을 제어비트수, 행렬크기 및 스크램블링 다항식들의 조합에 대하여 평가한다. For the DC-free encoding of source data, the Guided Scrambling (GS) technique is widely used as multi-mode coding in the optical data storage system. For DC-suppression GS coding in the holographic data storage system, the conservative array and balanced coding criteria are proposed. In this paper, equivalent integer programming models are developed to determine the optimal control bits for the minimum digital sum value (MDSV), conservative array, and balanced coding criteria. Using the proposed integer programming models, we compare the performance of GS encoding for the various combination of control bit/array sizes and scrambling polynomials.

Hardware implementation of pixel detection in gray-scale holographic data storage systems

This paper presents hardware implementation of an efficient solution to recovering gray-scale data pixels of images that have undergone interpixel interference in holographic data storage systems. The adopted algorithm, called the turbo receiver using interference-aware dual-list (TRIDL) detection, enjoys benefits of low error rate performance and low complexity. To verify the functionality and feasibility, this paper implements TRIDL detection with some circuit design techniques such as resource sharing on a field-programmable gate array.

Turbo Equalization Scheme between Partial Response Maximum Likelihood Detector and Viterbi Decoder for 2/4 Modulation Code in Holographic Data Storage Systems

A turbo equalization scheme for holographic data storage (HDS) systems is proposed. The proposed turbo equalization procedure is conducted between a one-dimensional (1D) partial response maximum likelihood (PRML) detector and the joint Viterbi decoder by exchanging a priori and extrinsic information. In the joint Viterbi decoder, the modulation and convolutional decoding is performed simultaneously by mapping a 2/4 modulation symbol onto the trellis of the convolutional code to reduce the complexity of the decoding procedure and improve the decoding capability for the iterative equalization and decoding. In addition, since the channel model is described as the two-dimensional convolution in HDS systems, the 1D PRML detector is performed in the vertical direction and the joint Viterbi decoder is performed in the horizontal direction to maximize the performance gains. The simulation result shows that the proposed turbo equalization scheme has the better bit error rate performances as the number of iterations increases.

Turbo Equalization Scheme between Partial Response Maximum Likelihood Detector and Viterbi Decoder for 2/4 Modulation Code in Holographic Data Storage Systems

A turbo equalization scheme for holographic data storage (HDS) systems is proposed. The proposed turbo equalization procedure is conducted between a one-dimensional (1D) partial response maximum likelihood (PRML) detector and the joint Viterbi decoder by exchanging a priori and extrinsic information. In the joint Viterbi decoder, the modulation and convolutional decoding is performed simultaneously by mapping a 2/4 modulation symbol onto the trellis of the convolutional code to reduce the complexity of the decoding procedure and improve the decoding capability for the iterative equalization and decoding. In addition, since the channel model is described as the two-dimensional convolution in HDS systems, the 1D PRML detector is performed in the vertical direction and the joint Viterbi decoder is performed in the horizontal direction to maximize the performance gains. The simulation result shows that the proposed turbo equalization scheme has the better bit error rate performances as the number of iterations increases.

Error Correcting Capable 2/4 Modulation Code Using Trellis Coded Modulation in Holographic Data Storage

An error correcting capable 2/4 modulation code scheme is proposed in holographic data storage (HDS) systems. We adopt trellis coded modulation (TCM) to obtain a good error correcting capability without loss of data rate in the HDS systems. To overcome loss of a data rate caused by a 1/2-rate convolutional code, we extend a 2/4 modulation code set the 3/4 modulation code set as high-order modulation in the proposed scheme. Additionally, we find an optimal mapping method of index numbers to maximize the free distance on the trellis and calculate the free distance according to each constraint length. The simulation results show that the proposed scheme with the same data rate has about 4 dB coding gains compared to the conventional 2/4 modulation coding scheme.

Soft-Decision Viterbi Decoding Scheme and a New Reliability Metric for 4/6 Modulation Code in Holographic Data Storage

A soft-decision Viterbi decoding for a 4/6 modulation code is proposed in a holographic data storage system. Since the previous proposed soft-decision Viterbi decoding does not support a higher rate modulation codes than 1/2 rate modulation codes, we propose a new reliability metric to support the 4/6 modulation code. The reliability metric is used to calculate the branch metric on the trellis. For a better coding gain, we find a symbol mapping method for the modulation code which provides a large free distance on the trellis to have the enhanced error correcting capability. Simulation results show that the proposed scheme has about 2 dB coding gains than the conventional soft-decision Viterbi decoding scheme.

Soft-Encoding Scheme of 3/4 Tone-Controllable Code for Channel Iteration of Low-Density Parity-Check Code on the Holographic Data Storage

In turbo equalization for holographic data storage (HDS) systems, an iterate-back signal must pass through a modulation coding process for channel iteration since the iterate-back signal is a demodulated signal and the input of a detector is modulated data. Also, the iterate-back signal is a soft-value, so the soft-input and soft-output (SISO) must be treated by a modulation code. A 3/4 tone-controllable (TC) code can control the ratio of ON and OFF pixels on each data page. The memory capacity of a holographic data storage system can be increased if we use a TC code. In this paper, we concatenate a 3/4 TC code and LDPC code, and then simulate the turbo equalization performance on a HDS channel. A SISO 3/4 TC code is needed for this simulation. Therefore, we propose a soft-encoding scheme for a SISO 3/4 TC code.

Sequential Two-Dimensional Partial Response Maximum Likelihood Detection Scheme with Constant-Weight Constraint Code for Holographic Data Storage Systems

A sequential two-dimensional (2D) partial response maximum likelihood (PRML) detection scheme for holographic data storage (HDS) systems is proposed. We use two complexity reduction schemes, a reduced-state trellis and a constant-weight (CW) constraint. In the reduced-state trellis, the limited candidate bits surrounding the target bit are considered for the 2D PRML detector. In the CW constraint, the trellis transitions that violate the CW condition that each code-word block has only one white bit are eliminated. However, the 2D PRML detector using the complexity reduction schemes, which operates on 47 states and 169 branches, has performance degradation. To overcome performance degradation, a sequential detection algorithm uses the estimated a priori probability. By the sequential procedure, we mitigate 2D intersymbol interference with an enhanced reliability of the branch metric. Simulation results show that the proposed 2D PRML detection scheme yields about 3 dB gains over the one-dimensional PRML detection scheme.

Two-Dimensional Equalization Using Bilinear Recursive Polynomial Model for Holographic Data Storage Systems

In this paper, we propose new two-dimensional (2D) nonlinear equalizers developed on the basis of a bilinear recursive polynomial (BRP) model for holographic data storage (HDS) systems. The 2D BRP equalizer (BRPE) and the 2D BRP decision feedback equalizer (BRPDFE) are proposed. The bit error rate (BER) performances of the proposed schemes are studied in the electrical-noise-dominant channel (ENDC) and the optical-noise-dominant channel (ONDC). The proposed schemes are compared with the conventional adaptive DFE and the partial response maximum likelihood (PRML) detector. The simulation results show that the proposed schemes outperform the adaptive DFE and the PRML detector. In particular, the BRPDFE shows the best BER performance in both the ENDC and the ONDC.

Effective Two-Dimensional Partial Response Maximum Likelihood Detection Scheme for Holographic Data Storage Systems

An effective two-dimensional (2D) partial response maximum likelihood (PRML) detection scheme for holographic data storage (HDS) systems is proposed. The proposed scheme adopts the simplified trellis diagram, uses a priori information, and detects the data in two directions from the previously proposed detection schemes. The simplified trellis diagram which has 4 states and 8 branches yields a dramatic complexity reduction while the simplified 2D PRML detector shows serious performance degradation in the high density HDS channels. To prevent performance degradation, the proposed detector uses a priori information in order to give higher reliability to the branch metric. Furthermore, the proposed scheme detects the data in the vertical and horizontal directions to fully utilize the characteristics of the channel detection with a 2D partial response target. By effective combination of these three techniques, the proposed scheme with a simple structure has more than 2 dB gains compared to the conventional detection schemes.

Effective Two-Dimensional Partial Response Maximum Likelihood Detection Scheme for Holographic Data Storage Systems

An effective two-dimensional (2D) partial response maximum likelihood (PRML) detection scheme for holographic data storage (HDS) systems is proposed. The proposed scheme adopts the simplified trellis diagram, uses a priori information, and detects the data in two directions from the previously proposed detection schemes. The simplified trellis diagram which has 4 states and 8 branches yields a dramatic complexity reduction while the simplified 2D PRML detector shows serious performance degradation in the high density HDS channels. To prevent performance degradation, the proposed detector uses a priori information in order to give higher reliability to the branch metric. Furthermore, the proposed scheme detects the data in the vertical and horizontal directions to fully utilize the characteristics of the channel detection with a 2D partial response target. By effective combination of these three techniques, the proposed scheme with a simple structure has more than 2 dB gains compared to the conventional detection schemes.

Two-Dimensional Equalization Using Bilinear Recursive Polynomial Model for Holographic Data Storage Systems

Two-Dimensional Equalization Using Bilinear Recursive Polynomial Model for Holographic Data Storage Systems

Sequential Two-Dimensional Partial Response Maximum Likelihood Detection Scheme with Constant-Weight Constraint Code for Holographic Data Storage Systems

Sequential Two-Dimensional Partial Response Maximum Likelihood Detection Scheme with Constant-Weight Constraint Code for Holographic Data Storage Systems

Two-Dimensional Iterative Decoding Schemes for Holographic Data Storage Systems

Two-Dimensional Iterative Decoding Schemes for Holographic Data Storage Systems

Two-Dimensional Iterative Decoding Schemes for Holographic Data Storage Systems

Two iterative decoding (ID) schemes, which are the ID using a single parity bit (ID-SPB) and ID using a modulation code (ID-MC), are proposed for holographic data storage systems. In the ID-SPB, a single two-dimensional parity bit is employed to conduct ID, whereas in the ID-MC, the inherent constraint of the modulation code is utilized to conduct ID. In both schemes, a data page is iteratively decoded by exchanging extrinsic information between the horizontal and vertical data bits in the page. In particular, in the ID-SPB, by adding more parity bits to each row and column of the interleaved page, we can conduct the ID within a page as well as between the original and interleaved pages. Thus, additional performance gain can be achieved in the ID-SPB. On the other hand, the ID-MC has a performance gain without loss of data rate since parity bits are not required for ID. The simulation results show that the proposed ID-SPB and ID-MC have about 2–4 and 1–2 dB performance gains in terms of bit error rate compared with the system without ID, respectively.