Two-Dimensional Soft Output Viterbi Algorithm Research Articles

Soft-information flipping scheme based on a priori LLRs summation for ultra-high density magnetic recording

Inter-track interference (ITI) is the main problem in high areal density (AD) of magnetic recording systems such as bit-patterned magnetic recording (BPMR) technology thus the ITI avoidance scheme is the way to improve the performance of the recording system. Two-dimensional (2D) modulation codes i.e., the rate-5/6 2D modulation code, was proposed to avoid the severe ITI effect which can successfully improve the system performance when it was considered without the codeword border effect. However, when we have to consider the codeword border effect, some upper and lower tracks cannot avoid ITI because both of them still be interfered from their sidetracks. To improve this weakness, a rate-5/6 2D modulation code was combined with the bit-flipping technique based on the normalization criteria of the two-dimensional soft-output Viterbi algorithm (2D-SOVA). Although, the bit-flipping technique can improve the performance of all tracks; however, the gain optimization is difficult to describe the relationship of the soft-information flipping technique. Therefore, this research proposes a novel of soft-information flipping scheme to describe the bit-flipping technique based on a priori log-likelihood ratios of the rate-5/6 encoding constraint in BPMR system. The simulation results clearly indicate that, at the same user density, the proposed system can provide bit-error-rate performance gain over the other recording systems in both of with and without position jitter noise.

An ant colony optimization aided two-dimensional soft output viterbi algorithm detection scheme for holographic data storage systems

In this paper, we propose an ant colony optimization (ACO) aided two-dimensional (2D) soft output Viterbi algorithm (SOVA) detection scheme for holographic data storage systems. The proposed detection scheme adopts the conventional 2D SOVA detection scheme which has two one-dimensional (1D) SOVA detectors for the horizontal and vertical directions, and employs an ACO detector with a reliability test. The proposed detection scheme operates in two stages. In the first stage, the data is detected by conducting the 2D SOVA detection scheme for the horizontal and vertical directions. In the second stage, the reliability test is taken to detect the less reliable bits in a data page by using the outputs of the horizontal and vertical 1D SOVA detectors from the first stage. If the less reliable bits are detected, the ACO detector is performed to improve the reliability of the unreliable bits. Otherwise, the sum of outputs from the horizontal and vertical 1D SOVA detectors is detected by a threshold detector. The bit error rate performances of the proposed detection scheme are compared to the conventional detection schemes. Simulation results show that the proposed detection scheme performing the ACO detector for only 0.3% of bits has more than 7 dB gains compared to the conventional 2D SOVA detection scheme when the grade of blur is 1.8.

Data page reconstruction method based on two-dimensional soft output Viterbi algorithm with self reference for holographic data storage

This study introduces a two-dimensional (2D) partial response maximum likelihood (PRML) method to reconstruct a degraded data page having 2D inter-symbol interference for holographic data storage. The proposed 2D PRML method consists of 2D partial response (PR) target, 2D equalizer using least mean square algorithm, and 2D soft output Viterbi algorithm (SOVA) having just two one-dimensional (1D) SOVAs in horizontal and vertical directions. To accurately organize a trellis diagram of the 1D SOVA in structural accordance with the 2D PR target, this study proposes the self-reference process for the extrinsic information in the 1D SOVA. Finally, simulation results show that the proposed method has bit error rate performance similar to that of modified 2D SOVA having four 1D SOVAs despite the relatively low computational complexity. Moreover, parallel processing is possible in the two 1D SOVAs through the self-reference process.

Performance Improvement Using Iterative Two-Dimensional Soft Output Viterbi Algorithm Associated with Noise Filter for Holographic Data Storage Systems

Demand of the data storage becomes more and more growing. This requests the next generation of storage devices to have the dominated storage capability associated with superfast read/write rate. Holographic data storage (HDS) is investigated for a long time and is considered to be a candidate for the future storage system. However, it has two-dimensional intersymbol interference that conventional one-dimensional detection solutions have not yet handled strictly because of the complexity level of system as well as the cost. We propose a new scheme that combines iterative soft output Viterbi algorithm with noise filter for improving the bit error rate performance of HDS.

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.

Two-Dimensional Soft Output Viterbi Algorithm With Dual Equalizers for Bit-Patterned Media

This study proposes a two-dimensional (2D) detection method using partial response maximum likelihood (PRML) for bit-patterned media (BPM) storage. Because the readback signals are deteriorated by 2D channel effect, that is, intersymbol interference along the track direction and intertrack interference across the track direction, it is necessary to use “2D” PRML in order to improve the bit error rate (BER) performance. The 2D PRML in the proposed method is based on the 2D soft output Viterbi algorithm (SOVA), which is composed of two one-dimensional SOVAs. In addition, we propose a 2D SOVA for a 2D partial response (PR) target using dual equalizers: one estimates the correlated signal (output data of the PR target), used as the main information with encoding rule, and the other estimates the binary signal (binary data recorded on BPM), used as extrinsic information on the other direction's neighboring bits. The simulation results show that the proposed method improves the BER performance at a low computational complexity.

홀로그래픽 저장장치를 위한 2차원 SOVA 성능 비교

본 논문에서는 홀로그래픽 저장장치를 위한 2차원 검출기인 2차원 SOVA와 반복 검출 2차원 SOVA의 검출 성능을 비교하였다. 홀로그래픽 저장장치는 2차원 인접심볼간 간섭이 있는 채널을 가지고 있어서 2차원 검출기를 사용하여야 검출 성능이 좋다. 2차원 SOVA와 반복 검출 2차원 SOVA는 2차원 인접심볼간 간섭이 있는 채널에서 잘 동작하는 검출기이다. 이 두가지 검출기를 분석하고 성능을 비교해 보았다. 2차원 SOVA는 1차원 검출기에 비해 약 2 dB의 성능이득이 있었고, 반복 검출 2차원 SOVA는 2차원 SOVA에 비해 약 1 dB 정도의 성능 이득이 있었다. 반대로, 반복 검출 2차원 SOVA는 2차원 SOVA에 비해 약 2배 정도 복잡도가 늘어나며, 2차원 SOVA도 1차원 검출기에 비해 약 2배 정도 복잡도가 늘어난다. We introduce two-dimensional soft output Viterbi algorithm (2D SOVA) and iterative 2D SOVA for holographic data storage. Since the holographic data storage is 2D intersymbol interference (ISI) channel, the 2D detection schemes have good performance at holographic data storage. The 2D SOVA and iterative 2D SOVA are 2D detection schemes. We introduce and compare the two 2D detection schemes. The 2D SOVA is approximately 2 dB better than one-dimensional (1D) detection scheme, and iterative 2D SOVA is approximately 1 dB better than the 2D SOVA. In contrast, the iterative 2D SOVA is approximately twice complex higher than 2D SOVA, and 2D SOVA is approximately twice complex higher than 1D detection scheme.

Modified Two-Dimensional Soft Output Viterbi Algorithm with Two-Dimensional Partial Response Target for Holographic Data Storage

The previously modified two-dimensional (2D) soft output Viterbi algorithm (SOVA) for holographic data storage (HDS) consists of four one-dimensional (1D) SOVAs in accordance with two different 1D partial response (PR) targets (vertical and horizontal directions). In this study, we propose a detection method in structural accordance with a 2D PR target through the use of the modified 2D SOVA. The proposed method shows superior bit error rate performance owing to the use of a 2D PR target that contains more information than the 1D PR target. Moreover, a reduction in power consumption, computational complexity, and the system-on-chip size for HDS system can be expected as a result of the use of only one 2D equalizer.

Modified Two-Dimensional Soft Output Viterbi Algorithm with Two-Dimensional Partial Response Target for Holographic Data Storage

Modified Two-Dimensional Soft Output Viterbi Algorithm with Two-Dimensional Partial Response Target for Holographic Data Storage

Iterative Decoding between Two-Dimensional Soft Output Viterbi Algorithm and Error Correcting Modulation Code for Holographic Data Storage

We propose an iterative decoding scheme for holographic data storage that uses modulation codes with a trellis structure to obtain some coding gain. Furthermore, the iterative scheme between a channel detector and the modulation code can achieve more coding gain. In the simulation, when there are (10%, 10%) and (20%, 20%) misalignments, the proposed iterative scheme with a pseudorandom interleaver performs approximately 0.3 and 1 dB better, respectively, compared to the scheme without iteration.

Iterative Decoding between Two-Dimensional Soft Output Viterbi Algorithm and Error Correcting Modulation Code for Holographic Data Storage

Iterative Decoding between Two-Dimensional Soft Output Viterbi Algorithm and Error Correcting Modulation Code for Holographic Data Storage

Two-dimensional soft output Viterbi algorithm with noise filter for patterned media storage

We introduce a two-dimensional (2D) soft output Viterbi algorithm (SOVA) using two 1D SOVAs, which apply two noise filters corresponding to horizontal and vertical directions, respectively, for patterned media storage. Patterned media storage has 2D intersymbol interference (ISI), which includes ISI from neighboring symbols and intertrack interference from adjacent tracks, since there is a small space between adjacent tracks and neighborhood symbols. Noise filter replaces colored noise with white noise. As a result, the noise filter can reduce the noise power, so that performance can be improved. As shown in the simulation results, when there is no off-track, the 2D SOVA using a noise filter is approximately 0.4 dB better than not using a noise filter at a 10−6 bit error rate; when there is 20% off-track, it has about a 1 dB gain.

Iterative Two-Dimensional Soft Output Viterbi Algorithm for Patterned Media

We introduce an iterative two-dimensional (2-D) soft output Viterbi algorithm (SOVA) for patterned media storage. Patterned media storage has enormous 2-D intersymbol interference (ISI), which includes ISI from neighboring symbols and intertrack interference (ITI) from adjacent tracks, since there is a small space between adjacent tracks and neighboring symbols. Thus, conventional one-dimensional (1-D) detection schemes have difficulty overcoming the 2-D ISI problem. To combat 2-D ISI, it is natural to consider a 2-D detection scheme. Since the complexity of pure 2-D Viterbi detection is quite high, we propose a 2-D SOVA using two 1-D SOVAs. We also propose an iterative scheme between two 1-D SOVAs to achieve its best performance without error correcting codes.

Modified Two-Dimensional Soft Output Viterbi Algorithm for Holographic Data Storage

We propose an alternate two-dimensional soft output Viterbi algorithm (2D SOVA) for holographic data storage. The proposed 2D SOVA uses a one-dimensional (1D) SOVA for both the horizontal and vertical directions. The 1D SOVA detects each direction with extrinsic information on the other direction's 1D SOVA. This proposed 2D SOVA has a better performance than a conventional 2D SOVA in terms of output bit error rate.

Two-Dimensional SOVA and LDPC Codes for Holographic Data Storage System

We introduce partial response maximum likelihood (PRML) with the two-dimensional (2D) soft output Viterbi algorithm (SOVA) and 2D equalizer for holographic data storage (HDS) channel. The 2D SOVA output is the average of two 1D SOVAs that are separately operated in horizontal and vertical directions. The complexity of the proposed 2D SOVA is increased only twice compared with 1D SOVA while its performance is superior to that of 1D SOVA. Since the 2D SOVA outputs soft decision value, LDPC can be utilized by the soft-in hard-out decoding. We study for different PR target, comparing 1D Viterbi detection with 2D SOVA detection, different misalignments, and two kinds of LDPC codes.

Partial Response Maximum Likelihood Detections Using Two-Dimensional Soft Output Viterbi Algorithm with Two-Dimensional Equalizer for Holographic Data Storage

We present partial response maximum likelihood (PRML) detection with two-dimensional (2D) equalizer scheme and introduce 2D soft output Viterbi algorithm (SOVA) detection for holographic data storage (HDS) channel. We also propose the 2D PR target for the HDS channel varying the grade of blur. Simulation results show that the proposed schemes outperform the nearest neighbor detection.