Two-Dimensional Interference Estimator with Parallel Structure for Holographic Data Storage Channel

Round 1

Reviewer 1 Report

This paper proposes a two-dimensional (2D) interference estimator to prevent the 2D inter-symbol interference (ISI) and an equalizer with 2D generalized partial response maximum likelihood. The argument of this paper is clear, and the results support the conclusion. On the other hand, I think some points are not fully explained, and the paper would be improved by correcting the following points.

 

Major concerns

1. The process of deriving Eqs (18)-(20) from the Lagrange function (17) based on the first-order condition should be described in more detail for readers.
2. Symmetrical shape is assumed as the general partial response (GPR) target G, but the validity of this assumption needs to be discussed.
3. The effect of the fill factor is evaluated only for the case of α= 1 in this paper but should be evaluated for other conditions if possible.
4. The HDS channel is shown in Eq. (36), but since HDS usually detects light intensity, the right-hand side of Eq. (36) seems to be appropriate for absolute squared. There is a need for discussion on this point.
5. The performance of the proposed method is with the 2D soft-output Viterbi algorithm (SOVA) and decision feedback equalizer (DFE) in Fig. 4 and 5. Besides SOVA and DFE, linear and quadratic minimum mean squared error (LMMSE, QMMSE) equalizer [1, 2], adaptive Volterra equalizer [3] have been proposed as signal processing methods. If possible, the authors should compare the proposed method with these methods.

[1] https://www.doi.org/10.1364/AO.38.004387

[2] https://www.doi.org/10.1364/AO.45.002731

[3] https://www.doi.org/10.1143/JJAP.45.1079

 

Minor concerns

1. The symbol for transposition in Eq. (10) is different from the others.
2. E in Eq. (15) should be in bold.
3. The Lagrange function (17) is missing λ.
4. The same symbol v is used in Eqs. (24) and (29), but it would be better to use a different symbol to avoid confusion.

Author Response

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Reviewer 2 Report

Journal: Applied Sciences

Manuscript ID: applsci-1539797

Type of manuscript: Article

TITLE: “Two-Dimensional Interference Estimator with Parallel Structure for Holographic Data Storage Channel”

Authors: Thien An Nguyen; and Jaejin Lee

 

Dear Editor,

This work focuses on a 2D interference estimator to a parallel structure of an exploit the horizontal and vertical interference.

The presentation and exhibition of work are well commented on in the text and the bibliography describes well the background on the subject matter and the contributions of the research group.  However, the emphasis on novelty of this work is required.

This work fulfils, in my opinion, the requirements for publication in Applied Sciences.

Best regards,

Reviewer

Author Response

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Reviewer 3 Report

This article describes the effect of 2D interference estimator for holographic data storage (HDS) channel which might be useful for actual HDS system.

Similar analysis of PRML using SOVA with 2D equalizer was discussed in Ref[16], and the new points of this article may be the introduction of LRI and ULI estimators before 1D SOVA. However, the effects of proposed method are only discussed against BER in Figs. 3 through 5. In these results, the results proposed in this article look best, but there is no information about the white ratio and modulation method of original data which affect the degree of ISI. Therefore, I think it should be discussed in more detail about how did this method affect the intermediate results to improve BER and what kind of effect is expected to have on the read out of reconstructed images of the actual hologram data storage although this method was performed on the simulation.

In addition,  in equation (37) is not defined in this article. Please define it.

Author Response

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Author Response File: Author Response.docx

Round 2

Reviewer 3 Report

You changed the linear fill factor in figure 3, so you should describe it at line 107 in page 6. 

Author Response

Thank you for your comments. We edited and described the linear fill factor at line 107 page 6.

The modified sentence in the paper:

On page 6, line 107: we changed “In this study, α = 1” into “We investigate the influence of α in Section 5”.