Review Reports

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Comments 1: General Evaluation

       The manuscript clearly falls within the scope of Sensors, as it addresses topics relevant to the journal's thematic focus, such as the optimization of demodulation algorithms for eLoran receivers, which has important application value and is in line with the journal's preference for research that combines practicality and innovation.

In this manuscript, the author's research focuses on the demodulation challenges of eLoran systems in complex environments, and innovatively proposes two algorithms, MC-NF and PMC-NF. The former effectively suppresses noise and in band continuous wave interference through notch filtering, while the latter achieves a performance improvement of about 2.8 dB by combining modulation modes. The experimental design is comprehensive and the verification is sufficient, providing a highly robust demodulation scheme for eLoran systems, which has important practical value for improving PNT backup systems.

Comments 2: Title, Abstract, and Keywords

The title and abstract of the manuscript accurately reflect its content. The keywords are appropriate and relevant.

Comments 3: Manuscript Structure and Section-Specific Comments

3.1 Section 2.1.1

Section 2.1.1 does not explain the specific physical meanings of the three states ("-", "0", "+") in "three state pulse position modulation (PPM)" (such as the offset of the pulse relative to the reference position).

It is suggested to add "-" to indicate that the pulse lags behind the reference position by 1 μ s, "0" to indicate no offset, and "+" to indicate that it leads the reference position by 1 μ s "to help readers understand the modulation mechanism.

3.2 Section 3.2.3

The reason for the statement 'better demodulation performance when the interference frequency is far away from the eLoran center frequency' in section 3.2.3 is not explained. It is suggested to add 'notch filters attenuate interference signals further away from the 100kHz center frequency, so the larger the deviation between the interference frequency and the center frequency, the better the interference suppression effect and demodulation performance'.

3.3 Structure

The numbering structure of the manuscript needs some adjustments, with numbering 1. 2. 3. ...... The label level here should be lower than the number 2.2.4.

Comments 4: Comments on the Equations

4.1 Equation (3) and (4)

In the Section 2.1.3 "Evaluation of Demodulation Performance", Equations (3) and (4) correspond to the calculations of Group Demodulation Accuracy Rate (GDAR) and Frame Demodulation Accuracy Rate (FDAR), respectively, which are core indicators for quantifying the demodulation reliability of the eLoran system at different granularities.

It is recommended to supplement the definitions of key parameters: clarify that P_group refers to the number of correctly demodulated pulse groups, and P_frame denotes the number of correctly demodulated data frames after RS encoding and CRC verification, so as to ensure the equations are clear and understandable.

4.2 Equation (18)

In the Section 3 "Notch Filtering design", Equation (18) correspond to the definition of α is "α=sin (ω0)/(2Q)", but the physical meaning and value basis of Q (quality factor) are not explained. Only Q=5 is mentioned in the experimental design.

It is recommended to add the meaning of Q in the formula definition (such as characterizing the frequency selection characteristics of the notch filter, the larger the Q value, the narrower the notch bandwidth), and explain why Q=5 is chosen (such as matching the 20kHz bandwidth requirement of eLoran signal).

Comments 5: Comments on Tables and Figures

In figure 8, it appears in low resolution. Besides, any figures should not extend beyond the page margins. It is suggested that the full text should be formatted according to the requirements of the journal.

Comments 6: Bibliography

Some bibliographies are not standardized in format, such as [7] , [33] and [40]. These bibliographies does not include DOI numbers for publications.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

This manuscript investigates robust demodulation techniques for enhanced Loran (eLoran) systems operating in complex interference environments. The authors propose two signal processing algorithms—Matched Correlation integrating Notch Filtering (MC-NF) and its pattern-based extension (PMC-NF)—aimed at improving demodulation accuracy under random noise, skywave interference, and in-band continuous wave interference (CWI).  The manuscript is well written and technically solid, and the proposed methods demonstrate clear benefits for eLoran demodulation. The following comments are intended to help further strengthen the paper.

1) While the proposed MC-NF and PMC-NF algorithms show clear performance gains, the core techniques (matched correlation and notch filtering) are well established. The novelty primarily lies in their integration with eLoran modulation patterns and pulse-group processing. The authors should more explicitly emphasize the system-aware nature of the contribution, particularly the pattern-level demodulation and its impact on GDAR/FDAR, and clarify how PMC-NF differs conceptually and practically from existing correlation-based or spectrum-based demodulation approaches.

2) The manuscript mainly compares MC-NF and PMC-NF with the traditional MC algorithm. While the present is a reasonable baseline, readers would benefit from a clearer comparison with recent methods such as EC-PD, PSSD, or machine-learning-based demodulators. The reviewer suggests that a concise comparison table (qualitative or semi-quantitative) should be included for summarizing performance, robustness, computational complexity, and implementation feasibility.

3) The criterion used to detect in-band CWI (normalized FFT amplitude difference > 0.15) appears empirically selected.  Thus, to demonstrate robustness against threshold variation, the justification for this threshold or a short sensitivity analysis should be provided.

4) The study relies entirely on simulation results. Although extensive, the absence of real measurement data limits practical validation.  I think the discussion about expected real-world performance and hardware implementation considerations must be expanded. Moreover, for future work, the field testing and receiver-level validation should be clearly identified.

5) Please ensure consistent use of terms such as “matching correction” and “matched correlation” throughout the manuscript.

6) Some figures would benefit from clearer legends and larger font sizes to improve readability, particularly for PDAR and GDAR curves.

7) A brief comparison of the computational cost of MC, MC-NF, and PMC-NF would help readers assess real-time feasibility.

 

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

Reviewer Comments

The authors have proposed a new matched correlation demodulation method with notch processing. Moreover, the matched correlation integrate notch demodulation method is further modified to improve demodulation performance. The study seems to contribute to conventional research. However, there are several technical and presentation-related issues that must be addressed before this work can be considered for publication.

 

 

Technical Concerns

1. My main concern is that the authors have not compared their proposed method with any recent and relevant studies. Apart from the comparison between PMC-NF and MC-NF, no other existing state-of-the-art methods have been evaluated on the considered benchmarks.
2. The proposed method should be presented in the form of an algorithm or flowchart for better clarity and understanding. In its current form, the methodology is not fully understandable.
3. In Figures 16–17, the PDAR values of the MC method appear to be completely inconsistent with expectations. These results should be carefully verified. If they are indeed correct, then the authors should consider comparing their method with another recent technique that demonstrates reasonable performance on the adopted performance scale.
4. It is surprising to observe that the MC method achieves GDAR values very close to those of the proposed method, while its PDAR values degrade drastically in comparison. This contrast needs further explanation.
5. The authors have not provided the parameters used for generating the random noise, which is a crucial component of the study. These details must be clearly stated.
6. The number of Monte Carlo simulations used to generate the experimental results has not been mentioned. This information is essential and should be included.
7. The “Discussion” section is very brief and lacks depth. It requires significant improvement with more detailed analysis and interpretation of the results.
8. Most of the references are outdated. Out of 40 references, only three are from 2024, while the majority are considerably old. More recent and relevant literature should be incorporated.
9. The “Data Availability Statement” should be carefully reviewed and revised if necessary.

 

Clarity and Readability

1. Figures
   • In some Figures, the text is overwritten on the plot. For e.g., in figure 8.

 

 

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

Comments and Suggestions for Authors

The authors have responded to all comment. Just a minor comment

The authors can recheck figure 3a and 3c where legend is overwritten on plots.

Author Response

General Response: We sincerely thank the reviewer for taking the time to review our revised manuscript and for acknowledging our efforts in the previous round of revisions. We appreciate your careful attention to detail, which has helped us ensure the highest quality of presentation. Please find our response to the specific comment below.

Comment: The authors can recheck figure 3a and 3c where legend is overwritten on plots.

Response: Thank you for this helpful reminder. We apologize for the oversight in the previous version. We have adjusted the layouts of Figure 3a and 3c to ensure that the legends do not overlap with the plot curves. The updated figures have been included in the revised manuscript.