Experimental Study on FM-CSK Communication System for WSN

Round 1

Reviewer 1 Report

Some points:

1) The authors mention that they carry out a study of chaotic communication systems based on frequency modulation (FM-CSK) that has application in WSN. They evaluate three types of chaotic oscillators that are used in the study and find that there can be a tolerance of +- 10% in the variation of the nominal values of the electronic elements without affecting the synchronization, which is crucial in this type of communications. They also mention that they test experimentally with an AWGN channel, obtaining BER curves of the three systems studied.

2) It is clear to me that the main contribution of the authors is described in lines 68 – 76 in the introduction section, and that it is based on an improvement of their previous proposal that the same authors have presented in reference [12], in 2020. Among the problems they solve is the periodicity of the chaotic signal. In the present work the previous one is improved, using two chaotic signals, but reducing an oscillator in reception, since it uses the substitution method for synchronization, and apparently simpler analog circuits are used as oscillators.

3) It's not clear to me how low cost would be an advantage for WSN applications; It is clear to me that the implementation of this communication system, although a very good proposal to provide communication security at the physical layer level, would add greater complexity in transmission and reception and, therefore, greater energy consumption.

In addition, apparently, in principle, more bandwidth is required, since two signals would be needed to carry out the transmission, one of which would not carry any information, although it would only support synchronization, in both it is necessary to carry out everything the process of modulation, filtering, etc. They mention that they can transmit in parallel using different frequencies or different polarization, although I think that would also add more complexity to the system.

I do agree that, in this type of communication, adding FM-CSK helps improve transmission security, but I would not dare to say that it is low cost or low energy consumption, which would be the main feature that the authors mention that it has and that it would justify its potential application in WSNs. I am not opposed to studying and applying it, that is very good, it is a very good idea; only that I would not dare to affirm that energetically it has advantages, it would be necessary to detail more if the authors have found any study where such affirmations have been demonstrated, I believe.

4) On the other hand, I do not see where the approach for communication systems with application for WSN that the authors have mentioned in the abstract, introduction and conclusions is explained or detailed. Until now I don't see any difference with respect to any communication system where chaotic communications is applied to improve security. I think it is necessary to give more solidity to the arguments that justify the approach to WSN, because what has been explained in the article, in my opinion, although very well explained, has a generic approach to communication systems. If a better argument is reached, they could even add six more letters at the end to the title: “…. for WSN”.

5) In lines 211-215 they mention that they carry out a verification with a theoretical approach, in line 449 they mention that there is a theoretical analysis and in line 250 they mention that they have done a theoretical study.

But I only see, from section 3, a very good summary of the main types of chaotic oscillators and their differential equations. In the same section I see the equation for the correlation coefficient, which helps determine if the received bit is 1 or 0, but I do not see any study to be analyzed. A study and analysis imply that there was some process in which analytical results have been obtained that can be discussed; all the results that have been put in the tables refer to simulation and hardware implementation results. Experimental results (BER, Frequency Spectrum) are shown in the graphs.

6) In lines 211-215 they mention that they use an electronic model development. On line 252 they mention prototypes of selected chaos oscillators.

Where are those prototypes? At least I miss the implemented circuits, the three circuits that they mention (Chua, Vilnius, RC). Where are the circuits or hardware they mention? Was it a pre-made card for testing? Figure 6 shows an image of a card, I don't know if it's real, do you use a pre-made card that can be configured? Didn't the authors build their own circuits? Does that have to do with the fact that there have been hardware restrictions in the experiment and that the authors mention in lines 319-320?

7) I see the reference dates old, the newest dates from 2020 (a couple), one of them being a self-citation that they take as a basis and improve in this work. I think that in reference 13 the information is not complete.

Branislav Jovic, “Chaotic Signals and Their Use in Secure Communications,” 2011

Jovic, B. (2011). Chaotic Signals and Their Use in Secure Communications. In Synchronization Techniques for Chaotic Communication Systems (pp. 31-47). Springer, Berlin, Heidelberg.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

This study presents a low cost approach to chaos oscillators for FM-CSK. But there are some relevant aspects that should be addressed.

The references don't link to bibliography. Figure references doesn't link to figure.

Introduction should be reorganized and improved.

Section 2 should be Materials and methods. The manuscript does not follow standard organization.

Figure 1. Bottom of figure is cropped. Arrows to decoding block are no straight

Figure 7. Improve this figure, consider using 4 individually subfigures

Figure 8. Idem.

Table 1. Please clarify in the caption that the values are correlation coefficients.

Table 2. Idem

Figure 11. Please clarify near bandpass filter its acronym (BDF) used in the figure legend

Figure 13. The quality of the image can be improved

Electronic components like capacitors, resistors, inductances, transistors... are subject to tolerances. How the chaos oscillator performs considering the uncertainty/tolerances of the components? Reactive component has been studied but not the other components. Could you provide some experimental results?

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

The whole article is relatively smooth and has certain practical significance, but there are also some problems as follows: 

The abstract of this paper needs to be modified to include not only the experimental background, methods and experimental results, but also a simple comparison with previous methods and the advantages of the author's own method.

The author's introduction needs to be optimized, and we suggest that the author evaluate what needs to be improved in the introduction according to the following criteria.

a. What is the problem to be solved?

b. Are there any existing solutions?

c. Which is the best?

d. What is the main limitation of the best and existing approaches?

e. What do you hope to change or propose to make it better?

f. How is the paper structured？

When the authors cite references, most of them are simply displayed in the paper. We suggest that the authors relate these references to the work of this paper, for example, how certain studies have influenced their work.

Please clearly highlight how your work advances the field from the present state of knowledge and you should provide a clear justification for your work. The impact or advancement of the work can also appear in the conclusion.

The most important aspect which I see the authors have left out is a comparison of results. The authors should benchmark their work with existing state of the art.

The authors need to reconstruct most of their sentences and observe their use of tense.

The conclusion of this paper needs to be optimized. We suggest that the author add some comparisons with previous work, advantages and disadvantages of the author's method, and prospects for future research directions.

Author Response

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Author Response File: Author Response.pdf

Reviewer 4 Report

This study of the FM-CSK communication system looks interesting and technically correct. Here are some detailed comments for further improving this work.

• The authors say ”… the environment becomes smarter, safer, and more automated,”. I agree that the environment becomes smarter and more automated, but I am not sure whether it becomes safer. The authors might want to be more rigorous about the words that they choose.
• In figure 12, it seems that the red curve has a trend of going up at the end, but the other two curves do not. Is there any particular reason for this phenomenon?
• For the software implementation (simulation), what are the computational complexity (time or space) of the algorithms involved?

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

The changes improved the readibility of the work

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

We are glad to see that the quality of this paper has been greatly improved and the content is more substantial after the revision.  We are grateful for the efforts of the authors and believe that the paper could be ready for publication with a few language modifications.  

Author Response

Please see the attached file.

Author Response File: Author Response.pdf