Investigation of Characteristics of Ultraviolet Light Pulse Weak Signal Communication System Based on Fourth-Order Frequency-Shift Keying Modulation

Round 1

Reviewer 1 Report

The authors demonstrate theoretically and experimentally a UV weak light pulse communication by using the 4FSK Modulation technique. Their technique utilizes an optical pulse processing algorithm, which can enhance the demodulation sensitivity on the photon level. Their system shows an improved performance as well. The study addresses an interesting solution that can help in UV communication technology. The conclusions together with the presented results are consistent with the manuscript's arguments. In addition, the manuscript is well-written. 

I have the following comments for the authors, which may further improve the manuscript quality:

·        The authors should provide a block diagram of the entire system.

·        The study misses the effect of electronic noise (especially of Op-Amp) on photon counting errors. The authors should comment on that and provide some data estimating such noise.  

·        On Page 7, first paragraph, the voltage threshold is optimized considering multiple factors. The authors should elaborate on this optimization, showing their optimization method and some optimization curves.

·        A comparison between the simulation and experimental results should be provided, and explain the source of deviations or errors, if any.

·        The authors have focused on a single scattering model. What about the effect of multiple scattering? Could the authors comment on that and provide their expectations?  

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

This article has presented an investigation on the use of 4FSK modulation scheme for UV light pulse weak signal communication system. The major limitations of the article are listed as:

1.      The abstract does not provide (1) the motivation behind the target research problem. Why are the authors using a 4FSK modulation scheme instead of OOK? (2) the limitation(s) or shortcoming(s) of existing approaches (research gap) (3) the main feature of the proposed approach that will address the shortcoming(s) of existing solutions (4) what is the significance of achieved outcomes in terms of certain performance attributes

2.      The problem statement in the Introduction is not clearly articulated. The challenges associated with the existing systems, particularly related to OOK, must be described.

3.      The research gap in the Introduction (summary of the state of the art as well as their limitations) is not presented. The description of “what has been achieved so far” for the improvement of UV communication and “what are the major shortcomings of existing solutions” has not been presented. The second and third para of Introduction briefly present some of the work done in this area which is not sufficient. Have other researchers used 4FSK for the target problem? If no, then what is the reason.  

4.      A background section is also missing where authors may provide the essential knowledge to understand the working of a typical UV communication system. This section may include a block diagram of a UV communication system and terminologies specific to a UV communication system could be explained.

5.      Related work has not been analyzed properly to establish the novelty of this work. For example, what modulation schemes other than OOK are used in a UV communication system? What are their advantages and disadvantages, etc.? Why the authors chose 4FSK rather than binary FSK? The justification of using 4FSK has not been clearly established.

6.      The justification for using a discrete Poisson channel distribution has not been clearly mentioned.

7.      To describe the data rate, authors have used three terms: symbol rate, transmission rate and communication rate. However, the unit of all the rates has been shown as “bps” except for line 182 on page 6 where the unit of symbol rate (R) has been shown as Hz. What is the difference between these rates? How come they have the same unit (bps)? This should be clarified. Line 274 on page 8 mentions the symbol rate as 2.5 kbps while the overall transmission rate is mentioned as 5 kbps. Probably, by symbol rate, authors refer to the 2-bit symbol in a 4FSK scheme. In that case, the unit of symbol rate should be 2.5 kilo symbols per second. If this is the case, then the units of symbol rate must be different than the overall transmission rate (called “bit rate” in the communication world). This must be fixed throughout the paper – in the text as well as in the figures.

8.      Section 3.2 gives a formula for calculating the “width” (W) of each symbol. What do the authors mean by “width”? Do they mean number of bits? This should be clarified.

9.      For a 4FSK modulation scheme, since one symbol carries two bits, the symbol rate (R) and overall transmission rate (say, B) are related by, B = 2 x R and this relation is well known and does not change. Then what is the significance of Figure 4?

10.  Line 92 on page 3 mentions, “The path loss, designated as L, is defined by the researcher as the …”. What do the authors mean by “researcher”? Which researcher are they referring to?

11.  The heading of Section 2 is, “Analysis of Scattering Models and Channel Characteristics”. Under this section, there is a subsection “Communication System Block Diagram” in which the authors have described their proposed system. This subsection is a misfit Section 2. There should be an exclusive section on the proposed model (or system) where the authors should present their proposed work.

12.  With reference to the simulation results, how many bits did the authors transmit to generate Figure 7(b)?

13.  There is no performance comparison with recent work and/or the work done by others which is critical to establish the novelty of the presented work.

The limitations of the proposed work such as the complexity, implementation issues, 

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

1- The article briefly notes a tiny difference between the ultraviolet light source wavelength and the peak wavelength of the optical filter, but there is no in-depth examination. A more detailed examination of this deviation's impact on system performance will improve the study.

2- The research discusses the impact of environmental noise on system performance, but it does not go into detail about other environmental variables such as air conditions and interference from neighboring light sources. A thorough examination of these variables would improve our understanding of the system's real-world performance.

3-The research presents experimental results for NLOS and LOS communication situations but does not conduct a comparison analysis between them. A detailed comparison of performance parameters such as BER trends, transmission distance, and system stability in NLOS and LOS scenarios would provide more clarity and insights.

4- The paper offers BER values for several experimental configurations, however it does not go into detail about error sources and their implications for system reliability. An in-depth error analysis, along with explanations of probable error sources and mitigation measures, would strengthen the paper's credibility and provide significant insights for future research.

5- The article briefly addresses potential research fields, however it lacks a full description of particular improvements to the UV weak light communication system. Providing specific advice would strengthen its contribution to the field.

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Authors have addressed all the comments. The paper can be accepted.

Reviewer 3 Report

The authors addressed all the required comments.