Centroid Error Analysis of Beacon Tracking under Atmospheric Turbulence for Optical Communication Links

Round 1

Reviewer 1 Report

It is an interesting paper and it is true that less attention is paid to the atmospheric effects on the beacon in optical communications when the beacon is a separate beam from the optical communications beam. A few comments and questions:

1. 1. Please provide a simple block diagram of the beacon system the authors are using as the baseline of the paper. I agree that they have covered the general points of what most beacon-PAT systems would consist of, but it would be helpful to see a block diagram connecting their pieces together.
   2. Please describe the difference between the scintillation index formula in the authors equation 12 and the one in the authors reference 30, equation 7. Is this due to the spherical wave assumption?
   3. The authors simulations go to 10 sec acquisition time. That should be sufficient for a well-designed gimballed system where the optical communications system is either the sole driver for pointing or has the highest priority for pointing. But for body-mounted, non-gimballed systems, or a spacecraft juggling multiple pointing requirements, 10 seconds maybe too optimistic. What would the simulations results look like if extended to 100 seconds?
   4. What is the assumption for the size of the uplink aperture on the ground? Also, please explain the choice of a single 10W beacon from the ground for a non-communications link to a satellite at 500km altitude and a slant range of 1193km.

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

Although the focus of the article is a bit out of my specialization, the article is very interesting and deals with the innovative issue of optical data transmission.

I read the whole article carefully. The introduction seems sufficient to me, the description of the method very erudite, the results clearly presented and the conclusions based on the results - I just suggested a small extension. I went through all the equations, citations and the text and I have only one comment that I mentioned. 

I have few comments on the article:
line 269: gamma with lower index thCMOS because it is threshold.
I suggest to slightly expand the conclusion, especially to add more numerical results depending on the strength of atmospheric tubulence.

Author Response

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Author Response File: Author Response.docx

Reviewer 3 Report

The topic of the paper is very actual. I have these comments:

 - Why did you choose the diameter of the RX aperture to only 2,5 cm?

 - Some of the references are not very actual. It is possible to replace it with more recent ones?

 - There should be space between value and unit.

Author Response

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Author Response File: Author Response.docx

Reviewer 4 Report

Beacon tracking channels under atmospheric turbulence is an important research problem for optical satellite communication. However, the paper is based on just the analysis of existing work and no new contribution has been made. Therefore, I recommend rejecting this paper. 

Author Response

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Author Response File: Author Response.docx

Round 2

Reviewer 4 Report

The comments by the reviewer were not addressed at all. I again recommend reject.