Energy Efficiency of Unmanned Aerial Vehicle with Reconfigurable Intelligent Surfaces: A Comparative Study
Round 1
Reviewer 1 Report
The contribution of the paper lies in investigating the performance of a UAV-RIS-enabled network with passive and/or active reflecting elements in terms of the energy efficiency. The paper is generally readable. However, the organization can be improved and there are some grammatical and syntax mistakes. Hence, this paper cannot be accepted in its current form. The authors are suggested to modify this paper according to the following comments:
1) The title of the paper is confusing. Thus, the authors should change the title of this paper to reflect its actual content.
2) As there are numerous papers that investigate UAV-RIS networks, the authors should more clearly highlight the main contributions of this paper to ascertain the main technical contributions and improvements of this paper compared with previous work. Thus, the authors may provide a table summarizing the main differences/similarities of their paper with respect to the state-of-the-art.
3) This manuscript involves many emerging techniques, e.g., UAV, relays, RIS. Please further illustrate the advantages of those combinations in Section 1. In short, the motivation for using these technologies together is not clear.
4) A discussion on the practical use case scenarios of the considered network will be useful.
5) The authors adopted the Rician fading channel model. Please describe the reason of this channel modeling and how the strength of the line-of-sight component affects the performance.
6) Fig. 4 studies the energy efficiency in terms of the number of antennas. Please describe the reason of this configuration and justify whether the channels are uncorrelated. In general an adequate distance between antenna elements is required for uncorrelated channels, which may be not feasible in size-constrained UAVs.
7) A "Definition of Parameters" table would be helpful in this paper to improve reader understanding.
Author Response
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Author Response File: 
Author Response.pdf
Reviewer 2 Report
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Comments for author File: Comments.pdf
Author Response
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Author Response File: Author Response.pdf
Reviewer 3 Report
The purpose of this paper is to compare the energy efficiency of active, hybrid, and passive RIS-UAVs to that of conventional UAV relays. The authors should address the following points during the revision:
In the Introduction section, the authors should compare full-angle reflection by UAV-assisted RIS to half-space reflection and multiple reflections by conventional terrestrial RIS.
At the end of the Introduction section, research gaps and major contributions should be highlighted.
In section 3, the simulation parameters can be presented in tabular form.
Authors should justify the choice of simulation parameters.
In RIS, the number of reflecting elements is assumed to be 256. What happens if we raise this number to 512 or higher?
How do you validate the pattern of curves in Figures 2 to 6? Authors should compare theoretical results with extensive Monte-Carlo simulations.
The percentage improvements in energy efficiency should be highlighted in abstract and conclusions.
Author Response
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Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Τhe authors have addressed my major concerns in a reasonable manner. The paper has been significantly improved and the revised version can be accepted for publication.
