UAV Digital Twin Based Wireless Channel Modeling for 6G Green IoT

Round 1

Reviewer 1 Report

Generally speaking, authors have presented a thorough exploration of the implementation of Digital Twin (DT) technology in unmanned aerial vehicle (UAV) networks. The authors aim to make a significant contribution to the green IoT space, offering a comprehensive methodology for UAV RF representation.  First, about significance and novelty: the paper is timely and the proposed digital twin-based UAV network system for green IoT represents an innovative contribution to the field. The authors clearly articulate the need for this work in the context of the upcoming 6G technologies and environmental sustainability concerns. The unique integration of DT technology, radar imaging, and AI-driven task management in UAV networks is particularly compelling. Second, considering the clarity and organization, I suppose, the paper is generally well-written, with a clear structure and logical flow.

 

Moreover, about the technical soundness, the technical aspects presented in the paper are sound, demonstrating a solid understanding of UAVs, mmWave communication, digital twin technology, and AI. In addition, the paper adequately validates the proposed model through simulations, and the results are clearly presented and discussed. However, the inclusion of real-world scenarios or case studies would provide stronger evidence of the system's practicality and robustness.

 

Despite the general novelty and competitiveness of this paper, there are several aspects the authors can seek to improve the overall quality：

 

First, in the introduction part, the authors have written: “In order to meet the demand for broadband access at any time and any region not only for people but also for a wide variety of things, the sixth-generation mobile communication technology (6G) will build a space-air-ground integrated network (SAGIN).” Such an expression is not precise and lacks support. The best way to avoid such problems is to add literature from both academia and industry/regulations (such as 3GPP). Therefore, some references such as [1] and [2] with some proper elaborations are suggested.

 

Second, the authors have mentioned weather factors for UAVs, and 3D ray-tracing methods used for channel modeling of mmWave UAV communications and sensing, some proper review of existing literature is better given, such as [3] and [4].

 

Third, the authors have mentioned that “it is reasonable to posit that mmWave is more appropriate for UAV communications at lower altitudes than low earth orbit (LEO) satellites, which can further contribute to energy efficiency [11]-[12].” The tone of this conclusion is actually too affirmative.

Usually, it is better to avoid using such an absolute tone unless you are really sure about it. UAVs and Satellite Communications using mmWave for comm. both have pros and cons. For example. UAVs need to consume a large amount of energy on mechanical maneuvers, which means they cannot fly very far away and their battery/gasoline can be quickly drained, while LEO constellations do not have such concerns, and they can work 7-24 without energy refill, although the sats. communication distance is much larger. It really depends on the application scenarios of using UAVs and/or satellites and how to use them.  

 

Last but not least, the discussion could be expanded to provide a more detailed analysis of how the presented work compares to existing solutions. In particular, discussing how the specific choice of UAV model, the DJI Phantom 4 Pro quadcopter, influences the outcomes and how different models might perform in this framework would be beneficial.

 

[1] J. Liu, Y. Shi, Z. M. Fadlullah and N. Kato, "Space-Air-Ground Integrated Network: A Survey," in IEEE Communications Surveys & Tutorials, vol. 20, no. 4, pp. 2714-2741, Fourthquarter 2018, doi: 10.1109/COMST.2018.2841996.

 

[2] X. Lin, S. Rommer, S. Euler, E. A. Yavuz and R. S. Karlsson, "5G from Space: An Overview of 3GPP Non-Terrestrial Networks," in IEEE Communications Standards Magazine, vol. 5, no. 4, pp. 147-153, December 2021, doi: 10.1109/MCOMSTD.011.2100038.

 

[3] M. Song, Y. Huo, Z. Liang, X. Dong and T. Lu, "Air-to-Ground Large-Scale Channel Characterization by Ray Tracing," in IEEE Access, vol. 10, pp. 125930-125941, 2022, doi: 10.1109/ACCESS.2022.3224776.

 

[4] L. Bai, Z. Huang, L. Cui and X. Cheng, "A Non-Stationary Multi-UAV Cooperative Channel Model for 6G Massive MIMO mmWave Communications," in IEEE Transactions on Wireless Communications, doi: 10.1109/TWC.2023.3269203.

Some expressions need double check and reconsiderations.

Author Response

Your suggestions greatly enhanced our article. Thank you. We've detailed our responses to your comments in the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

In this work, the authors elaborate on the use of unmanned aerial vehicles in interaction with digital twins. This is to serve in applications such as the green Internet of Things. Results are provided to corroborate the proposed analysis. The paper, however, is not very well written. This reviewer's comments are listed below:

Comment 1:

Since unmanned aerial vehicles are used on demand, what challenges are related to their utilization as antennas? From their waiting point to the point of exploitation, how will this work? How do you handle delays?

 

Comment 2:

What will be the ratio of quality of service vs. price? How many drones will be used for a single target? and if the target moves?

 

Comment 3:

Will unmanned aerial vehicles have reconfigurable antennas or reconfigurable surfaces? Commenting on these will help the reader gain a broader view of the situation.

 

Comment 4:

In this reviewer's opinion, it is not clear how Digital Twin fits into the rest of the paper. My impression is that even without a Digital Twin, the authors could obtain the same results. Could you explain further?

 

Comment 5:

Please elaborate more on how Fig. 5 is obtained.

 

Comment 6:

The paper is poorly written.

a- The figures' captions and sub-captions must have a dot at the end.

It is mandatory to punctuate all equations.

c- Some figures like Figs. 8 and 10 look blurry.

d-All figures should speak. Some are very quiet, like Fig. 6.

e- Multiple Input Multiple Output---- why the capital letters?

f- The paper should be further polished.

The paper should be further polished.

Author Response

Your suggestions greatly enhanced our article. Thank you. We've detailed our responses to your comments in the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

This paper explored the integration of drones and digital twin technology in the context of 6G green Internet-of-Things. Herein are some comments to improve the quality of the article:

*The abstract needs improvements; does not reflect the content of the article well.

*The Introduction effectively introduces the paper's main concepts but could be enhanced by emphasizing the research's significance and potential advancements in the field. In addition, list the contributions and novelty of the article in the bullet points. Recommend emphasizing and highlighting the link between digital Twin and Green IoT in the introduction well. Thus, I recommend the following articles for a better understanding of the Green IoT: (i) Green IoT: A review and future research directions; (ii) Green Internet of Things (GIoT): applications, practices, awareness, and challenges; (iii) Energy harvesting techniques for wireless sensor networks/radio-frequency identification: A review.

*Section 2 should be related to works. Providing a brief overview of the current state-of-the-art in this area would also help readers understand the paper's position within the existing literature. Moreover, provide a summary Table of the literature at the end of this section with the highlight of the new of this study.

*focus on characterizing the RF characteristics of the digital twin using 3D mmWave Radar imaging. To enhance clarity, consider elaborating on the specific steps involved in this characterization process. Additionally, provide a clearer explanation of how the proposed wireless channel modeling based on ray tracing contributes to the alignment of RF domains between the DT and physical UAVs.

*Ensure that the references are up-to-date and relevant to the topics discussed in the paper. Consider incorporating recent studies that explore the integration of digital twin technology in UAV networks and the advancements in 6G green IoT.

 

Readable

Author Response

Your suggestions greatly enhanced our article. Thank you. We've detailed our responses to your comments in the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

I am satisfied with the latest revision

Readable