Virtual Antenna Arrays with Frequency Diversity for Radar Systems in Fifth-Generation Flying Ad Hoc Networks

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This paper proposes the design of virtual antenna arrays with frequency diversity for a radar system in fifth-generation flying Ad-hoc networks. The main contribution relies on performing a Particle Swarm Optimization for a number of frequency offsets as well as the position of each array element.

Almost half of the references are conference communications. There is nothing wrong with referencing conference works, but this may be an excessive number for a journal paper. It would be interesting to substitute some of them with higher impact publications.

There may be a typo at line 86: ∆fn= (fn-fn-1)

The methodology of PSO is taken from [34]. The use of this optimization algorithm is probably the core of the manuscript, yet there is not any sort of discussion either in the introduction or in section 3 regarding the context in which PSO is used to optimize antenna arrays with respect to other state of the art approaches.
 
 The optimization aims to reduce the side lobe levels, but it could be good to discuss other aspects such as the directivity (or gain) for the computed results, since it is possible that the directivity is degraded even when having smaller SLL.
 
The authors include tables 2 and 3 as a comparison with previous studies in the field of virtual antenna arrays, but it seems to me that it is rather a review of related results included in other works, and they do not really include meaningful data that allows to determine the quality of the results obtained with the presented approach.

Comments on the Quality of English Language

Even though the writing of this paper is in general acceptable, the document would benefit from a review of the English expression in general. There are expressions such as "The c is the speed of light" that could be improved with small effort.

Author Response

Reviewer 1

This paper proposes the design of virtual antenna arrays with frequency diversity for a radar system in fifth-generation flying Ad-hoc networks. The main contribution relies on performing a Particle Swarm Optimization for a number of frequency offsets as well as the position of each array element.

Thanks for your comment.

Almost half of the references are conference communications. There is nothing wrong with referencing conference works, but this may be an excessive number for a journal paper. It would be interesting to substitute some of them with higher impact publications.

Thanks for your comment. We have added new references of journal papers, please revise the new version of the paper.

There may be a typo at line 86: ∆fn= (fn-fn-1)

Thanks for your comment. We have corrected this mistake.

The methodology of PSO is taken from [34]. The use of this optimization algorithm is probably the core of the manuscript, yet there is not any sort of discussion either in the introduction or in section 3 regarding the context in which PSO is used to optimize antenna arrays with respect to other state of the art approaches.

Thanks for your comment. We apologize for the misunderstanding, the PSO was used as a tool to find out the frequency offset and the position of each element in a Virtual Antenna Array. The main novelty of this research is the use of frequency diversity technique in virtual arrays. That’s why we did not include a deep discussion of PSO. The selection of the best optimization algorithm for this work is an open problem. We include this explanation at the end of section 3, please revise the new version of the paper.
 
 The optimization aims to reduce the side lobe levels, but it could be good to discuss other aspects such as the directivity (or gain) for the computed results, since it is possible that the directivity is degraded even when having smaller SLL.

Thanks for your comment. The directivity was added to Table 1.
 
The authors include tables 2 and 3 as a comparison with previous studies in the field of virtual antenna arrays, but it seems to me that it is rather a review of related results included in other works, and they do not really include meaningful data that allows to determine the quality of the results obtained with the presented approach.

Thanks for your comment. We presented the Table 2 as a comparison with similar works of virtual arrays, in this Table, we compare the arrays in terms of type of antenna, topology of array, frequency of operation, type of drone, and algorithm. These characteristics are very important to mature the topic. For instance, in previous works, it was using isotropic antennas with no drone structure. Now, the topic is advancing, this research used elliptic patch antennas with a quadcopter drone excited with frequency diversity. The inclusion of a real antenna and drone with frequency diversity is an advance in the topic of virtual arrays. Otherwise, Table 3 compares the design with previous FDA not with virtual arrays. This comparison was mainly based on the idea that the previous works of FDA uses hamming and logarithmic distributions, but however, this works proposes random distribution of the frequency offsets in FDVA. Please revise the new version of the paper.

Comments on the Quality of English Language

Even though the writing of this paper is in general acceptable, the document would benefit from a review of the English expression in general. There are expressions such as "The c is the speed of light" that could be improved with small effort.

Thanks for your comment. We change the expression as: “The constant c is the velocity of light in vacuum”.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Please see the attached comments.

Comments for author File: Comments.pdf

Author Response

Reviewer 2

 

This paper proposed the design of virtual antenna arrays with frequency diversity for a Radar system in fifth-generation flying Ad-hoc networks, where the virtual arrays permit to detect targets from the sky with flying drones. Generally, the authors seem have done a solid work. However, some parts need to be further clarified. The reviewer has the following concerns:

1. It is suggested to add some brief introductions of the backgrounds and facing challenges at the beginning of the abstract to make it more clear.

Thanks for your comment. We have added brief introductions of the backgrounds at the introduction section. Please revise the new version of the paper.

2. Both the motivations and contributions should be further improved. The authors need to clarify why they investigated this paper, and introduce the difference compared to the similar existing works. Besides, the novelty also should be clarified.

Thanks for your comment. We have added the motivations and contributions to the new version of the paper.

3. It is suggested to introduce the following recent work in UAV [R1], communication optimization [R2]-[R3] and 5G [R4] fields to highlight the state-of-art of this paper: [R1] “Supporting IoT with rate-splitting multiple access in satellite and aerial-integrated networks,” IEEE Internet of Things Journal, vol. 8, no. 14, pp. 11123-11134, Jul. 2021. [R1] “Refracting RIS aided hybrid satellite-terrestrial relay networks: Joint beamforming design and optimization,” IEEE Transactions on Aerospace and Electronic Systems, vol. 58, no. 4, pp. 3717-3724, Aug. 2022. [R3] “Robust design for intelligent reflecting surface-assisted secrecy SWIPT network,” IEEE Transactions on Wireless Communications, vol. 21, no. 6, pp. 4133-4149, Jun. 2022. [R4] “Covert mmWave communications with finite blocklength against spatially random wardens,” IEEE Internet of Things Journal, vol. 11, no. 2, pp. 3402-3416, Jan. 2024.

Thanks for your comment. We have added the recommended articles to our list of references.

4. The figure 1 is quite confusing. As the antenna is located on the side of the drone to focus the radiation on the front, what is the meaning of labeling 131mm between two wings of the UAV?

Thanks for your comment. The meaning of labeling 131 mm=1.52 λ is to show the size of the drone model because during the optimization the drones cannot be close to each other. That’s why we defined a search space of spacing from 1.7 λ to 2.7 λ. As the minimum spacing among the drones is 1.7 λ less than 1.52 λ, the drones are avoided to be overlapped. This explanation was added to the revised version of the paper.

5. The authors claimed that the proposed PSO algorithm “obtaining optimum radiation patterns”, the optimality should be proved and explained. 6. The comparisons to other works in simulations are limited and need to be improved.

Thanks for your comment. We have added two Figures of the fitness function versus the number of iterations for the case of N=9 and N=12 antennas with no symmetry. In this Figure, we can observe the performance of PSO, it converges at the optimum solution. Please revise the version of the paper.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

Alberto Reyna et al. reported a new design of virtual antenna arrays with frequency diversity for a Radar system in 5G flying Ad-hoc networks. The performance of virtual arrays with random frequency offsets and inhomogeneous node positions is investigated to find the optimal conditions. Several comments to address are provided below.

1. This manuscript proposes a virtual antenna that operates at 3.5 GHz, and the authors should add motivation and a rich background on why they chose the 3.5 GHz band in the Introduction.

2. The Antenna element proposed by the authors is very similar to that in reference [33], and the differences and improvements from that article need to be explained. And why such type of antenna unit is chosen.

3. The authors provide a lot of comparisons of previous work in Tables II and III, but they do not represent the improvement of this paper's work on VAA performance well, and the authors should have added more discussion instead of just listing the results.

Author Response

Reviewer 3

Alberto Reyna et al. reported a new design of virtual antenna arrays with frequency diversity for a Radar system in 5G flying Ad-hoc networks. The performance of virtual arrays with random frequency offsets and inhomogeneous node positions is investigated to find the optimal conditions. Several comments to address are provided below.

1. This manuscript proposes a virtual antenna that operates at 3.5 GHz, and the authors should add motivation and a rich background on why they chose the 3.5 GHz band in the Introduction.

Thanks for your comment. The main motivation to use the 3.5 GHz is because this band was recently opened for 5G systems. In this case, the new FANET’s will require to be communicated with new 5G systems soon. The current FANET’s uses the traditional band of 2.5 GHz and 5.5 GHz.

This explanation was added in the introduction section.

2. The Antenna element proposed by the authors is very similar to that in reference [33], and the differences and improvements from that article need to be explained. And why such type of antenna unit is chosen.

Thanks for your comment. The antenna element was taken from the literature and was tuned to be working at 3.5 GHz with other material. We selected this element because it is low profile, which is an important characteristic when the antenna is mounted in a drone. Nevertheless, the drone can use a different antenna element. The selection of the best antenna for a frequency diversity virtual array is an open research topic. The paper is only focused on the use of frequency diversity technique in virtual arrays. This explanation was added to the revised version of the paper.

3. The authors provide a lot of comparisons of previous work in Tables II and III, but they do not represent the improvement of this paper's work on VAA performance well, and the authors should have added more discussion instead of just listing the results.

Thanks for your comment. The next detailed discussion was added to the revised version of the paper:

 “Moreover, most previous works use isotropic and dipoles antennas with no drone structures. However, the scenario of real antennas mounted on a drone is very important before a real experimentation. Other works utilizes patch antennas at a frequency of 2.4 GHz. Here, the designs utilized the recently opened band of 3.5 GHz. Otherwise, the previous papers designed virtual arrays with other techniques such as time modulation or only random positions. So far, it was not used the frequency diversity in virtual arrays. This is an advance in this topic which permits the topic to mature.”

“In this case, Table 3 compares the most representative works in this field. Most of these works present the FDA with linear topologies and isotropic antennas. The frequency offsets are hamming, logarithmic, and random distributions. The main difference concerning this work is the combination of random frequency offsets and non-uniform antenna locations, the 5G frequency band, and the use of elliptic patch antennas mounted on real drones.”

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

I think that the review changes have improved the quality of the manuscript.

Reviewer 2 Report

Comments and Suggestions for Authors

The authors have well addressed all my concerns, no further comments.

Reviewer 3 Report

Comments and Suggestions for Authors

The author answered my question and the manuscript can be published in its present form.