FANET Routing Protocol for Prioritizing Data Transmission to the Ground Station

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

To improve the quality of the paper, the reviewer gives the following comments.

(1) In Figure 3, the processes “Send data to destination using cached route”, “Cache data and wait for next GS flood”, and “Forward data to destination via satellite link” cannot come to the end.

(2) In Table 4, the meaning of “HeMcs0”, “HeMcs2”, and “HeMcs7” is unclear.

(3) The paper needs to explaining the yellow color lines in red boxes and the orange color lines in purple boxes in Figure 8.

(4) In Section 4.3.2, the meaning of “Even when the destination nodes were not limited to the GS” is unclear.

(5) Section 5.2 says “we observe that the proposed method uses fewer control IP packets than AODV, which achieves the highest PDR under 2 s among the existing protocols”. Please indicate which figure in Section 4 supports this claim.

Comments on the Quality of English Language

The paper writing should be polished. The writing errors include “These results indicate that the proposed method can achieve sufficient throughput even when compared with realistic satellite communication” in lines 300-301 and “those under which greater reliance on satellite communication is” in line 362, etc.

Author Response

Dear Reviewer,

 

Thank you for taking the time to review our work.

We have followed all the suggestions provided. We have bolded all your comments. We have also written our response below each comment.

 

1. In Figure 3, the processes “Send data to destination using cached route”, “Cache data and wait for next GS flood”, and “Forward data to destination via satellite link” cannot come to the end.

 

We revised Figure 3 to ensure that the three processes properly terminate at the end state.

 

2. In Table 4, the meaning of “HeMcs0”, “HeMcs2”, and “HeMcs7” is unclear.

 

In the revised article, the former Table 4 is now Table 6. We added the following sentences below Table 6 (around line 255) to clarify the meaning of data modes.

 

> In NS-3, 12 data modes were implemented for IEEE 802.11ax (HE), ranging from HeMcs0 to HeMcs11. The trailing number in HeMcs0, HeMcs2, and HeMcs7 corresponds to the modulation and coding scheme (MCS) index for IEEE 802.11ax (HE) in NS-3. An MCS specifies a combination of a modulation scheme and a forward error correction coding rate; a higher MCS index provides higher spectral efficiency but requires better received signal quality (e.g., higher signal-to-noise ratio).

 

3. The paper needs to explaining the yellow color lines in red boxes and the orange color lines in purple boxes in Figure 8.

 

We revised the sentence around line 300 (Section 4.3.1). Specifically, we added an explanation of what the orange line represents in each box plot.

 

> The orange line inside each box indicates the median. Focusing on the median latency, the proposed method exhibited lower latency than conventional DSR.

 

4. In Section 4.3.2, the meaning of “Even when the destination nodes were not limited to the GS” is unclear.

 

We revised the sentences around lines 346 and 356 (Section 4.3.2) to clarify the meaning of “the destination nodes were not limited to the GS.” Specifically, we explicitly stated that Experiment 2 was conducted in a scenario where the destination is not fixed to the GS and UAV-to-UAV communications are included.

 

> The proposed method outperformed existing protocols in terms of PDR under 2 s when the destination is not fixed to the GS and UAV-to-UAV communication is included, regardless of node speed, the number of mobile nodes, or the number of data streams (Figs. 16 and 17).

 

> Regardless of node speed, the number of mobile nodes, and the number of data streams, the proposed method maintained latency at a feasible level for real-world applications in scenarios where the destination is not fixed to the GS and UAV-to-UAV communications are included (Figs. 19 and 20).

 

5. Section 5.2 says “we observe that the proposed method uses fewer control IP packets than AODV, which achieves the highest PDR under 2 s among the existing protocols”. Please indicate which figure in Section 4 supports this claim.

 

We revised the sentence around line 396 (Section 5.2) to explicitly indicate the figures in Section 4 that support this claim.

 

> As shown in Figs. 10 and 12, AODV achieves the highest PDR under 2 s among the existing protocols. In addition, Fig. 14 shows that the proposed method generates fewer control IP packets than AODV.

 

6. The paper writing should be polished. The writing errors include “These results indicate that the proposed method can achieve sufficient throughput even when compared with realistic satellite communication” in lines 300-301 and “those under which greater reliance on satellite communication is” in line 362, etc.

 

We had the manuscript professionally proofread by an English editing service, and we revised various sentences throughout the paper to improve grammar, clarity, and readability. For example, we revised the sentence around line 375 (Section 4.3.4) as follows:

 

> These results indicate that the proposed method achieved sufficient throughput compared with realistic satellite uplink throughput.

 

We also revised the sentence around 441 (Section 5.4) as follows:

 

> We believe that a comprehensive evaluation considering these factors would enable a clear understanding of the conditions under which FANET-based multihop communication is advantageous and when greater dependence on satellite communication is preferable.

 

 

Thank you very much for reviewing our work

 

Best regards,

 

Kaoru Takabatake

Tokyo University of Science

Email: k.tus@pass.netsecretinbox.com

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

In this paper, the authors propose a DSR-based FANET routing protocol with a new “GS flood” option that significantly improves UAV-to-ground-station reliability and efficiency, with a particular focus on disaster scenarios. The analysis of the limitations of classical MANET protocols (DSR, AODV, OLSR) for highly mobile UAV networks and GS-oriented traffic in disaster areas is well motivated and justifies the need for a GS-prioritizing FANET protocol combined with satellite links. The experimental evaluation, which considers different traffic types (i.e., GS-only traffic and all-node traffic) as well as throughput versus Starlink uplink capacity under varying node counts, mobility speeds, and traffic loads, provides an interesting perspective.
The limitation of the work is the presence of several simplifying assumptions, which introduce practical and methodological constraints. This negatively affects the novelty of the paper, resulting in an overly simplistic contribution.

The following comments are provided:

1) There are too many simplifications in the modeling of satellite MAC behavior, interference, and regulatory constraints; moreover, UAV energy consumption, antenna weight, and terminal transmit power are deferred to “future work”.

2) Avoid the use of long dashes and replace them with commas.

3) More recent FANET-specific protocols (e.g., CHNN-DSR, BC-DSR, GCS-routing) are discussed in the related work but are not included in the experimental evaluation. At least one of these schemes should be considered for comparison.

4) The GS is assumed to repeatedly flood the network over a reliable control channel, and UAV mobility follows a Gauss–Markov model. However, the robustness of the GS flood mechanism under highly dynamic or obstructed topologies, different mobility patterns, or partial GS connectivity is not thoroughly analyzed.

5) The quality of the figures is not satisfactory, as they are too small and difficult to read.

6) The contributions should be presented more clearly, preferably using a bullet-point list, to allow the reader to easily identify the main proposals of the paper.

 

Author Response

Dear Reviewer,

 

Thank you for taking the time to review our work.

We have followed all the suggestions provided. We have bolded all your comments. We have also written our response below each comment.

 

1. There are too many simplifications in the modeling of satellite MAC behavior, interference, and regulatory constraints; moreover, UAV energy consumption, antenna weight, and terminal transmit power are deferred to “future work”.

 

We appreciate this important comment. To clarify the scope of this study and avoid overclaiming satellite realism, we added the following sentence at line 190 (Section 3) to emphasize that uplink data transmission to the GS is our primary objective, and satellite forwarding is introduced only as an auxiliary option for non-GS communications:

 

> In this study, data transmission to the GS is the primary objective, and satellite forwarding is introduced only as one possible option to enable communications with nodes other than the GS.

 

In addition, we explicitly described the simplified satellite-link model around line 222 (Section 4.1.2) and conducted additional simulations by introducing satellite packet loss rate as a parameter (0%, 1%, and 5%, with the satellite delay fixed at 0.1 s):

 

> In the proposed method, when transmitting data to nodes other than the GS becomes necessary, we utilize forwarding through the GS via a satellite downlink as a backup option. However, the appropriate downlink technology in real deployments depends on the application and environment; therefore, this study evaluated the satellite link using a simplified model, leaving comprehensive analysis for future work. Specifically, the satellite delay was set to 0.1 s, and the satellite packet loss rate was set to 0%, 1%, and 5%.

 

We reported and discussed the results around lines 350 (Section 4.3.2, Fig. 18) as follows:

 

> Fig. 18 compares the PDR under 2 s by the proposed method to Fig. 16 when the Starlink packet loss rate is set to 1% and 5%. As the Starlink packet loss rate increases, the PDR under 2 s of the proposed method decreases. However, it still achieved a higher PDR under 2 s than the other protocols.

 

We added the following discussion around line 387 (Section 5.1) to explain that, under our assumed scenario where most traffic is GS-directed, satellite forwarding is used only for a smaller fraction of traffic and thus its impact is expected to be limited:

 

> Moreover, in the scenario assumed in this study, the majority of traffic is directed toward the GS; therefore, the fraction of communications forwarded via Starlink is small. Consequently, the impact of Starlink link quality, as shown in Fig. 18, is expected to be even more limited under the assumed scenario.

 

While detailed modeling of UAV energy consumption, antenna weight, and terminal transmit power is beyond the scope of our routing-layer simulations, we added the following statement around line 403 (Section 5.2) to clarify what we can discuss within scope:

 

> Because this study focused on the routing layer, the reduction in control IP packets implies fewer transmissions, which can qualitatively reduce communication-induced energy consumption.

 

2. Avoid the use of long dashes and replace them with commas.

 

We revised the manuscript to avoid long dashes and replaced them with clearer phrasing. For example, at line 45 (Section 1), we changed “GS–UAV” to “communication between the GS and UAVs”. We also revised the sentence at line 112 (Section 2) to avoid dash-like punctuation and use comma-separated enumeration: “such as DSR, AODV, OLSR, and ZRP”.

 

3. More recent FANET-specific protocols (e.g., CHNN-DSR, BC-DSR, GCS-routing) are discussed in the related work but are not included in the experimental evaluation. At least one of these schemes should be considered for comparison.

 

We addressed it in two ways: (i) we clarified why BC-DSR and GCS-routing are not directly comparable under our target disaster-deployment assumptions, and (ii) we added a new experiment to include a CHNN-DSR for comparison.

 

First, for BC-DSR, we added the following clarification around lines 131–133 (Section 2) to explain that its assumptions differ from our disaster-area deployment and that it does not focus on efficient GS route acquisition:

 

> its assumptions differ from the scenario considered in this study, where UAVs are deployed distributively over a disaster area, and the topology changes irregularly; moreover, BC-DSR does not focus on mechanisms for efficiently acquiring routes to the GS.

 

Second, for GCS-routing, we added the following sentences around lines 140–142 (Section 2) to clarify that we do not assume an always-on control channel or centralized control by the GS, which is required by GCS-routing:

 

> However, this study accounts for distributed deployments in which certain UAVs cannot communicate directly with the GS; thus, we do not assume an always-on control channel or centralized control by the GS.

 

Finally, to satisfy the request to evaluate at least one recent FANET-specific protocol, we added Experiment 3 to compare our method with CHNN-DSR. Because the CHNN-DSR implementation is not publicly available and several parameters are not fully specified in the original paper, we reproduced the experimental environment based on the reported settings and explicitly defined the missing items to construct a consistent simulation setup. The experiment setup is described from line 233 (Section 4.1.3), and the results are reported from line 358 (Section 4.3.3). In addition, we introduced a new evaluation metric related to Experiment 3 at line 284 (Section 4.2).

 

4. The GS is assumed to repeatedly flood the network over a reliable control channel, and UAV mobility follows a Gauss–Markov model. However, the robustness of the GS flood mechanism under highly dynamic or obstructed topologies, different mobility patterns, or partial GS connectivity is not thoroughly analyzed.

 

To better analyze the robustness of the GS flood mechanism under dynamic topology changes and partial GS connectivity, we added a new time-series metric and figure at the end of Section 4.3.1.

 

Specifically, we introduced the GS flood coverage rate plot (Fig. 15) to visualize, for each GS flood, the fraction of UAVs that successfully acquired routing information from that flood. We added the following description:

 

> Fig. 15 shows, for the case of 40 mobile nodes, 5 data streams, and a node speed of 20 m/s, the fraction of nodes that successfully acquired routing information from each GS flood. The solid line represents the average value over 10 runs for each GS flood sequence, and the dashed line represents the overall average across all runs. The coverage ratio drops sharply at certain intervals, indicating that the GS flood may not sufficiently propagate under highly dynamic topology changes or temporary network partitioning. Nevertheless, in many intervals, the coverage ratio remains approximately 70%.

 

This addition makes explicit that GS flood dissemination is not always successful in highly dynamic or temporarily partitioned topologies, rather than assuming perfectly reliable connectivity.

 

5. The quality of the figures is not satisfactory, as they are too small and difficult to read.

 

Thank you for pointing this out. We revised the figures to improve readability by increasing the font size (axis labels, tick labels, and legends) and adjusting the overall layout/scale.

 

6. The contributions should be presented more clearly, preferably using a bullet-point list, to allow the reader to easily identify the main proposals of the paper.

 

To present the contributions more clearly, we added a bullet-point list summarizing the main contributions of this study at line 97 (Section 1).

 

> The main contributions of this study are as follows:

• We proposed a DSR-based routing scheme for FANETs in disaster scenarios, aiming to improve the reliability of uplink communications from UAVs to the GS.
• We designed a mechanism in which UAVs can efficiently obtain fresh routes to the GS by introducing the GS flood option, where the GS periodically disseminates routing information.
• We enhanced operational flexibility by combining data buffering when a route is unavailable for forwarding over a satellite link when necessary.
• Through NS-3 simulations, we conducted a comparative evaluation against the existing schemes in terms of PDR, latency, control-packet overhead, and throughput.

 

 

Thank you very much for reviewing our work

 

Best regards,

 

Kaoru Takabatake

Tokyo University of Science

Email: k.tus@pass.netsecretinbox.com

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

General comments

The article proposes an ad-hoh network with a novel routing protocol that anticipates the periodical dissemination of routing information from the ground station (GS) to the set of unmanned aerial vehicles (UAVs) enabling each UAV to efficiently acquire fresh source routes to the GS. By using this protocol, the proposed network (FANET) can achieve a higher packet delivery ratio which may be crucial in case some kind of disaster has to be handled.  

The content of the article is within the scope of the Journal.

The main contribution of the article is the proposed routing protocol and the associated ad-hon network.

The article provides a sufficient literature review mainly included in sections 1 and 2. Section 3 describes the proposed protocol while section 4 presents the experimental results regarding the application of the protocol including a comparison with existing relevant protocols. In section 5, the obtained results are discussed while section 5 concludes the article.

A merit of the work is that it presents actual experimental data. In experiments 1 and 2, the proposed protocol is compared with representative existing protocols (that seems to outperform) regarding Packet Deliver Ratio (figs. 7, 10, 12, 15 and 16) and Latency (figs 8, 9, 11,13, 17 and 18). Experiment 1 also includes a positive comparison with regard to the number of generated IP packets. Experiment 3 regards a comparison of the throughput of the proposed protocol with that of Starlink, which also seems to outperform (fig. 19).   

Specific comment

A short paragraph should be added at the end of section 1 to describe the content of the rest of the article.

A short appendix with a brief explanation of what the HeMsc0, HeMcs2 and HeMsc7 data modes represent would be useful.

Use of English

The article is well written so, regarding the use of English, a minor editing would be sufficient.

Review decision

The article presents a novel routing protocol and provides a detailed experimental evaluation through several essential performance metrics. In most respects, the proposed protocol seems to outperform representative relevant ones. Given the above, I consider the article publishable subject to the minor-type revisions proposed above.

Comments on the Quality of English Language

The article is well written so, regarding the use of English, a minor editing would be sufficient.

Author Response

Dear Reviewer,

 

Thank you for taking the time to review our work.

We have followed all the suggestions provided. We have bolded all your comments. We have also written our response below each comment.

 

1. A short paragraph should be added at the end of section 1 to describe the content of the rest of the article.

 

Thank you for this suggestion. We added a short paragraph at the end of Section 1 (around line 107) that outlines the organization of the rest of the paper.

 

> The remainder of this paper is organized as follows. Section 2 reviews related works. Section 3 describes the proposed method. Section 4 presents the simulation settings and results. Section 5 discusses the results. Section 6 concludes the paper and outlines future work.

 

 

2. A short appendix with a brief explanation of what the HeMsc0, HeMcs2 and HeMsc7 data modes represent would be useful.

 

We added the following sentences below Table 6 (around line 255) to clarify the meaning of data modes.

 

> In NS-3, 12 data modes were implemented for IEEE 802.11ax (HE), ranging from HeMcs0 to HeMcs11. The trailing number in HeMcs0, HeMcs2, and HeMcs7 corresponds to the modulation and coding scheme (MCS) index for IEEE 802.11ax (HE) in NS-3. An MCS specifies a combination of a modulation scheme and a forward error correction coding rate; a higher MCS index provides higher spectral efficiency but requires better received signal quality (e.g., higher signal-to-noise ratio).

 

3. The article is well written so, regarding the use of English, a minor editing would be sufficient.

 

We had the manuscript professionally proofread by an English editing service, and we revised various sentences throughout the paper to improve grammar, clarity, and readability.

 

 

Thank you very much for reviewing our work

 

Best regards,

 

Kaoru Takabatake

Tokyo University of Science

Email: k.tus@pass.netsecretinbox.com

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

The authors have improved the quality of the paper by addressing the reviewers’ comments. The manuscript can now be considered for publication, provided that the following minor concerns are addressed:

1. The figure captions need to be improved (see Fig. 21).

2. In Fig. 1, the representation of the BS resembles a high-voltage pylon.

3. Please check the arrows in the flowchart in Fig. 3. Why does the first arrow from “Data packet generated” have a bidirectional direction?

4. Please check the punctuation in the equations.

Author Response

Dear Reviewer,

 

Thank you again for your careful review and helpful comments. We appreciate the reviewer’s time and effort in reviewing our revised manuscript for the second time. The reviewer’s additional feedback has been very helpful in further improving the quality and clarity of our paper.

We have followed all the suggestions provided. We have bolded all your comments. We have also written our response below each comment.

 

1. The figure captions need to be improved (see Fig. 21).

 

We revised the caption of Fig.21 as follows:

 

> Figure 21. PDR comparison with CHNN-DSR: reported in [36] (dashed) and reproduced results (solid).

 

2. In Fig. 1, the representation of the BS resembles a high-voltage pylon.

 

We updated the icon in Fig. 1 and clearly labeled it as the Ground Station to avoid confusion.

 

3. Please check the arrows in the flowchart in Fig. 3. Why does the first arrow from “Data packet generated” have a bidirectional direction?

 

The bidirectional arrow was unintended. We corrected it to a unidirectional arrow.

 

4. Please check the punctuation in the equations.

 

We checked the equations and standardized the formatting by adding periods at the end of equations. (1)–(4).

 

Thank you very much for reviewing our work

 

Best regards,

 

Kaoru Takabatake

Tokyo University of Science

Email: k.tus@pass.netsecretinbox.com

Author Response File: Author Response.pdf