Global Navigation Satellite Systems Signal Vulnerabilities in Unmanned Aerial Vehicle Operations: Impact of Affordable Software-Defined Radio

Round 1

Reviewer 1 Report (Previous Reviewer 3)

The authors made the suggested changes.

Review punctuation and grammar.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report (Previous Reviewer 1)

This version of the paper is better than the initial one. Introduction is improved, more references are added, and the discussion and the conclusion are improved as well. Manuscript is also corrected in terms of typos and other minor errors.

However, main issues of this paper are still present. Authors present the conclusions based on only one test. Results did give some insights and tests on different GNSS signals would probably yield similar results, but tests should be repeated to confirm that.

Specific comment:

In previous version of the manuscript at lines 231-232 there was a sentence: Converting these moving points into a visual representation would result in a scatter plot. In this version this sentence is gone and there are no scatter plots either. What is the reason for that? It would be interesting to see these plots as a visual representation of the impact of jamming and spoofing to positioning.

Overall, the manuscript is improved, but major revision is still required.

The quality of the English is fine, some stylistic corrections could be done (some sentences are too long).

Author Response

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Reviewer 3 Report (New Reviewer)

This paper investigates the impact of SDR device-generated spoofing signals on the UAV GNSS positioning. I think this topic is interesting and the word is solid.

My coments are as follows:

- L27: Is timing an important issue for UAVs?

- L54: The dual- or multi-frequency GNSS positioning have been very common in civil applications, even in a cell phone.

- L293: Please correct the heading -- if? of?

- I believe that your manuscript can be better after polishing the english writing.

Author Response

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Author Response File: Author Response.pdf

Reviewer 4 Report (New Reviewer)

1. The submitted version is a draft. There are too many marks in the article, which affect the reading very much.

2. The core work of this paper is to use HackRF One to transmit fake GNSS signals, and the workload of this paper seems to be insufficient.

3. Some studies have proved that small SDR devices can deceive and capture UAV. This paper only assess the power and distance of the interference signal without experimental evaluation through the real UAV capture scene. In addition, in Section 2, the steps of generating and transmitting forged signals can be queried from the network. This article seems to be lack of innovation. This paper should be compared with the existing related work. 

Author Response

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Round 2

Reviewer 2 Report (Previous Reviewer 1)

Authors did address some issues as suggested, but some further corrections should be done:

1. scatter plots should be briefly described.

2. Authors added new measurements (shown in Fig. 11) but they should be  explained better. In present form these measurements do not contribute to the conclusions of the paper. I would suggest to perform second measurement again following the procedure applied in the first experiment.

The quality of the English is fine.

Author Response

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Author Response File: Author Response.pdf

Reviewer 4 Report (New Reviewer)

1. Section 2 should be core work of this paper. It contains the materials and methods. However,  Section 2 mainly introduces the steps of generating and transmitting forged signals. These steps can be found from the network.

2. The improvement is not enough. The core work is not improved. The workload of this paper still seems to be insufficient.

3. The response should explain how to solve each review comment.

Author Response

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Author Response File: Author Response.pdf

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

The manuscript deals with very interesting topic. Applied methodology is appropriate and well explained. Obtained results are also well explained and represented, and very applicable.

However, this manuscript has several issues which should be addressed by the authors.

Major comments

1. As stated, methodology is well described and appropriate, but authors conducted only one experiment, even though they had the resources to conduct more. Experiment should be repeated at least once more, but with different signal (e.g. GPS L2 C, GLONNAS G1…). This would provide more data to compare and analyze, and thus more reliable conclusions.

2. Section 5 (Conclusions) is too long, it should be more concise. Points presented there are fine and valid, but there is some repetition in the text. It seems like each author provided the conclusion and then they were compiled in one section, without editing and refining the text. Also, after addressing the comment 1, conclusions should be modified accordingly.

3. Authors did not explain the terms jamming and spoofing. These are basic terms for this manuscript and reader should not search for them in the literature.

Minor comments

1. If the figure is the original it is not necessary to write Source: authors.

2. ‘HackRF One by Great Scott Gadgets’ appears too often. After the first time it is mentioned just ‘HackRF One’ is clear enough.

3. Line 103                'The focus of this research centered…'  I suppose this should be: 'The focus of this research is centered…'

4. Line 119                'Research The methodology in this paper…' I suppose this should be: 'The research methodology in this paper…'

5. Line 152                Typo: '…reliable device in in selected…'

6. Line 168         ‘All the necessary information can be found on NASA webpage.’ Instead of this sentence authors should insert the link to webpage.

7. Lines 231, 232 ‘Converting these moving points into a visual representation would result in a scatter plot.’ I suppose it would be interesting to see scatter plots of the data authors obtained.

Generally, the quality of English language is fine, but it can be improved.

Reviewer 2 Report

This paper presents a Software-defined approach for GNSS Jamming in UAV applications. Generally, this is an interesting topic. However, this paper does not involve in-depth theatrical analysis and extensive numerical results. It is more like a user manual or test report. It does not introduce the challenges for SDR based GNSS jamming/spoofing, and also does not presents meaningful results. It mainly introduces how to use the open-sourced software ‘gps-sdr-sim’ and HackRF to broadcast GPS signals, which is far from talking about ‘GPS vulnerability’. Hence, I don’t think this paper contribute new knowledge to communities, which is not worth to be published in this journal.

It does not involve spacific research question, no methodology and only presents some demonstrative results, which is meaningless to support useful conclusion. Hence, I don't think this paper is worth to spend long time to give very detailed comments. We should admit that the GNSS jamming/spoofing is essentially critical for UAV applications, while this paper just tell how to use test the open source software 'gps-sdr-sim' using HackRF frontend. Basically it is only a low cost GPS simulator. It does not involve any theortical problem. In the numerical results section, it just demonstate I can receive the signal. It is nothing about GNSS jamming or spoofing. As a jammer, we have to address what is the new challenge to achieve GNSS jamming for the UAV users, or how to mitigate the potential jamming/spoofing. The numerical results does not involves the 'real GNSS signals' and interferences, so it cannot be called 'jamming' or 'spoofing'. There are a full set of GNSS interference theory and performance indicators, such as CNIR. Hence, the author only provide an attractive title, but its content is not about GNSS jamming and the author seems does not have enough background knowledge about GNSS jamming/spoofing. That is why I refuse to provide detailed comments.

There are many casual style expressions and also some grammar error，so moderate English editing is required.

Reviewer 3 Report

The paper offers a novel approach to examine the Spoofing, alongside jamming, of the Global Navigation Satellite System signal. The work is well laid out on the basis of a systematic protocol. There is definitely something interesting to find for many researchers interested in applications of this type.

Advantages:

The work is considered interesting and relevant to the scope of the journal. Researchers understand both the rationale and the methods and results.

Disadvantages.

1.          The introduction should better lend the objective of the paper in a more precise and summarized manner.

2.          The work has very few bibliographical references 17 should increase its theoretical support by at least 40 references.

3.          There are problems with the graphs, the way of presenting some of the results should be improved. Increase the size of the graphs so that they can be seen better.

4.          They should expand the discussion is too short.

5.          In the conclusions they could elaborate on challenges or better future implementation of these techniques.

In conclusion, the authors should improve the paper in several aspects to make it more understandable and suitable for publication.

Improve writing and punctuation in the document