Spoofing Traction Strategy Based on the Generation of Traction Code

Round 1

Reviewer 1 Report

This manuscript proposes a spoofing traction strategy to reduce the distortion in the induced process. The idea is interesting and well structured. The simulation and experiments demonstrate the effectiveness of the proposed strategy. However, the manuscript needs a considerable revision before it could be accepted. Here are some examples:

(1)    The full name of the abbreviation should be given when it first appears, e.g., TOA, GNSS, CNR.

(2)    There's an extra v at the end of equation (1).

(3)    In Figure 5, R_rl andR_sl are not defined before the Figure.

(4)    In page 5, column 138, “The maximum spoofing power introduced by….”. I think this sentence is misleading.

(5)    In Figure 6 and Figure 7, more parameters of the simulation should be provided, e.g., v_drag, h.

(6)    In figure 7(d), what are cd_l and cd_sp?

(7)    In equation (14), why R_sl is not related to the delay tao?

(8)    In equaton (15), R has not been defined in the manuscript.

(9)    In equation (16), what is C_l(t)?

(10)More details should be provide about equation (18) and (19). How to derive them?

(11)In Figure 14 and Figure 15, more parameters of the simulation should be provided, e.g., v_drag, h.

(12)What is SDR in the title of Figure 14?

 

Author Response

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Reviewer 2 Report

A) The first main comment regards the structure of the paper. It is very difficult to follow the rationale of the work, in particular it is not clear which is the target of the study since the beginning of the paper:

1) as first example if the authors want to design a spoofing attack (generation of the spoofing signal) or a spoofing detection (at receiver level) or both of them, considering that spoofing shal be such that not to be detected.

 

2) as second example, it is not clear which part of the spoofing generation is focused in this work. part of this is descoped, as reported, but please clarify/highlight which is the part covered in the paper and if it represents a novelty or typical.

3) clarify proposed strategy differences w.r.t. strategy 1 and 2, considered traditional ones. Add also reference for the traditional ones.

4) the Results shall be clarified and better structured. The figures of merit need to be shown such to understand the pros and cons of the proposed strategy w.r.t. the traditional ones 1 and 2. Table of results is good, but it is difficult to see the effective gain. As example, percentage RMSE could be used instead of absolute value.

5) conclusions are a good example of synthesis.

B) Other major comments are linked to the level of signal to noise ratios used for analysis.

1) It is not clear if reported levels are C/N0 in dBHz, C/N in dB or something else. Please correct/clarify.

2) C/N0 equal to 40, 50, 60dBHz are likely reported, please consider that also coherent time or integration time Tcoh shall be also reported. Note that Tcoh is used but not defined in the text. It shall be defined at the beginning, after used.

3) The C/N0 levels seem tool high for nominal conditions. Range between 30 and 50 maximum seems more realistic. Instead if C/N is reported, the levels under study are even too high. Typically, spoofer signal power is similar to authentic one, or as maximum +3dB than the genuine one.

C) The simulated scenario shall be better explained, in terms of time slots and generated conditions. Example, time start of the spoofing generation, time for the change of spoofing code rate/frequency or other signal parameters; expected times and effects on the received signal and receiver estimated parameters;

 

D) Clarify the traction code definition. The scope of the traction code is not clear. Who generates the traction code and the relationsheep with signal to be spoofed.

E) Paper needs a strong review and rewriting: structure, readability, english. Most of the formulae are not clear, with parameters not defined. It is difficult to follow the rationale for which expressions are reported.

Author Response

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Reviewer 3 Report

AoA based detection should also be mentioned in the introduction as a feasible anti-spoofing technique, even if it considered out of scope for the article. 

 

On page 5 the assumption is made that the target receiver uses a 1 chip spacing for early minus late correlators. It might be a good idea to repeat the analysis with a narrower chip spacing to address the existence of narrow correlator implementations and pulsed-aperature correlators that would be expected to behave more like a narrow correlator than a traditional one. 

 

While the authors have done a generally good job in writing the paper, a review round for English editorial comments could be a good idea as some of the phrasing or terminology might be improved. For example on line 216 the expression 'Due to the adoption of completely different traction thoughts, ...' is used. I think I understand this to mean due to the use of different traction strategies or approaches, but the word use makes it ambiguous.

The effectiveness of the strategy is clearly shown by the comparative SDR outputs.

Author Response

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Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

No further comments.

Author Response

Thank you for your review. It's been a pleasure to communicate with you. Your valuable suggestions have greatly improved the article.

Reviewer 2 Report

An improvement has been performed w.r.t. previous version, even if some clarifications are requested within the text.

The structure of the paper is more organized, but it is still not easy to be read. It is strongly suggested to work on this in next versioning.

In particular it is suggested to recall same objects with the same naming, to make coherent the text. Example of this can be the proposed strategy name (strategy 3, innovative strategy, else).

The simulations seem to be performed without noise and with noise, with different C/N0 levels.

Please find below some typos to be corrected and clarifications requested:

- line 114: figure 5 instead of figure 2 (typo)

- figure 8: not clear the "Transition process of traction code sequence". Please describe initial, intermediate and final form of traction code. They are not defined in the text. This part seems still not clear.

Proposed traction code seems to be equal to the difference between the spoofing wanted code delay and the authentic signal code delay. In such a way, the authentic signal (if estimated in phase, code and frequency) should be removed from the received signal. This assumption seems unrealistic. Please clarify in the text if this is the correct understanding.

- lines 166, 167:  gray ==> grey area (typo). Green and grey areas cannot be distinguished in the figure. Please update text or figure.

- The authors highlight that generation method of the traction code represents a novelty, but 1) which is the traditional method for the generation of the traction code? please complement in the text. 2) the code so generated seems to have exactly the same amplitude of the authentic signal. This means an accurate estimation of the authentic power level at antenna level. please complement in the text.

- line 216: tc is recalled, but not used in the equations (25) and (26)

- traction duration 1-(1+tc) is lower than zero (negative). To be updated.

- RMSE0 in equation (32) to be defined in the text.

- can you clarify the differences between results in section 3.1 and 3.2? it seems that only noise has been added in simulations of 3.2 section w.r.t. 3.1 one. Update and clarify in the text differences between them, maybe in 3.2 section introduction.

- “In Tables 4–8, it can be observed that the observations’ maximal RMSE percentage 412 change in the proposed strategy is 3.45%, while those of Strategies 1 and 2 are 679.57% 413 and 10872.48%, respectively.” It is suggested to report the trend of the statistics and not the exact values % again in the text. This is again reported in lines 468 and 469, to be updated.

- “In Table 4, because the 30 dBHz C/N0 is already a very weak GNSS signal, the meaning of the obtained results is very limited. It can also be observed in Figure 19 that the received results are very poor.” Can you extrapolate the sensitivity of the strategy 3 from these results or complement with further information on this topic? 60dBHz seems a too easy working point.

 

Author Response

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Author Response File: Author Response.docx