Design and Performance Analysis of Navigation Signal Based on OFDM

Round 1

Reviewer 1 Report

The abstract contains a very long introduction of the problem and the information on what is within the paper starts in the third sentence. The introduction in the abstract should be shortened.

Some sentences are hard to understand, even in the abstract - e.g. the sentence in lines 16- 20, which finishes with a comma and lists many technologies without a clear definition of what is proposed within the paper.

The motivation of the paper is not sufficiently discussed, especially in relation to the results presented in the performance evaluation. The idea of using OFDM for localization is not novel, which is also apparent from the literature review section. It can be improved and the paper shows an interesting idea on how to change the signal to improve the autocorrelation and phase shift calculation, but it would be beneficial to provide a more clear description in the introduction section showing the motivation of the research.

The performance evaluation is thorough and considers various factors, from accuracy to resiliency to multipath error, which is very good. However, the comparison between the proposed signal and traditional methods shows the lower bound of the accuracy, not the average or median accuracy. It would be interesting to see those or discuss how the average accuracy can be compared to other methods.

Most of the figures are not centred and not appropriately aligned with the text.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

The article is devoted to the actual topic of improving the quality of the navigation signal. The theme of the article corresponds to the general goal of the Applied Sciences. The article is written in a good technical language and can be published after a minor revision.

Main observations:

1. The abstract should be rewritten. Its first part (Lines 10-16) should be moved to the Introduction. In the rest of it, the main technical achievements of the work should be added.

2. The article uses abbreviations (acronyms) very often, which makes it difficult for the reader to perceive many of the provisions. I agree that it is impossible to repeat many times the full names of techniques, filters, etc. However, some balance between acronyms and names should be maintained.

3. Orthogonal frequency-division multiplexing (OFDM) is a well-known type of digital transmission and a method of encoding digital data on multiple carrier frequencies. The use of OFDM in the improvement of signal quality in the global satellite navigation system can be welcomed. However, the article pays little attention to the history of OFDM development. In particular, there are no references to the works of Robert Chang (1966, 1970), Weinstein and Ebert (1971) and other original articles. The authors should conduct a revision of the literature used.

4. There is no reference to the mathematical formulas used. For example, The mathematical expression of an OFDM symbol (formula 1), no reference to the source Figure 1. OFDM frame structure diagram, etc.

5. In our opinion, the analysis of the autocorrelation function (ACF) and power spectral density (PSD) is insufficiently reasoned. The expression "experimental data show..." is not an argument in characterizing the results.

6. There is no analysis of the application of OFDM filters, it is not explained how the experimental conditions under which «the length of CP is changed and successively set as   Tg = (10, 20, 32, 64) Δt »

7.  OFDM requires very accurate frequency synchronization between the receiver and the transmitter. There is not much information on this subject in the manuscript.

8. No meaningful signal-to-noise ratio analysis

9. It is necessary to revise the conclusions, making them more technically accurate. In the present form, the conclusions only postulate the results, without giving any technical specifications.

10.  Finally, the text requires a little revision of the English language

Author Response

Please see the attachment.

Author Response File: Author Response.pdf