Smartphone-Based Social Distance Detection Technology with Near-Ultrasonic Signal

Round 1

Reviewer 1 Report

Dear Authors,

please consider the following remarks when finalizing the article:

1. It is necessary to provide a reference to the source of formula (3).

2. [43] does not seem to be a reference to an article about human hearing.

3. The notation in formula (8) (v, vr, vs) needs to be explained.

4. It is necessary to give a signature on the y-axis in Fig. 23

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

The paper is an interesting piece of work on the topic of distance estimation based on wireless signals, here audio signals are used (inaudible for humans).

Strengths:

- The paper gives a very good overview of existing approaches and methods (BLE, UWB, etc.) and motivates the problem of inaccurate estimates well.

- The paper provides real experiments and presents the results clearly.

Weaknesses:

- It is not clear why new MAC algorithms are needed for the purpose of the work. If it is not really needed, I suggest to omit this aspect in this work.

- The experiment cases are limited to a few basic cases, yet in real setting, more complex constellations are expected.

Detailed comments:

- The cited works are relevant, yet I recommend to have a look at the following recent related work and include it in the related works section:

[1] B. Etzlinger, B. Nußbaummüller, P. Peterseil and K. A. Hummel, "Distance Estimation for BLE-based Contact Tracing – A Measurement Study," 2021 Wireless Days (WD), 2021, pp. 1-5, doi: 10.1109/WD52248.2021.9508280.

[2] D. J. Leith and S. Farrell, \Coronavirus Contact Tracing: Evaluating the Potential of Using
Bluetooth Received Signal Strength for Proximity Detection," SIGCOMM Comput. Commun.
Rev., vol. 50, no. 4, pp. 66-74, Oct. 2020. doi: 10.1145/3431832.3431840.

- page 4, UWB: It is true that few phones have UWB, but in the future, this may change. In [2] (see above), there is also a description about the potentials (and drawbacks) of UWB. I suggest to extend this section by a discussion of UWB as UWB is indeed a promising and relevant ranging technology.

- Section 3: Here, Microsoft BeepBeep is described, yet it is not clear which parts of this system are used and where own technology is applied. This needs to be clarified.

- Section 3.3: Figure 12 should be described in the text, i.e. what is provided by each of the steps (briefly).

- Experiments: How many runs have been conducted in each of the cases? Maybe I missed it but this should be clearly stated.

- Figure 23 and text: I assume that the error is given in meters (unit should be added to the figure). How is the error calculated? We see here a negative error, which is kind of misleading (e.g., assume two error values of 2 m and -2 m respectively, leading to a median/average error value of 0 m). I suggest to discuss the error in terms of a positive distance error.

Editorial:

- page2, line 84,85: "the system has little argument about the NLoS system" -- I suggest to reformulate and avoid "has little argument".

- Some figures and captions are not centered, I guess they should be in the CR version.

- I suggest also to use a space between the number and the unit Hz, e.g., page 11 "19250Hz" --> 19250 Hz.

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

Overall contents and materials provided is good.  Paper Organization is also good.  Some suggestions are as under: 

 (Page 6 line no:  206)   “Optimazed Signal Designed”   title needs revision.

 

(Page 6 line no:  211):    it is reported that “Figure 5 shows the frequency responses of different commercial mobile phone microphones.”   Give experimentation details

(Page 6 line no:  215):  it is reported that “According to the results, this paper uses the acoustic signal frequency range of 18KHz-23KHz…”   which results are being referred? Give proper reasons or referencing.

 

 (Page 7 – line 230)  “The theory relationship between hearing threshold and frequency is shown as….” Give citation or Justify reasons for parameters’ selection for equation (3).

 

(Page 8 – line 253)   In order to solve low-frequency leakage problem, the waveform of the chirp signal is reconstructed, and the window of Blackman window and rectangular window is used. Justify the selection of window(s).

Author Response

Please see the attachment.

Author Response File: Author Response.pdf