High-Resolution Delay Spread of Wide-Band Wireless Link in Long Tunnels—Theory and Experimental Verification
Round 1
Reviewer 1 Report
The presented research is interesting, and, in my opinion, the experimental results verified by simulation/theory should be welcomed. But there are several flaws with the research and problems with the manuscript itself.
1) The impulse response h(t) is the key factor that is used to evaluate DPD, RMS DS, etc. And it is evaluated assuming that "... the antenna’s gain is not dependent on the frequency" (see line 80). But this is not the case for the utilized antenna (JXTXLB-10180)! It varies in the chosen frequency range by more than 5.5 dB! (see https://manualzz.com/doc/30605066/antenna-products)
It makes the results questionable and thus must be cleared out.
2) Authors must explain the derivation of (1), since in [19] this equation is absent, and in [20] it is given in either power ratio (eq. (1) in [20]) or field ratio (eq. (11) in [20]). But in the last case, there is a specific phase shift that impacts delay time, which is not considered in the presented research.
3) The last sentence:
"To conclude, our findings suggest that unless working with abnormally high data rates, wireless communication in pedestrian tunnels is possible with close to zero interference.",
is a mere assertion (and a very strong one), which is not supported by any arguments. Thus it should be commented or prooved.
4) Literature review must be expanded since there are plenty of works devoted to this topic (including the prespecified frequency range). The obtained results must be compared with the existing ones.
5) Formatting, typoes, grammar and word choice. E.g.,
What do indices "i" and "j" in (1) correspond? "j" is already reserved for the imaginary unit!
line 68: ". [21]."
line 69: ", G,"
line 78: "Dt" is not defined, it should be "Dt"
line 210: "Equation 12", should be "(12)"
line 228: capital letter in the middle of a sentence,
etc....
6) Fig 1 is absolutely uninformative since no simulation setup is described. It is advised either remove it or present the simulation parameters.
Author Response
Please see the attachment
Author Response File: 
Author Response.pdf
Reviewer 2 Report
In the manuscript "High-resolution Delay Spread of Wide-band Wireless Link in Long Tunnels - Theory and Experimental Verification," an extensive analysis of delay spread was done for the narrow and straight pedestrian tunnel. The outcome is noble, but it has some flaws.
<Content>
1: In the ray tracing model, how many rays are used? Is there any relation between the number of rays and the simulated results?
2: Why do the PDP profiles not match well with the measured and the ray tracing model (Fig. 7) at 20-meter and 45-meter distances?
3: In the manuscript, there are explanations for why the RMS delay spread decreases as distance increases along the straight tunnel. But how to explain the first valley of decreasing value after 10 m, and then value rises? How do you explain this phenomenon?
4: The channel measurement setup is not described well. The antenna is described, but the transmitter and receiver formation is not well documented.
<Format>
1: Throughout the manuscript, every unit is written like 1GHz, 0.5nsec, but the standard convention is to write as 1 GHz, 0.5 nsec (the authors also used this style in Table 3)
2: In Figure 5 (b) caption capitalization rule is not followed
3: Figure 1 caption was started with a small letter.
4: What is the meaning of the used symbol in the x-axis in Figure 1?
5: Unnecessary capital letter use for article (line 51, 228, 238)
6: Figure 4 is not displayed well; it seems part of it is cropped?
7: Table 3, the unit of frequency is not capital K; it should be a small letter k.
8: Figure 7 caption- capitalization rule is not followed
Author Response
Please see the attachment
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
After the changes made by the authors, I think the submission can be accepted in the current form.
