Empirical Performance Models of MAC Protocols for Cooperative Platooning Applications

Round 1

Reviewer 1 Report

The paper is overall nicely written and easy to follow. The topic of platooning, despite not novel, is still of interest and the authors add a small brick to the pack. The effort done by the authors to obtain curves fitting the impact of number of neighbors on channel busy ratio (CBR) and number of collisions is appreciable.

My main concern is that the output of the paper is not really of practical use in my opinion. First of all, all simulations are done with fixed packet size and frequency, which is not expected in reality and has a clear direct impact on the shown results. Second, it does not make much sense to derive the CBR as a function of the number of neighbors, as the former metric is much easier to obtain by a vehicle in practice; connected to this second observation, it would also be much simpler to derive the number of collisions from the CBR, instead that from the number of neighbors. Also to note that the channel is modeled as free space, maybe without channel variability due to fading, which also is not realistic and is expected to have a major impact on the results.

In addition to these main points, that need to be clarified by the authors, a few minor comments are as follows:

- (very minor) The citations to Plexe-Slot and RA-TDMAp could be added also in the Introduction, page 2, line 81;

- For the sake of completeness, in Section 2 it should be better to add at least a reference to the C-V2X technology (see, for example, "Survey and Perspectives of Vehicular Wi-Fi Versus Sidelink Cellular-V2X in the 5G Era") and its application to platooning (e.g., 3GPP C-V2X and IEEE 802.11 p for Vehicle-to-Vehicle communications in highway platooning scenarios");

- Probably a Typo: Page 9, line 306, I guess that "we collect four metrics" should be replaced by "we collect three metrics";

- Please define the "number of RF neighbors" explicitly; is it related to the received power? decoded messages? maximum distance?

- Please better specify the environment. How large is the simulated scenario? How large are the lanes? How long are the cars/trucks? Which is their speed?

- Please give an idea of the wireless range (for example, average range with maximum/minimum power);

- Please specify the channel model (fast/slow fading, if present);

- At page 14, lines 438-441, I suppose an effect of high power is that the leader messages are less reliable; this should be at least discussed.

 

Author Response

Please refer to attached rebuttal letter.

Author Response File: Author Response.pdf

Reviewer 2 Report

In this paper, some empirical observations are presented coming from different MAC protocols and showing the relationship between various network quality metrics and protocol-related or scenario-related parameters.

I find it interesting as a paper and as a concept, and I can see the merit of that, however, I would like to see a more extended comparison between different MAC protocols. At the moment, three protocols are compared (CSMA/CA, Plexe-Slotted, and RA-TDMAp), but a larger number of them is described in the introduction section. Why none of the other protocols was not considered during the comparison?

Apart from that, I believe that the results section is nice and the paper is generally, well written. There are few typos here and there in the text. A good proofreading is recommended.

Author Response

Please refer to the attached rebuttal letter.

Author Response File: Author Response.pdf

Reviewer 3 Report

This manuscript presents a model that can significantly mitigate packet collisions and busy time in various VANET scenarios and verifies its performance through simulation. However, the authors need to clarify some of the ambiguities below.

1. Since this manuscript highly depends on reference [16][18], the authors shall clearly address the difference between existing scheme and current proposals.

2. The authors shall explain the rationale for leader appointment.

3. Do all nodes maintains delay list? The authors shall explain whether there is any overhead (e.g. computation and piggybacking) when neighbor nodes increase or the number of collisions increases.

4. In line 314, the authors shall show the calculation method for Busy Time Ratio.

Author Response

Please refer to the attached rebuttal letter.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The authors have answered all comments with some argumentation. Even if I have a different opinion in some points and do not see a significant improvement of the manuscript, I think that more rounds would not be useful and there is thus no reason to further delay the publication of this work.

I suggest to proceed publishing the paper.