A Novel Random Access Algorithm for Very High Frequency Data Exchange (VDE)
Round 1
Reviewer 1 Report
The authors can check the review comments in the attached file.
Comments for author File: 
Comments.pdf
Author Response
Journal: JMSE (ISSN 2077-1312)
Manuscript ID: jmse-689985
Type of manuscript: Communication
Title: A Novel Random Access Algorithm for Very High Frequency Data Exchange (VDE)
Authors: Yi JIang , Yang Zheng * , Junsen Wang
Dear Reviewer,
On behalf of my co-authors, we appreciate very much for your constructive comments and suggestions on our manuscript. Those comments are all valuable and very helpful for improving our manuscript. According to the suggestions and comments, we have tried our best to revise the paper. We hope these revisions could meet with the approval. All the revisions were marked in blue in the manuscript. The details of the revisions in the manuscript are explained point by point as follows:
Reply to Reviewer
The paper has already been corrected for the grammatical errors throughout.
In Fig. 7 and Fig. 8, the packet collision ratio and the packet loss ratio for the continuous slot map drastically increase when the load is high. However, the results of Fig. 6 show that the continuous slot map shows better normalized throughput than that of ATL-CRDSA even when the load is over 1.0. More explanations are needed to justify the performance results.
Thank you for your suggestion on this issue. We have added some explanations to explain this situation, referring to 313-314. In VDE slot map, the RACH resource is very limited. The available slots in continuous slot map environment is much more than the VDE slot map environment. Under the same load, it can be proved that more deadlocks will occur (like P4 and P5 in Fig.4) when the channel resource is insufficient. An increase in this situation can result in a decrease in the normalized throughput of the system.
I believe that the proposed algorithm controls load based on the equation (11). The authors need to clearly define Gm. Which Gm value is used in the simulations? How the performance of proposed algorithm changes according to Gm values?
The explanation of the Gm has been added according to the comments, referring to LINE 273-274. The Gm is the optimal average load corresponding to the Tmax. When the average load exceeds Gm, competition intensifies and the increase of G will greatly add the probability of signalling packet collision. The throughput of the whole system will be rapidly degraded.
If the value of Gm is settled very small, then when the system does not reach the optimal load, the shore-station will determine pATL according to the ratio of GM/G when G exceeds Gm. When the mobile stations receive the pATL , they will give up sending the message with 1-pATL probability, resulting in a waste of resources in the system.
If the value of Gm is settled very big, the system will run to optimal throughput first. With the increase with G the throughput of the whole system will be rapidly degraded. When G exceeds Gm, the shore station will broadcast the pATL to make the whole system work at load for Gm. In this case we can’t get the optimal throughput.
With the proposed algorithm, the shore station broadcasts when the load exceeds Gm. Is the overhead due to the broadcasting acceptable? The overhead issue due to the broadcasting needs to be added. I believe that it can make the results more convincing.
Thank you for your interest in the overhead issue. Load control is one of the most important parts in this paper, which we must discuss. In the VDE application, some time slots are fixed allocated to the shore station and some are allocated to the mobile stations. For slots allocated to TBB channels and ASC, even if the state of the time slots is “Free”, the mobile stations cannot apply for occupation. Therefore, in the VDE time slot access algorithm, the mobile stations can only use RACH to access the channel.
Under this premise, the shore station can broadcast Gm and pATL through TBB channel, which will not burden the RACH. Due to the limited number of ships entering and leaving the port per minute, the broadcasting of Gm and pAT at the beginning of each frame completely meets the system requirements.
The authors add reference numbers in the []. For example, in the line 31 of page 1, the sentence of “~~ concept of VDES 1.” need to be revised to the sentence of “~~ concept of VDES [1].”
We have already replaced “~~ concept of VDES 1.” with “~~ concept of VDES [1]. ”, referring to LINE 31.
Sincerely Yours,
Mr. Yang Zheng
Reviewer 2 Report
First, I have a need to say that I am honored to have received such a great paper for a review process. This paper is written in good scientific and technical manner. The research problem is given in the introduction, following with the related work and description of a novel RACH algorithm and in the end providing, analyzing and concluding the simulation results. The main scientific contributions of the paper are the allocation of each slot in the VDE frame and construction of a new slot map. In addition, the new RACH algorithm is provided with the simulation results and performance evaluation.
However, there is a lack of MATLAB simulation model description. Additionally, in the performance evaluation section there might have been different simulation scenarios, e.g. different number of mobile stations, etc.
Also, there need to be corrections in reference numbers in the text. Refer to Instructions for authors: „In the text, reference numbers should be placed in square brackets [], and placed before the punctuation …“
The following is a list of remarks, comments and suggestions for specific lines of the text.
LINE 29: Automatic identification system (AIS) has two channels, AIS 1 and AIS 2, so both channels had been overloaded in some parts of the world. Refer to ITU Report ITU-R M.2287.
LINE 33: What are these novel maritime services in e-Navigation? If they are mentioned, they should be listed in text.
LINE 34: Again, both channels of AIS. Refer to comment for LINE 29.
LINE 40: According to [Reference number] …
LINE 47: Instead of random access channel access algorithm it should be RACH access algorithm, since it was abbreviated earlier in the text.
LINE 50 – 56: This whole paragraph is redundant, since it is not clear what is VDES resolution, who will adopt it and is it confirmed information. Additionally, it is not clear what will lay the policy and technical foundation for the VDES application.
LINE 57: It is not clear what is the point of this sentence and what is the equation of VDE technical specifications.
LINE 59: It is not clear enough which characteristic is refering to. First full name, then abbreviation – Slotted-ALOHA (S-ALOHA).
LINE 65: Refer to the comment for LINE 40.
LINE 69: Is there always a very large number of mobile stations nearby the shore station?
LINE 82: Refer to the comments for LINE 40 and LINE 65.
LINE 92: MAC has already been introduced in the abstract, so the full name is redundant.
LINE 109: Is this percentage a verified information? What is the reference for this information?
LINE 114: O instead of 0 in word ALOHA.
LINE 127: Brackets for units can be omitted.
LINE 139: ECRA instead of ERCA.
LINE 143 – 144: Suppose this should have been only one sentence.
LINE 153: Is it spectral sufficiency or efficiency?
LINE 172: Refer to the comments for LINE 40, LINE 65 and LINE 82.
LINE 177: It is not clear in which way are time slots synchronized by the UTC.
LINE 283: In the equation (10), what does the Gm stand for? It is not stated in the text.
LINE 289: In equation (11) there need to be commas or words separating values and conditions.
LINE 294: It is not clear enough what δ(t) indicates. Is it Dirac delta function or some random probability density function?
LINE 297 – 299: In Figure 5., pATL is somewhere small and somewhere capital letter. This needs to be corrected.
LINE 310: Letter T is redundant since it is already explained what it stands for.
LINE 313: Letter T, the normalized throughput, should be italic like everywhere else in the paper.
LINE 314 – 315: Refer to the comment for LINE 127.
LINE 326: The dot at the end of figure name is redundant.
LINE 328: Refer to the comment for LINE 313.
LINE 335: Refer to the comment for LINE 326.
LINE 337: There is different font for letter G.
LINE 352: The IIC is already described, so the full name is redundant.
LINE 373 – 374: This is probably invalid reference name.
LINE 377-378: Missing data on the given link. This is probably ITU, ITU-R M.2092-0, Technical characteristics for a VHF data exchange system in the VHF maritime mobile band, Electronic publication, 2015
LINE 426: There is already 3rd edition available for the reference number [28].
Author Response
Journal: JMSE (ISSN 2077-1312)
Manuscript ID: jmse-689985
Type of manuscript: Communication
Title: A Novel Random Access Algorithm for Very High Frequency Data Exchange (VDE)
Authors: Yi JIang , Yang Zheng * , Junsen Wang
Dear Reviewer,
On behalf of my co-authors, we appreciate very much for your constructive comments and suggestions on our manuscript. Those comments are all valuable and very helpful for improving our manuscript. According to the suggestions and comments, we have tried our best to revise the paper. We hope these revisions could meet with the approval. All the revisions were marked in blue in the manuscript. The details of the revisions in the manuscript are explained point by point as follows:
Reply to Reviewer
The paper has already been corrected for the grammatical errors throughout.
However, there is a lack of MATLAB simulation model description. Additionally, in the performance evaluation section there might have been different simulation scenarios, e.g. different number of mobile stations, etc.
Thank you for your suggestion on this issue. We have added related simulation and analysis in Section 4.4. We compared the normalized throughput of ATL-CRDSA with different number of ships (200, 400, 600). Moreover, we discussed the effect of the number of mobile stations on the algorithm.
LINE 29: Automatic identification system (AIS) has two channels, AIS 1 and AIS 2, so both channels had been overloaded in some parts of the world. Refer to ITU Report ITU-R M.2287.
LINE 34: Again, both channels of AIS. Refer to comment for LINE 29.
1) Thank you for your suggestion. We have already replaced "AIS channel" with "AIS channels (including AIS1, AIS2) overload in some ports has become an urgent problem to be solved with the increasing traffic [1]", referring to LINE 29-30. [1] refers to ITU Report ITU-R M.2287.
2) We have already replaced "channel" with "channels", referring to LINE 36.
LINE 33: What are these novel maritime services in e-Navigation? If they are mentioned, they should be listed in text.
“, such as transmission of hydrology, weather forecast, other non-navigation application message, and the VDE band can be used to transmit any data.” has been added, referring to LINE 34-35.
LINE 40: According to [Reference number] ...
We have already replaced “ITU Recommendation M.2092-0” with “[4]”, referring to LINE 42, 62, 78, 171.
LINE 47: Instead of random access channel access algorithm it should be RACH access algorithm, since it was abbreviated earlier in the text.
We have already replaced “random access channel” with “RACH”, referring to LINE 49.
LINE 50-56: This whole paragraph is redundant, since it is not clear what is VDES resolution, who will adopt it and is it confirmed information. Additionally, it is not clear what will lay the policy and technical foundation for the VDES application.
Thank you for your suggestion. After discussion on this, we deleted the whole paragraph to make the content more concise and coherent.
LINE 57: It is not clear what is the point of this sentence and what is the equation of VDE technical specifications.
We have already replaced “With the equation of VDE technical specifications” with “With the technical specifications of VDES update”, referring to LINE 51-52. We listed details like band width, frequency resource sharing and time slot functions. These details are important technical indicators of link layer which forms the basis of our research project. And it is very important for us to define a new time slot mapping model and to choose which type of access algorithm.
LINE 59: It is not clear enough which characteristic is referring to. First full name, then abbreviation-Slotted-ALOHA (S-ALOHA).
LINE 177: It is not clear in which way are time slots synchronized by the UTC.
The explanation has been added beforehand according to the comments, referring to LINE 52-56. According to ITU Recommendation M.2092-0, the VDES frame structure is synchronized in time to GPS Coordinate Universal Time (UTC), synchronized other than UTC direct may be provided by the AIS. Each frame equals one minute and is divided into 2250 slots. A terminal can send data at any slot and VDE packet transmissions shall always fit into one slot. These two characteristics are very suitable for using s-aloha algorithm.
LINE 69: Is there always a very large number of mobile stations nearby the shore station?
We have listed some of the busiest ports in the world which are facing channel load problems, like in Shanghai, Victoria and Rotterdam, e.g., referring to LINE 65-66.
LINE 92: MAC has already been introduced in the abstract, so the full name is redundant.
Thank you for your suggestion. We have already replaced “media access control” with “MAC”, referring to LINE 88.
LINE 109: Is this percentage a verified information? What is the reference for this information?
The reference has been added according to the comments, this probability value is the data in reference [10], referring to LINE 105.
LINE 114: O instead of 0 in word ALOHA.
We have already replaced “0” with “O”, referring to LINE 110.
LINE 127: Brackets for units can be omitted.
We removed the brackets for all units in the article, referring to LINE 124, 313, 314, 324.
LINE 139: ECRA instead of ERCA.
We have already replaced “ERCA” with “ECRA”, referring to LINE 137.
LINE 143-144: Suppose this should have been only one sentence.
AFDA is an excellent algorithm for asynchronous systems. We have modified the description of the AFDA algorithm to make it easier to understand. The differences between AFDA and CRA, ECRA were also compared, referring to LINE 137-142.
LINE 153: Is it spectral sufficiency or efficiency?
We refer to 1139 to make a great modification to this part and to introduce the mechanism of ACM to maximize normalized throughput and minimize packet error rate, referring to LINE 153.
LINE 283: In the equation (10), what does the Gm stand for? It is not stated in the text.
The explanation of the Gm has been added according to the comments, referring to LINE 273-274. The Gm is the optimal average load corresponding to the Tmax. When the average load exceeds Gm, competition intensifies and the increase of G will greatly add the probability of signalling packet collision. The throughput of the whole system will be rapidly degraded.
If the value of Gm is set very small, then when the system does not reach the optimal load, the shore station will determine pATL according to the ratio of GM/G when G exceeds Gm. When the mobile stations receive the pATL , they will give up sending the message with 1-pATL probability, resulting in a waste of resources in the system.
If the value of Gm is set very big, the system will run to optimal throughput first. With the increase with G the throughput of the whole system will be rapidly degraded. When G exceeds Gm, the shore station will broadcast the pATL to make the whole system work at load for Gm. In this case we can’t get the optimal throughput.
LINE 289: In equation (11) there need to be commas or words separating values and conditions.
We have added the commas to separate values and conditions, referring to equation (11).
LINE 294: It is not clear enough what δ(t) indicates. Is it Dirac delta function or some random probability density function?
Thank you for your suggestion. indicates the Dirac delta function. In our model， the ideal environment is without delay. So we can get the probability density function by using the .
LINE 297-299: In Figure 5, pATL is somewhere small and somewhere capital letter. This needs to be corrected.
We have already replaced all “PATL” with “pATL”, referring to Figure. 5.
LINE 310: Letter T is redundant since it is already explained what it stands for.
LINE 313: Letter T, the normalized throughput, should be italic like everywhere else in the paper
LINE 337: There is different font for letter G.
We have already deleted the letter “T”, referring to LINE 308.
We have already replaced “T” with “T”, “G” with “G” referring to LINE 311, 329, 331, 332.
LINE 326: The dot at the end of figure name is redundant.
We have already deleted the dot at the end of the figures, referring to Figure. 6-8.
LINE 352: The IIC is already described, so the full name is redundant.
We have already replaced “iterative interference cancellation (IIC)” with “IIC”, referring to 366.
LINE 373-374: This is probably invalid reference name.
We have consulted relevant materials and selected new reference，referring to LINE 391-393.
LINE 377-378: Missing data on the given link. This is probably ITU, ITU-R M.2092-0, Technical characteristics for a VHF data exchange system in the VHF maritime mobile band, Electronic publication, 2015
Thank you for your suggestion. We checked the link and a new hyperlink was submitted, referring to 396.
LINE 426: There is already 3rd edition available for the reference number [28].
Thank you for your suggestion. We have already replaced “IALA G1139 Ed.1 Technical specification of VDES. Saint Germain en Laye, France 2017.” with “B. Technical specification of VDES, 3rd ed.; IALA. St Germain en Laye, France 2017.”, referring to LINE 447.
Sincerely Yours,
Mr. Yang Zheng
Round 2
Reviewer 1 Report
The authors have revised this paper according to the reveiwer's comments.
However, there are still minor issues which need to be revised. I recommand that the authors have to check the errors throughout this paper.
1. In line 41, 44, 51, 80, the unnecessary sentence "Error! Reference source not found" need to be removed from this paper. I believe that this sentence is type error.
2. The authors have to add the refererence numbers in []. For an example, in line 57~58, the sentence needs to be revised to "~ random access to some extent [7]".
Author Response
Please see the attachment
Author Response File: Author Response.pdf
