Priority Based Channel Searching Sequence Allocation for Rendezvous of Cognitive Radio
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThis is a paper focusing on a attempt to provide a more efficient way to handle secondary calls within a cognitive radio. it has a nice flow and is understood but seems to fall short of describing the whole idea/implementation. it is short but concise; something of a good thing.
the intro is well written and can be understood by the reader
i couldn't find any "background research" or "state of the art" in the first part. authors have to explain what similar techniques have been attempted so far and how successful they were.
in chap 4, mention the simulation tool and testbed (i.e. s/w and h/w used)
understanding that it might be difficult, i wonder if the authors could also do some practical experimentation on this and then compare with the simulated results. experience shows that these two are often very different.
1. Main question addressed by the research
- The research question is set but not explicitly: can a sequence design (like a priority driven rendezvous system in a frequency hopping sequence) be used to increase efficiency in cognitive radio? This should be better emphasised. There are also 3 objectives laid out clearly
2. Originality and Relevance to the Field
- As cognitive radio is a fascinating subject, any improvement in the priority algorithm is of major importance. The study does make clear the necessity of this but fails to prove why the competing systems are inadequate.
3. Subject area comparison with other published material
- The study should compare more with existing research. It seems to be missing the state of the art section.
4. Methodological Improvements
- For this study to be of greater impact, it would require a comparison between the theoretical results acquired by the simulation, with practical, in-field results. Numerous times a paper claims that they have reinvented the wheel but only through simulations. Practical experimentations often reject that claim. It is suggested that the authors create a practical testbed and run real life scenarios so they can have some hard evidence on their claims.
5. Consistency of Conclusions with Evidence
- Conclusions are short and to the point.
6. Appropriateness of References
- It is necessary to add the references of the studies that will be added in the state of the art section when a comparison with existing systems will be made.
7. Comments on Tables and Figures
- Some of the maths used, although analytical, might be shortened as the reading gets disrupted, (i.e. p.7)
Author Response
First, I would like to sincerely thank you for your detailed and thoughtful review. Below, I provide my responses to your comments.
Comment 1: Main question addressed by the research
The research question is set but not explicitly: can a sequence design (like a priority driven rendezvous system in a frequency hopping sequence) be used to increase efficiency in cognitive radio? This should be better emphasised. There are also 3 objectives laid out clearly
Response 1:
The channel searching pattern for rendezvous proposed by Paul, Choi, Jang, and Kim demonstrates the best performance among currently available patterns. Based on this, we believe that allowing users with higher priority to establish communication first in the CR environment can potentially enhance the overall efficiency of the cognitive radio system.
Comment 2: Originality and Relevance to the Field
As cognitive radio is a fascinating subject, any improvement in the priority algorithm is of major importance. The study does make clear the necessity of this but fails to prove why the competing systems are inadequate.
Response 2:
I do not consider competing systems to be inadequate. Rather, while previous priority-based systems have typically relied on adjusting frequency allocation or implementing measures at the MAC layer, the newly proposed scheme differentiates priority by applying a new channel searching pattern exclusively to secondary CR users, without altering other system components. This approach has not been attempted before, and because it does not modify the rest of the system, there is significant potential to further enhance performance by additionally incorporating conventional methods such as differentiated frequency allocation or MAC-layer measures. I would like to clarify once again that the existing approaches are not problematic; instead, I hope that our work may be seen as offering antoher direction.
Comment 3: Subject area comparison with other published material
The study should compare more with existing research. It seems to be missing the state of the art section.
Response 3:
I have given this matter considerable thought as well. However, as mentioned in my previous response, the scheme we propose is based on the work of Paul, Choi, Jang, and Kim, and to the best of my knowledge, there have been no existing studies that have developed similar research directions using this foundation. While it would be ideal to include comparative results with such works, I believe the approaches are fundamentally different. Instead of claiming superiority over previous methods, I hope you will view our work as presenting a new direction—one that does not modify other system components and can potentially be combined with existing research results.
In addition, since this point was not clearly reflected in the original introduction, we have revised the introduction to better address it.
Comment 4: Methodological Improvements
For this study to be of greater impact, it would require a comparison between the theoretical results acquired by the simulation, with practical, in-field results. Numerous times a paper claims that they have reinvented the wheel but only through simulations. Practical experimentations often reject that claim. It is suggested that the authors create a practical testbed and run real life scenarios so they can have some hard evidence on their claims
Response 4:
I completely agree that building an actual testbed and conducting experiments is the best and most definitive way to validate the performance of a scheme. However, I believe you would also understand that, for individual researchers or small teams, constructing such a testbed is extremely challenging. Because it is difficult to implement in a real testbed, I hope you understand that the best I could do was to conduct theoretical performance analysis and validation through simulations.
Comment 5:Consistency of Conclusions with Evidence
Conclusions are short and to the point
Response 5:
Thank you. If there are any additional points you would like to be included or revised, please let me know and I will be sure to reflect them.
Comment 6: Appropriateness of References
It is necessary to add the references of the studies that will be added in the state of the art section when a comparison with existing systems will be made.
Response 6:
As mentioned earlier, the new scheme is proposed as a different approach from conventional methods, and I hope it will be understood as one that can also incorporate existing techniques. If you are willing to recommend good references, I would be happy to include them.
Comment 7: Comments on Tables and Figures
Some of the maths used, although analytical, might be shortened as the reading gets disrupted,
Response 7:
While reviewing the manuscript to review the number of equations in response to your comment, I was able to identify and correct a minor error in the formulas. I sincerely appreciate your attention to detail. However, since some reviewers request that mathematical sections be described as thoroughly as possible, it may be difficult to reduce them further. I kindly ask for your understanding in this regard.
Reviewer 2 Report
Comments and Suggestions for AuthorsThis paper studies the channel rendezvous of cognitive radio. Generally, the topic is not new that has been comprehensively investigated during the past decades. I have the follow-up comments.
1. What is the main contribution? Priority is not a sufficient contribution.
- Is there any comparison with existing favorite algorithms? I have not found that.
- What is the computational complexity?
- Just based on an existing algorithm is not sufficient. Also, it cannot be directly pointed out in the abstract.
- The description of the main algorithm is not sufficient with only two pages
Author Response
Comment 1: What is the main contribution? Priority is not a sufficient contribution.
Response 1:
Previously, methods for creating differences in rendezvous performance according to priority have primarily focused on adjusting allocated frequencies or making modifications at the MAC layer. I believe this is partly due to the fact that prior research on channel searching patterns for rendezvous has mainly been based on random number or simple prime number approaches, rather than mathematical analyses such as those using finite fields. In this study, without modifying other parts of the system, we classify CR users into two groups—primary and secondary—and propose a method that assigns distinct p-ary sequences with different periods as channel searching patterns for rendezvous, thereby creating performance differences based on user priority. Because the newly proposed scheme does not modify other system components, it is highly likely that it can achieve even better results by also adopting existing research methods. Therefore, I believe the contributions of this paper are threefold: (1) proposing a method to create performance differences in rendezvous by assigning different channel searching patterns according to CR user priority, (2) presenting a new approach that differs from conventional research directions, thus suggesting a new perspective for this area, and (3) demonstrating that, since the proposed method can be applied without altering other system components, it is possible to find opportunities for improved performance by combining it with previous studies.
Comment 2: Is there any comparison with existing favorite algorithms? I have not found that.
Response 2:
The reviewer is correct in pointing out that a comparison with existing methods is not included. The reason is as follows. While previous priority-based systems have typically relied on adjusting frequency allocation or implementing measures at the MAC layer, the newly proposed approach differentiates priority by applying a new channel searching pattern exclusively to secondary CR users, without modifying other system components. This is a direction that has not been previously attempted, and since it does not require changes to other system elements, it could potentially offer further performance enhancements by incorporating existing methods, such as differentiated frequency allocation or MAC-layer interventions. To clarify, I am not suggesting that existing approaches are problematic; rather, I hope our work will be seen as introducing a new perspective.
Comment 3: What is the computational complexity?
Response 3:
When I mention that resource allocation or adjustments in the MAC layer increase system complexity, I mean that in such cases, additional functionalities must be incorporated into the system to support both primary CR users and secondary CR users. In the newly proposed method, as shown in the revised Figure 1, the only change is that the secondary CR user uses a different pattern for rendezvous; there are no modifications required on the part of the connecting counterpart. Therefore, compared to other methods, the proposed approach involves fewer changes to the system. If you have any suggestions for expressing this point more appropriately, I would be pleased to reflect them.
Comment 4: Just based on an existing algorithm is not sufficient. Also, it cannot be directly pointed out in the abstract.
Response 4:
In accordance with the reviewer's comments, I have described this content more thoroughly in the manuscript.
Comment 5: The description of the main algorithm is not sufficient with only two pages
Reponse 5:
In response to the reviewer's comments, I have revised and supplemented the relevant section. If you have any further suggestions or recommendations for improvements, I will be glad to incorporate them.
Reviewer 3 Report
Comments and Suggestions for AuthorsThis paper introduces a priority-based channel-hopping scheme using distinct p-ary m-sequences. The reviewer agrees that the idea is promising; however, in their viewpoint, the following comments should be carefully addressed before the paper can be considered for publication.
C[1]: The authors mention that the sequence-based priority differentiation "has remained largely unexplored" and portray existing work as mostly channel-allocation or MAC-based. The reviewer suggests that it would strengthen the paper to compare the introduced scheme with any existing sequence-design-based prioritization, if any exists, or explicitly state that no such work is known and why. Even if no such schemes are discussed in the literature, the authors should include a related work section with a similar approach, highlighting differences and novelties vis-à-vis their contribution.
C[2]: The system architecture description (Figure 1) is rather brief. The reviewer suggests that key assumptions should be clearly stated, potentially, in a "System Model" subsection. For instance, are PUs LUs licensed in the usual CR sense, or just high-priority CR users? As the reviewer understands, the abstract and introduction mix "Licensed users (LUs)" and "Primary users (PUs)" and then treat PUs as users that use the primary sequence. This might be short of confusing for readers.
C[3]: As the reviewer comprehends, the mathematical exposition around the finite field and trace function definitions contains some inconsistencies. For example, "α" is sometimes defined as a primitive element of Fp4 and elsewhere as belonging to Fp2. The reviewer recommends that the authors carefully revisit and verify the field assignment for each primitive element (α, β) and clearly specify which field corresponds to which user sequence.
C[4]: In the derivation of Theorem 3 (ETTR for the secondary user), the reviewer recommends that the authors include a toy numerical example or table (for instance, with p=19) to illustrate how closely the truncated geometric sum approximates the exact ETTR. This would clarify the validity of the assumption that certain terms "become negligible for large p".
C[5]: The authors should provide more information about the simulation methodology in Section 4 so that the numerical results can be reproducible.
C[6]: An additional round of proofreading is required. The reviewer was able to identify numerous typographical and formatting errors (e.g., occures, primariy)
Author Response
Comment 1:
The authors mention that the sequence-based priority differentiation "has remained largely unexplored" and portray existing work as mostly channel-allocation or MAC-based. The reviewer suggests that it would strengthen the paper to compare the introduced scheme with any existing sequence-design-based prioritization, if any exists, or explicitly state that no such work is known and why. Even if no such schemes are discussed in the literature, the authors should include a related work section with a similar approach, highlighting differences and novelties vis-à-vis their contribution.
Response 1:
As far as I have found, there have not been any previous approaches that differentiate performance by applying different channel searching patterns according to priority. I believe this is because most existing methods have mainly relied on random number or prime number-based approaches rather than mathematical constructions. Furthermore, the results of existing studies on channel searching patterns for rendezvous show significant performance gaps and possess different mathematical structures compared to the work of Paul, Choi, Jang, and Kim on which this paper is based, making direct comparison quite challenging. If you are aware of any related research that has been published, please let me know, and I will make sure to incorporate it into the manuscript.
Comment 2: The system architecture description (Figure 1) is rather brief. The reviewer suggests that key assumptions should be clearly stated, potentially, in a "System Model" subsection. For instance, are PUs LUs licensed in the usual CR sense, or just high-priority CR users? As the reviewer understands, the abstract and introduction mix "Licensed users (LUs)" and "Primary users (PUs)" and then treat PUs as users that use the primary sequence. This might be short of confusing for readers.
Response 2:
I appreciate your insightful comments. Thank you very much. To avoid confusion, I have redefined the users as primary CR users and secondary CR users according to their priority, and have reflected this terminology in Figure 1 and throughout the manuscript.
Comment 3: As the reviewer comprehends, the mathematical exposition around the finite field and trace function definitions contains some inconsistencies. For example, "α" is sometimes defined as a primitive element of Fp4 and elsewhere as belonging to Fp2​. The reviewer recommends that the authors carefully revisit and verify the field assignment for each primitive element (α, β) and clearly specify which field corresponds to which user sequence.
Response 3:
I was unable to find any section where \alpha is used as a primitive element of F_{p^2}. However, there appears to be a similar case in Theorem 2, specifically in the definition of the nonbinary Kasami sequence where tr_1^2(\alpha^{Tt} is used. In this case, since \alpha^{tT}=\beta^t, there doesn't seem to be any mathematical issue. Do you think it would be better to revise the part in the preliminaries where \alpha is introduced as a primitive element of F_{p^n}? Or is there a section I might have missed? If you let me know, I will make the necessary changes.
Comment 4: In the derivation of Theorem 3 (ETTR for the secondary user), the reviewer recommends that the authors include a toy numerical example or table (for instance, with p=19) to illustrate how closely the truncated geometric sum approximates the exact ETTR. This would clarify the validity of the assumption that certain terms "become negligible for large p".
Response 4:
I have summarized and included the values corresponding to each p in Table 1.
Comment 5: The authors should provide more information about the simulation methodology in Section 4 so that the numerical results can be reproducible.
Response 5:
In accordance with the reviewer's suggestion, I have added detailed information regarding the computer specifications, programming language, and compiler.
Comment 6: An additional round of proofreading is required. The reviewer was able to identify numerous typographical and formatting errors (e.g., occures, primariy)
Response 6:
I have carefully corrected the typographical errors through additional proofreading. Thank you very much for your valuable suggestion
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsThank you for your reply. i can see that in the text you have made some changes reflecting my comments. however, many times it seems that you have chosen to keep the work as is as it would otherwise involve a lot of additional work.
i would urge you in future versions to experiment and compare the theoretical with the practical results.
Author Response
Comment 1:
Thank you for your reply. i can see that in the text you have made some changes reflecting my comments. however, many times it seems that you have chosen to keep the work as is as it would otherwise involve a lot of additional work.
i would urge you in future versions to experiment and compare the theoretical with the practical results.
Response 1:
Thank you very much for your suggestions regarding future research. In line with your comments, we have added a discussion of related prior work to the Introduction. If there are any additional references or points you would like us to incorporate, we would be pleased to include them in the revised manuscript.
Reviewer 3 Report
Comments and Suggestions for AuthorsThe reviewer thanks the authors for carefully addressing the comments. Overall, the manuscript has been significantly improved and, in the reviewer's eyes, the manuscript can now be deemed suitable for publication at the Applied Sciences journal. A last minor comment regards the initial C[3]. Specifically:
The reviewer thanks the authors for re-examining their manuscript and mathematics regarding C[3]. To explain the original comment's intention: the mathematics itself appears correct; the reviewer's initial comment was aimed purely at notational clarity. That is, in Theorem 2, the expression
\[
\operatorname{tr}_{1}^{2}\!\left(\alpha^{T t}\right)
\]
may give the impression that $\alpha \in \mathbb{F}_{p^{2}}$ unless the relationship between
\[
\alpha \in \mathbb{F}_{p^{4}}
\qquad\text{and}\qquad
\beta = \alpha^{T} \in \mathbb{F}_{p^{2}}
\]
is stated explicitly. Thus, the reviewer recommends adding a brief clarification to make the field assignments of the primitive elements unambiguous for the reader.
Author Response
Comment 1:
To explain the original comment's intention: the mathematics itself appears correct; the reviewer's initial comment was aimed purely at notational clarity. That is, in Theorem 2, the expression
\[
\operatorname{tr}_{1}^{2}\!\left(\alpha^{T t}\right)
\]
may give the impression that $\alpha \in \mathbb{F}_{p^{2}}$ unless the relationship between
\[
\alpha \in \mathbb{F}_{p^{4}}
\qquad\text{and}\qquad
\beta = \alpha^{T} \in \mathbb{F}_{p^{2}}
\]
is stated explicitly. Thus, the reviewer recommends adding a brief clarification to make the field assignments of the primitive elements unambiguous for the reader.
Response 1:
Thank you for your helpful suggestions. I have reflected the reviewer’s comments in the manuscript as follows. First, on page 4, I revised the field extension description to $\beta=\alpha^{(p^n-1)/(p^k-1)}$ to strengthen the earlier explanation. In addition, I modified the corresponding part of Theorem 2 to $\mbox{tr}_1^2(\beta^{t+i})$ and added the clarification “where $\beta=\alpha^T$ is a primitive element of $F_{p^2}$” below.
