Resource and Trajectory Optimization in RIS-Assisted Cognitive UAV Networks with Multiple Users Under Malicious Eavesdropping

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The introduction provides a solid background and clearly defines the research problem. However, it lacks a detailed discussion of recent studies on the application of RIS in UAV networks, particularly in the context of secure communications. Consider including references to key works published in the past 2–3 years to better position the research within the current state of the field. In the section describing the system model (lines 151–243), equations (1)–(3) define the UAV trajectory constraints, such as maximum speed and altitude. However, it would be helpful to clarify how these assumptions align with real-world UAV flight regulations, particularly in urban environments. Additionally, equation (3), which describes the phase shift range of RIS, could benefit from an explanation of how phase variations affect transmission quality under NLoS interference conditions.

Section 3 describes the BCD-SCA algorithm for solving the optimization problem iteratively. For example, in lines 254–260, the optimization of the RIS phase is discussed. A more detailed explanation of why this method is effective and how it ensures convergence would strengthen this part. In equation (28), the authors introduce auxiliary variables x(n) and y(n). It would be useful to elaborate on how these variables simplify the problem and contribute to computational efficiency.

The simulation results presented in Section 4 are clearly laid out, but a few improvements could enhance clarity. For instance, in Figure 2, more detailed descriptions of the axes and legend would make it easier to interpret the increase in "secure bits" as a function of the number of RIS elements (K). Similarly, the discussion of Figure 4 (lines 373–380) could be expanded to explain why performance increases linearly with the number of RIS elements. In Figure 6 (lines 394–405), the UAV-C trajectory under different scenarios should be explained in more detail, particularly in relation to the impact of eavesdropper interference.

The conclusions summarize the main contributions effectively. However, it would be beneficial to discuss potential limitations of the proposed method, such as its scalability in scenarios involving multiple eavesdroppers or dynamic NLoS environments. Additionally, suggestions for future research directions, such as the application of advanced optimization techniques or real-time analysis, could enrich this section.

The citations are generally appropriate and relevant. However, the introduction could be enhanced by including additional references to recent studies from the past 2–3 years, especially those focusing on the integration of UAV and RIS in IoT environments. Adding such references would help to better contextualize the study in the current research landscape.

Author Response

Dear Reviewer, Hope this email finds you well. We would like to express our sincere gratitude for your meticulous review and valuable comments on our manuscript. We have carefully revised the original manuscript according to your suggestions. The revised version has been submitted, and we have also attached a detailed response to your comments (Response to Reviewers) as an attachment for your reference. In the response, we have addressed each of your comments point by point, explaining the corresponding modifications made in the manuscript. Your insights have been extremely helpful in improving the quality of our work. We sincerely hope that the revised manuscript meets your expectations. If you have any further questions or need additional information, please feel free to let us know. Thank you again for your time and effort. Best regards, Juan Li

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The topic of the article is interesting, but you need to look at the formatting a little and make a few observations before publishing.

You should not neglect the similarity percentage because it has currently reached ~20% from over 30%, please fix this aspect.

• In Section 2.1, ensure that all symbols are clearly defined and consistently used throughout the text. For example, the notation for diagonal RIS phase shift matrix [mkθ(n)][mk​θ(n)] appears in multiple forms (e.g., ΘmΘm​), which might confuse readers. A notation table at the beginning would help.
• While Algorithm 1 is detailed, its complexity analysis could be more thorough. Expand on the impact of parameters.
• MM, NN, L1L1​, and L2L2​ on real-world scenarios. Additionally, consider providing pseudocode or flowcharts to improve the algorithm's clarity.
• Figures 2 through 6 focus on convergence and performance under specific constraints (e.g., transmit power, RIS elements). Extend the evaluation to different UAV-C velocities, time-slot lengths, or CU distributions to generalize results.
• The assumptions regarding the perfect knowledge of channel state information (CSI) and the absence of obstacles for the RIS-UAV link (Section 2.1) seem optimistic. A discussion of practical limitations or techniques to estimate CSI and mitigate LoS obstructions would be beneficial.
• In Section 4, while the proposed method is compared with baseline schemes, the manuscript does not delve deeply into why these schemes perform differently. Include a more detailed analysis of the trade-offs, particularly focusing on RIS phase optimization and UAV trajectory.

Comments on the Quality of English Language

No obs.

Author Response

Dear Reviewer, Hope this email finds you well. We would like to express our sincere gratitude for your meticulous review and valuable comments on our manuscript. We have carefully revised the original manuscript according to your suggestions. The revised version has been submitted, and we have also attached a detailed response to your comments (Response to Reviewers) as an attachment for your reference. In the response, we have addressed each of your comments point by point, explaining the corresponding modifications made in the manuscript. Your insights have been extremely helpful in improving the quality of our work. We sincerely hope that the revised manuscript meets your expectations. If you have any further questions or need additional information, please feel free to let us know. Thank you again for your time and effort. Best regards, Juan Li

Author Response File: Author Response.pdf