Optimized Airspace Structures and Sequencing Method for Urban Logistics Droneport

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This paper is about optimized airspace structures and about a sequencing method for urban logistics droneport. The language of the paper is good in general. However, there are a high number of typos and some grammatical errors. The topic of the paper is interesting and actual; the proposed model can be very useful in future droneport design. However, there are significant issues with the literature review as several important topics or practical examples are missing from it. Considering these, I suggest resubmitting the paper after a major revision, focusing on the textual parts of the paper and on the literature review.

In the following, I have several comments and suggestions to improve the paper for its resubmission.

I have the following comments and suggestions regarding the content of the paper:

• In the abstract, the term “logistics drone delivery” is not the best, as logistics and delivery refer to the same activity here, “logistics applications of drones” or the “use of drones for deliveries” would describe the examined processes better. The same problem occurs in the case of “distribution by logistics drones” in the Introduction. Please review the whole paper regarding such terms and update it everywhere where necessary.
• Some general keywords regarding drones, such as UAV or drone, would be useful.
• When writing about cities from China, it would be useful to add the country after the province as well. When writing about cities from the USA, similarly, adding the state before the country would be helpful for the readers.
• While examining the examples, several significant pilots are missing; it would be useful to review this part and include all the relevant drone pilots, for example, the pilots of Amazon, the operation Manna drones in Ireland and in the USA, the Vans & drones concept of Daimler, or the pilots of DHL (including China, Germany, and Tanzania).
• The Introduction focuses only on the technical issues and the analytic background but doesn’t examine the legal requirements and limitations. Please add some new parts with new references to address this issue, focusing on how the legal limitations are affecting the examined area in different parts of the world, for example, in the EU, in the USA, or in China.
• From the Introduction, I’m missing the drone hive concept; a reference should be added regarding that, as it can be completely relevant to the actual topic.
• The quality of Figure 1 is not perfect; a new version with better resolution should be added. The same problem occurs in Figure 5.
• In “2. Airspace structure design of droneport”, at the different parts of the concept, it would be useful to mention how past solutions and ideas were integrated, with adding their relevant references.
• For the numbered parts in section 2 (like (1), (2), etc.), using the heading 2 style would give the paper a better structure, it would be easier for the readers to follow this part.
• From Figure 1, the virtual waiting block is not presented in the next parts, please add the missing description.
• After the title “3. Design of droneport approach and departure procedures”, please write a short introduction for section 3, before starting subsection 3.1. Please present the main steps in the design process and the purpose of this section.
• In lines 242-243, it can be seen that “the lower drone can be affected by the downwash from the upper drone”. But what about the turbulence or the effects of the wind? Please describe it somewhere in the paper how these factors can affect the operations.
• In subsection 3.3., please describe what kind of emergencies are expected in the case of the presented procedures.
• After the title “4. Hungarian algorithm based approach and departure sequencing method”, please write a short introduction for section 4 before starting subsection 4.1. Please present the main steps and the purpose of this section. Here, a short introduction to the Hungarian method with a reference would be very useful. It would also be important to present here why the Hungarian method was selected.
• The same problem occurs in the case of 4.2. and 4.2.1., please update those parts, too.
• In line 339, the concept of queuing theory should be referred to from the literature.
• After the title “5. Simulation Experiment”, please write a short introduction for section 5, before starting subsection 5.1. Please present the main steps and the purpose of the simulation experiment.
• At the end of subsection 5.1., a comparison in % would be very useful to see the exact difference between the two approaches.
• In the Conclusions section, it would be very important to write a paragraph about how and in what process the developed new methodologies could be used in practice and who will be the users of these new solutions.

Comments on the Quality of English Language

I have the following comments regarding minor mistakes in the paper regarding English and formatting:

• In line 44, instead of “low - altitude”, please write “low-altitude”.
• In line 46, before [3], a space is missing.
• In lines 78, and 78, instead of “They then integrated this design…”, “Then, they integrated this design…” would be the correct one.
• In line 82, there is an unnecessary space before “departure”.
• The lists starting in line 133 and in line 142 should follow the formal requirements of the numbered lists; please update them.
• In the list starting in line 142, after “:”, there should be a capital letter; they are not the start of new sentences.
• In line 189, “landing” should be “Landing” with a capital.
• Instead of “in order to”, “to” is absolutely enough; please update this everywhere where it is necessary (for example, in line 203).
• In line 204, a space is missing before “The take-off corridor”.
• In line 205, “drones” should be “Drones” with a capital.
• In line 209, “in case” should be changed to “in the case”.
• In line 210, “apron. When” should be changed to “apron, when”.
• In the section titles, sometimes capitals are used, but sometimes not (for example, 3.1. and 3.2. are different). Please review all the sections and subsection titles and use a uniform capitalization.
• In line 280, “points. The” should be changed to “points, the”.
• In line 281, “Within” should be changed to “within”.
• In line 294, space is missing after the procedure.
• In lines 292, 294, and 296, the formula numberings are missing; please handle these parts as formulas as well, fitting the related text to the new structure.
• The font type of variables and other parts from the formulas in the text are not consistent; please review these using the format based on the template. Additionally, the font size is not consistent; this should be updated, too.
• In line 298, “respectively; In” should be changed to “respectively; in”.
• In line 300, “respectively; And” should be changed to “respectively; and”.
• In line 305, “detail” should be changed to “detailed”.
• In lines 313-314, “In practical” should be changed to “In practice”.
• In line 321, “missions carried by the drones” should be changed to “missions carried out by the drones”. The same problem occurs in lines 370 and 407.
• In line 324, space is missing after 1).
• The line break in line 337 is not necessary, and if should start with a capital after that.
• In the formulas, instead of “x”, the sign of multiplication should used (“∙”).
• In line 347, the sentence should start with a capital.
• In line 371, “indicators, Following” should be changed to “indicators. Following”.
• In line 374, there is an extra space before “drones”.
• In line 380, “following table” should be changed to “following Table 1”.
• In Table 6, “verbal description” should be changed to “description”.
• In line 398, “the” is missing before “actual”.
• In line 424, “Similar” should be changed to “Similarly”. The same problem occurs in line 435.
• In line 431, “.；”should be changed to “;”.
• In line 446, “flow chart” should be changed to “flowchart”.
• In lines 467 and 468, the spaces before “s” for second are missing in all 3 cases, but after s, there are unnecessary spaces in every case. The same problem occurs in lines 487, 489, 513-515.
• In line 478, “respectively. As” should be changed to “respectively, as”.
• In line 479, “Figure (a)” should be changed to “Figure 8 (a)”, and similarly in the case of (b).
• In line 507, “The setting for drone arrival flow.” is not clear; it is very likely that one or more words are missing from the sentence. Please rewrite the related paragraph to make it clearer.
• The font type for the caption of Figure 9 is not correct; please check this issue.

Author Response

Please refer to the pdf.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Summary of the Paper

The paper proposes an optimized airspace structure and sequencing method to improve the efficiency and safety of urban logistics drone ports, where takeoff and landing are critical bottlenecks. Authors introduce a novel airspace structure that spatially segregates ascending and descending drones, minimizing collision risks and improving throughput. The framework includes dedicated layers for arrivals, departures, holding, emergency situations, and takeoff corridors. Additionally, a real-time sequencing model based on the Hungarian algorithm is developed to optimize the order of drone takeoffs and landings. This model incorporates drone-specific factors such as battery level, mission priority, and waiting time to create a cost matrix for scheduling.

Simulation experiments compare the proposed airspace design and sequencing method against conventional funnel-shaped configurations and FCFS scheduling.  The results indicate that the new airspace structure reduces takeoff and landing time by 34.8%, and the Hungarian algorithm-based sequencing method prioritizes high-value missions while reducing the average waiting time for low-battery drones by 47.3%. Besides, all low-battery drones landed successfully by leveraging sequencing with the proposed algorithm, whereas conventional strategy led to multiple crashes.

 

Specific Comments

1. L39-L50: The general background on logistic drone delivery is lengthy (Wuhan, Shenzhen, Google Wing, etc. examples), with redundant details that do not directly contribute to the study’s focus. Consider summarizing the examples in one or two sentences for conciseness.
2. Chapter2, 3: The drone port structure is well explained. However, the scalability of the airspace model is not explicitly addressed. For example, is there a defined maximum drone capacity for each layer? The holding layer may face congestion and collision risks if air traffic increases. Given recent air collision incidents in the US, it would be helpful to elaborate on the airspace model's robustness and its ability to manage high-density operations.
3. L294: missing space in equation “procedurein” -> “procedure in”.
4. L329: Just a suggestion: Real drone data could be leveraged to develop a more accurate power consumption model. A linear battery consumption model based solely on time and the power coefficient could be an oversimplification. However, it would be helpful to provide justification for using the simpler model
5. 6. For better readability. Please consider adding a legend indicating LHS for approach and RHS for departure
6. Section 5.1. Could you please provide details on the simulation environment for better reproducibility, including the software & hardware setup?
7. L474: Are the experimental parameters (such as arrival intervals) determined empirically? If so, it would be helpful to provide justification for their selection
8. 2: The Hungarian Algorithm has an O(n³) complexity—will the proposed algorithm remain efficient for very large-scale drone operations? Evaluating its computational performance under various air traffic scales would be valuable.
9. 2: General suggestion: It would be more convincing to compare the proposed algorithm with machine learning-based or heuristic scheduling methods to evaluate its relative efficiency and scalability.
10. References: clean up the "[CrossRef]" tags as needed

Comments on the Quality of English Language

There are more language issues in Chapter 1 but much fewer were observed in the rest of the paper. Please review and revise similar issues (if any) throughout the paper as needed.

Here are a few examples in Chapter1

1. Some sentences/phrases are difficult to follow – L39: “Retail scenarios and demands emerging endlessly” is vague to me. Do you mean "growing demand for faster and more flexible retail deliveries"
2. Some sentences are unnecessarily long and may contain redundant phrases, please revise those sentences when possible. For example, L40-41: “are being implemented and applied at an accelerated pace in many regions across the country.” -> “are being rapidly adopted across many regions”
3. Use words that are more appropriate for academic writing. For example, in L132: “several shortcomings” could be replaced by “several limitations”

Author Response

Please refer to the pdf.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Thank you very much for your corrections. They covered all the previous problems, so I suggest accepting the paper in its present form.

Reviewer 2 Report

Comments and Suggestions for Authors

The revised manuscript has addressed my comments, and the authors' responses have provided clear explanations to my questions. Thank you!