Propagation Modeling of Unmanned Aerial Vehicle (UAV) 5G Wireless Networks in Rural Mountainous Regions Using Ray Tracing

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This paper presents a Propagation Modeling of UAV Wireless Networks in Rural Mountainous Regions using Ray Tracing

What is the maximum battery charge duration of the UAV.

Do a comment if making a network of 2 or more UAVs improves the performance of the communications system.

Comments on the Quality of English Language

Revise the English grammar. In the text avoid usung the first person "we".

Author Response

Reviewer 1 has two comments on how to improve our manuscript. We are thankful for them. Below are our responses and efforts to address them. We have also improved the "front" of the paper in terms of supporting figures, tables and equation, and also the English language aspect.

Reviewer 1, Comment 2 

What is the maximum battery charge duration of the UAV? 

Response: 

Thank you for your insightful question regarding the maximum battery charge duration of the UAV. The Sub-section 3.1, System Model (below Table 3) elaboration has been updated to address this point as follows: 

“UAVs are often fueled by high-energy lithium batteries, with flight periods ranging from 20 to 40 minutes. The battery charge duration is influenced by multiple factors, including the consumption of other onboard electronics and the power level of transmission, particularly when the UAV functions as a base station [ref]. Factors such as signal strength, interference, and the need for signal re-transmissions in certain channel models can all contribute to increased battery usage. UAVs may need to adjust their communication protocols, flight paths, or transmission power to optimize battery consumption. The resulting model can contribute to the automatic adjustment and power consumption optimization strategies but is not within the scope of this study.” 

 

Reviewer 1, Comment 2 

Do a comment if making a network of 2 or more UAVs improves the performance of the communications system. 

Response: 

Thank you for pointing out this concern. This constraint is added in the manuscript in Section (4.4) paragraph 1. 

“This paper primarily focuses on the deployment of UAVs in specific environmental settings, and while it acknowledges the importance of weather impacts on UAV performance, a detailed analysis of these factors is beyond the current scope. The impact of weather that was considered is rain and gas, but not fog, humidity, wind, and temperature variations. Lower frequencies of 3.5 GHz and 6 GHz are generally less affected by weather conditions compared to higher frequencies 28 GHz and 60 GHz, which suffer significant attenuation due to these factors. At lower altitudes 30 m, UAVs are less exposed to severe weather but are more likely to encounter ground-level obstacles, while higher altitudes 75 m and 120 m offer larger coverage areas but increase exposure to atmospheric conditions such as strong winds and temperature variations, leading to greater signal degradation. Therefore, higher frequencies and altitudes necessitate advanced adaptive techniques to mitigate weather-related impacts on UAV communications. Future work will include a detailed analysis and quantification of weather effects to provide a more comprehensive understanding of UAV performance under varying conditions.”  

Reviewer 2 Report

Comments and Suggestions for Authors

1- The proposed paradigm is primarily based on theoretical models and lacks sufficient real-world testing.

2-It's possible that the suggested model's conclusions won't apply to different types of terrain or metropolitan environments.

3- The impacts of weather on UAV performance are not fully examined in this paper.

4- The link between signal strength and frequency is not thoroughly investigated.

5- The suggested approach ignores in-depth causes or variations in favour of concentrating on fundamental delay measures.

6- Omitting practical methods for monitoring and adjusting in real time.

7- The types and sources of interference are not thoroughly examined in the suggested paradigm.

8- Comprehensive guidelines for certain UAV uses are lacking.

9- The suggested concept makes no mention of operational expenses, regulatory restrictions, or viability.

10- It is possible that there are long-term patterns and variances in signal propagation that cannot be fully understood from the study data. 

Author Response

Reviewer 2 made ten comments on how to improve our manuscript, and we are thankful for them. Below are our responses and efforts to address them. We have also improved the "front" of the paper in terms of supporting figures, tables, and equations, and the English language aspect.

 

Reviewer 2, Comment 1 

The proposed paradigm is primarily based on theoretical models and lacks sufficient real-world testing. 

Response: 

 

Thank you for the feedback. The manuscript is updated to mention the following justification in Sub-section 3.1 in paragraph 2. 

“Although this study is primarily based on simulations, it incorporates real-world information using OpenStreetMap (OSM) files, which accurately depict the landscape, terrain, and obstacles such as buildings and vegetation in the chosen environment. These details are crucial for the propagation modeling, as they impact the signal behaviour and path loss characteristics. The frequency operations adhere to established standards, ensuring the practical relevance of the simulations. This foundational understanding paves the way for future real-world measurements, which can be conducted more efficiently and resourcefully, guided by the insights gained from these simulations.” 

 

Reviewer 2, Comment 2: 

It's possible that the suggested model's conclusions won't apply to different types of terrain or metropolitan environments. 

Response: 

Thank you for the concern. The manuscript is updated in conclusion to address this comment. 

“The final suggested models are particularly relevant to the specific types of environments discussed in this study, such as mountainous and suburban areas. These conclusions provide a realistic representation of performance in near real-world scenarios, offering valuable insights for drone operators in such environments. For different types of terrain or metropolitan settings, further investigation using the same framework is required due to differences in obstacles and vegetation. However, the performance trends, especially those influenced by distance-dependent path loss, are expected to be similar. While the average RSS may vary, the model presented here can still provide useful trends and insights that can be adapted to other environments with additional validation.”. 

 

Reviewer 2, Comment 3: 

The impacts of weather on UAV performance are not fully examined in this paper. 

Response: 

Thank you for the feedback. The manuscript has been updated to include more description about the potential effects of concrete buildings, weather, and foliage on RSS to users in Sub-section 3.2.1 which is a motivation to our study. The subsection also explains how it was done. 

“The higher the altitude of the UAV, the greater the distance between the UAV  and ground users, resulting in an increase in free space path loss.  Furthermore, in a realistic environment, the building material and the presence of weather and foliage affect the received signal strength. Therefore, this study includes the effect of concrete, weather, and foliage in calculating received signal strength at the user end. The RT propagation model used in Matlab determines the path loss of each ray using electromagnetic analysis. This calculation includes free-space, reflection, and diffraction losses according to the characteristics of building materials such as concrete, provided in the ITU standards [ref] and [ref] For the consideration of losses due to weather, this study calculates the attenuation due to the presence of rain and atmospheric gases as per ITU standards [ref] and [ref]. The signal strength is also affected by the presence of foliage. Since we have chosen 5 m depth, then Weissberger_b model [ref] is used to include the losses due to foliage in this study.” 
 

Reviewer 2, Comment 4: 

The link between signal strength and frequency is not thoroughly investigated. 

Response: 

Thank you for your constructive feedback. We have expanded our investigation on the link between signal strength and frequency in the attached revised document, throughout Sub-section 4.1 and 4.2. But one particular paragraph can be shared here as follow, 

“Table 4 and Table 5 illustrate how average RSS in (dBm) varies across different frequencies 3.5 GHz, 6 GHz, 28 GHz, and 60 GHz and heights 30 m, 75 m, and 120 m, but this time with the sequential introduction of concrete for building and the cold mountains, weather and foliage depth for the green parts of the mountains. Higher frequencies generally experience more significant attenuation, resulting in lower signal strengths compared to lower frequencies. Specifically, at 60 GHz, the dBm values are more negative than at 3.5 GHz and 6 GHz across all elevations. Increased elevation typically improves LOS conditions, leading to better coverage and service capacity. However, this advantage diminishes at higher frequencies due to heightened susceptibility to environmental factors such as atmospheric absorption, reflection, and diffraction. At higher altitudes, transmissions with higher frequencies deteriorate more quickly. Signal strength exhibits greater variability at higher frequencies, primarily due to factors like weather conditions, vegetation, and physical obstacles” 

Reviewer 2, Comment 5: 

The suggested approach ignores in-depth causes or variations in favour of concentrating on fundamental delay measures. 

Response: 

Thank you for your valuable feedback.  

In the presented cases, concentrating on basic delay measurements (max, min, and average delays) at various altitudes provides a better understanding of the effect of height on signal transmission without diving into specific causes or variations. This method demonstrates that, regardless of the setting S1 and S2, delay values rise modestly with height. In mountainous locations, the average delay is reasonably steady (about 2.09 to 2.11 µs) throughout elevations, but in suburban areas, the average delay is somewhat greater and increases more noticeably (from 2.55 to 2.83 µs) with height. By focusing on these core parameters, the research is clearer and exposes major patterns in delay behaviour across various settings and altitudes. 

Note: This paragraph is not included in paper because the delays are already analysis in the section and all of the explanation has been revised. 

 

Reviewer 2, Comment 6: 

Omitting practical methods for monitoring and adjusting in real time. 

Response: 

Thank you for your insightful feedback, however we are not sure to have understood the comment. The following respond is given in Section 4.3 with the hope to do the feedback justice. The paragraph is above Table 7 and Table 8. 

“While this study focuses on simulation-based analysis without practical methods for real-time monitoring and adjustment, it is essential to note that simulations based on probabilistic models can effectively capture real-time behaviours in dynamic environments. Implementing continuous real-time adjustments could indeed enhance communication performance by improving accuracy, but it would also demand substantial processing resources. For practical UAV deployments, predictive modelling derived from simulations plays a crucial role in optimizing operations and mitigating risks. Future advancements in artificial intelligence hold promise for enabling real-time adaptive strategies in UAV deployment scenarios. However, the current study lays a foundational understanding through simulation-based probabilistic modelling, which is instrumental in informing initial deployment strategies and guiding future research towards more adaptive and efficient UAV communication systems.” 

 

Reviewer 2, Comment 7: 

The types and sources of interference are not thoroughly examined in the suggested paradigm. 

Response: 

The types and sources of interference are critical aspects that require further investigation beyond the scope of this study. This aspect is discussed in the new subsection 4.4 o future works and consideration beyond current scope. 

“While our research focuses on evaluating UAV applications in emergency scenarios using ray tracing propagation modeling, understanding interference sources is essential for comprehensive system analysis. It's important to note that the current findings, which do not account for interference, may represent an upper bound of performance. When interference is considered, the signal-to-noise and interference ratio impacts signal quality for all users, although trends at different altitudes are likely to follow similar patterns. Future studies should explore co-channel and adjacent channel interference to better understand their effects and represent a more practical limitation of the propagation environment.” 

 

Reviewer 2, Comment 8: 

Comprehensive guidelines for certain UAV uses are lacking. 

Response: 

Thank you for this suggestion. But we believe the guidelines are not relevant to be included in this paper as the propagation modeling is a generic approach to consider the transmitter and transmission strategy for a UAV communication. It can be applied to any UAV regardless of its type. 

 

Reviewer 2, Comment 9: 

The suggested concept makes no mention of operational expenses, regulatory restrictions, or viability. 

Response: 

Thank you for this suggestion. But we believe the proposed aspects are not relevant to be included in this paper as the propagation modeling is a generic approach to consider the transmitter and transmission strategy for a UAV communication. It can be applied to any UAV regardless of its type. However, the specific regulatory concern of maximum flying height is indeed important and has been considered in the study. To address this concern, we have modified the title for Sub-section 3.25 to “Range for height optimization” and has improved its elaboration to include sources of height limits. 

“The determination of optimal height for UAV as BS is restricted to regulatory limitations [refs]. Some countries allow UAVs to fly up to 200 m, but in general, most countries agree to ensure that UAVs stay below 120 m to help maintain a restricted altitude range, which minimizes the chances of accidents with commercial and private manned aircraft that usually fly at higher altitudes. This measure enhances air traffic safety. UAV operators should follow national aviation rules. Exceeding the designated altitude of 120 m without explicit authorization might result in legal ramifications and provide potential hazards to safety. Special licenses for higher altitude operations may be given but must undergo stringent safety evaluations and collaboration with aviation authorities.” 

Reviewer 2, Comment 10: 

It is possible that there are long-term patterns and variances in signal propagation that cannot be fully understood from the study data.  

Response: 

Thank you for this feedback. This aspect is discussed in paragraph 3 of the new subsection 4.4 of future works and consideration beyond current scope. 

“The work herein provides valuable insights into the immediate effects of UAV communication in emergency scenarios using ray tracing propagation modelling. It's important to acknowledge that long-term variations in signal propagation dynamics, such as seasonal changes, evolving environmental conditions, operational fluctuations, and new developments like buildings, can significantly impact real-world performance over time. Similarly, changes in vegetation can alter foliage losses, further influencing propagation characteristics. Future studies could benefit from analyzing these factors across various temporal and environmental conditions to provide a more comprehensive understanding of UAV communication system reliability and performance stability. This approach is crucial, especially when new developments and environmental changes require further experimentation to validate and refine the model.” 

Author Response File: Author Response.docx

Reviewer 3 Report

Comments and Suggestions for Authors

This paper comprehensively investigates the signal propagation and performance under multiple frequencies, from midband to mmWaves range. The analysis considers critical parameters such as path loss, received power, weather loss, foliage loss, and the impact of varying UAV heights.

Some considerations regarding the content of the paper:

- The Literature Review of current research on this topic is not so modern. There are only several publications after 2020 that reflect the state of research in this area nowadays.

- It would be good to provide the decoding of abbreviations. For example, RT.

- It is better to provide an explanation of the variables with the word "where" after each formula.

- The flowchart of modeling path loss in Matlab using the two scenarios in figure 4 should be given more detailed.

- There is no information on how were get values for table 3.

- Figures 5, 6 and tables 6, 7 are located outside the text fields.

- There is much space before tables 2, 3 and after figure 5. It is better given text, which situated after table 2, 3 and figure 6 in accordence.

- The text in figures 5, 6 is too small and it is difficult to consider it.

- Very weak conclusion about experiments of work. It is better giving some analysis of obtained results.

- The text of paper should be carefully read and corrected errors in text formatting. For example, there is no space in “the sea[1,2]”, some names of table have points in the end.

- References are not designed clearly according to the requirements of the journal, for example, reference10, there is no on information about year of reference.

Comments on the Quality of English Language

Authors should carefully examine and correct syntactic errors.

Author Response

Reviewer 3 has provided us with 11 insightful comments. Below are the elaboration to our efforts in fulfilling them.

Reviewer 3, Comment 1:

The Literature Review of current research on this topic is not so modern. There are only several publications after 2020 that reflect the state of research in this area nowadays.

Response:

Thank you for your concern. The manuscript has been updated with two more recent and relevant literature review, as reflected in the new Table 2 and references [54, 55].

Reviewer 3, Comment 2:

It would be good to provide the decoding of abbreviations. For example, RT.

 

Response:

Thank you for your helpful suggestion. We have revised the whole decoding of abbreviations, including RT, in the attached revised document. A list of abbreviation following MDPI template is also provided at the end of the manuscript.

Reviewer 3, Comment 3:

It is better to provide an explanation of the variables with the word "where" after each formula.

Response:

Thank you for your suggestion. We have now included explanations of the variables using the word "where" after each formula in the attached revised document.

Reviewer 3, Comment 4:

The flowchart of modeling path loss in MATLAB using the two scenarios in figure 4 should be given more detailed.

Response:

Thank you for your feedback. We have provided a more detailed flowchart of modeling path loss in MATLAB using the two scenarios in Figure 4 in the attached revised document.

Reviewer 3, Comment 5:

There is no information on how where get values for table 3.

Response:

Thank you for your feedback. We have updated the paragraph in the Sub-section 3.1, System Model and with references 57 and 58 to provide information of how we obtained the sensitivity values for Table 3. The Table 3 of simulation parameters has also seens improvement.

Reviewer 3, Comment 6:

Figures 5, 6 and tables 6, 7 are located outside the text fields.

 

Response:

Thank you for your comment. We appreciate your suggestion regarding the placement of large figures and tables. However, we have verified, as per the MDPI format, we are allowed to place Figures 5, 6, and Tables 6, 7 outside of the text fields due to their large size and for clarity purposes. Table 6 and 7 has been improved to support our analysis and the size is now smaller.

Reviewer 3, Comment 7:

There is much space before tables 2, 3 and after figure 5. It is better to give text, which is situated after table 2, 3 and figure 6 in accordance.

Response:

Thank you for your observation. We have adjusted the layout to reduce the space before Tables 2 and 3 and after Figure 5, and we have rearranged the text following Table 2, Table 3, and Figure 6 accordingly in the revised document. The paper was written under Latex, some spaces cannot be modified due to the properties of the template. We believe the final editor will help us in this aspect once the paper is accepted.

Reviewer 3, Comment 8:

The text in figures 5, 6 is too small and it is difficult to consider it.

Response:

Thank you for your observation. We agree and we have generated new Figures with bigger legends and hope to have solved the issues. However, due to comparing 4 images together, the improvement is still limited.

Reviewer 3, Comment 9:

Very weak conclusion about experiments of work. It is better to give some analysis of obtained results.

Response:

Thank you for your feedback. We have strengthened the conclusion by providing extra analysis of the obtained results from the experiments as follows.

 

“For the frequency of 3.5 GHz, for example, the average losses in received power for weather, foliage, delay, and phase shift are below 1.5 dBm, 3 dBm, 2μs, and 3 degrees, respectively. In the height variation analysis, flying a UAV at a height of 75 m results in optimized conditions that maximize LOS conditions and minimize NLOS complete outage of no signal”

Reviewer 3, Comment 10:

The text of paper should be carefully read and errors in text formatting corrected. For example, there is no space in “the sea[1,2]”, some names of table have points in the end.

Response:

Thank you for your feedback. We have carefully reviewed the text for formatting errors, such as missing spaces and inconsistent table naming conventions, and resolved all issues highlighted in red in the revised document.

Reviewer 3, Comment 11:

References are not designed clearly according to the requirements of the journal, for example, reference10, there is no information about year of reference.

Response:

Thank you for your feedback. We have revised the references to meet the journal's requirements and ensured that all references, including reference 10, now include complete information, such as the year of publication, in the attached revised document.

 

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

The authors have addressed all the required comments.