Experimental Study on the Propagation Characteristics of LoRa Signals in Maize Fields

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The paper presents the propagation characteristics of 433 MHz LoRa signals in maize fields, focusing on signal attenuation, RSSI, SNR, and packet loss under dense crop conditions. Such an analysis was carried out via field texts, exploiting different locations. In addition, a theoretical model was also discussed. Moreover, experimental data was exploited to find out a fitting curve. On the whole, the paper can be somehow good, but it needs further efforts to prior to its publication. Therefore, my judgement is for major revisions. The list of comments is below.

• References. Some of them are too old (i.e., 1, 3, 4, 13, 14, 15, 16, and 17). Please, consider substituting them with similar contributions published from 2018 on, or alternatively provide reasons to keep them.

• Section 1. In order to enhance the paper readability, I strongly suggest to split this Section into two. The former should only deal with contextualising the paper, presenting the problem to be solved, and listing the paper contributions (this latter element seems to be missing at the moment). The latter should only deal with related works, by clearly presenting them and comparing them with this paper, especially by highlighting similarities and discrepancies. Moreover, the latter Section must clearly state how this work advances the current state-of-the-art about the topic. This latter element, along with the comparison I have just mentioned, seems to be missing at the moment.

• Section 1. The Section misses of a closing paragraph listing the paper structure

• Section 2. In order to provide readers with a broader perspective about the tackled topic, I suggest the Authors to include the following reference [1, 2, 3, 4]. However, I also strongly encourage the Authors to perform additional research.

• Lines 116-130. I deem the Authors forgot to delete the text the the paper template.

• The Authors presented a theoretical model. However, I deem this is not coherent and consisted with the considered application scenario. Therefore, I strongly recommend to present other models. Some instances are: the Weissberger model, the FITU-R model, the ITU-R model, the Cost 235 model, and the LITU-R model.

• Lines 205-207. Please better explain the cultivation technique.

• In many parts of the paper the Authors exploit the unit of measurement mu. Please,

  use only SI units.

• Table 2. Further details must be provided: coding rate, bandwidth, payload length.

 

• All of the experimental results must be presented by showing their distributions (e.g., boxplots). In so doing, the variability of the data will be available. Indeed, if for a given tested setup 50 packets were sent, it is not reasonable that, say, RSSIs remained constant.

• The Authors must also show the experimental data associated to the packet loss.

• Although the Authors presented a theoretical model (which, as far as I am concerned, must be revised according to the previous comment), such a model was not compared with the experimental results. Indeed, while it is beneficial to fit data aiming to find out a fitting curve, a theoretical comparison must be sorted out.

• Line 336. A typesetting error is surely present.

• The presented results must be better justified and discussed, by providing readers

  with a clear explanation. Indeed too ”may”, ”could”, ”should”, etc., are present.

• Section 5. Please, provide hints about future works.

• Section 6. Such a Section must be further developed in order to make it stronger.

• Finally, the Authors must clearly state the limitations of the proposed approach.

 

References

[1] https://www.mdpi.com/1424-8220/24/5/1621

[2] https://ieeexplore.ieee.org/abstract/document/10254173

[3] https://pubs.aip.org/aip/acp/article/1930/1/020009/783581/Impact-of-foliage-on-LoRa-433MHz-propagation-in

[4] https://www.mdpi.com/1424-8220/24/10/3190

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Comments For Electronics-3488341

In this manuscript, there are some significance and novelty as follows.

The study focuses on the propagation characteristics of LoRa signals in cornfields, especially in the 433 MHz band. This frequency band is widely used in Asian countries, and it is of great practical importance to study its application in agricultural IoT. corn, as one of the major food crops in the world, the effect of its growing environment on wireless signal propagation has not been well studied, and this study fills this gap.

It also conducts field experiments under two different geographic and climatic conditions, namely, Wuwei, Gansu Province, and Tongliao, Inner Mongolia, to verify the reliability and applicability of the model. By systematically adjusting the heights of the transmitting and receiving antennas, the effects of different heights on signal quality and propagation distance were investigated, and detailed experimental data and analysis were provided.

The path loss model was constructed by regression analysis and validated in different environments. The model has high prediction accuracy (R² > 0.9), which provides theoretical support for the deployment of agricultural wireless sensor networks. Future research will incorporate machine learning for dynamic modeling to explore the changes in different crop growth stages, and this prospective perspective is of high academic value.

Therefore, there are some potential reasons for acceptance as follows.

The results of the study provide direct guidance for the design and optimization of agricultural IoT systems, especially in high leaf area crop environments such as cornfields. The study provides specific recommendations for antenna height adjustment, which can help improve signal coverage and communication quality.

The experimental data are detailed, covering different antenna heights, different geographic locations and different crop growth stages. The data are analyzed in a scientific way and the results are highly credible, providing a solid foundation for subsequent research.

The study systematically analyzes the propagation characteristics of LoRa signals in cornfields for the first time, filling a gap in the existing literature. By constructing and validating the path loss model, the study lays the foundation for future dynamic modeling and machine learning applications, which is highly innovative.

However, there are still some potential reasons for rejection as follows.

Although the study conducted experiments in two different geographic locations, the sample size and geographic diversity are still limited. Applicability to other climatic conditions and geographic settings has not been validated, which may affect the generalizability of the results.

Despite the good fit of the path loss model, the model is relatively simple and fails to adequately take into account complex environmental factors such as multipath effects, reflection and refraction. Future studies need to introduce more complex models to improve prediction accuracy.

The study mainly focused on the high-density growth period of maize and lacked long-term monitoring data for other growth stages. Environmental changes at different growth stages may have significant effects on signal propagation and require further research.

As conclusion, this reviewer thinks the manuscript revised according to following suggestions.

1. It is recommended that experiments be conducted under more different climatic conditions and geographic environments to verify the generalizability and reliability of the model. Increasing the number and diversity of samples will help improve the representativeness of the research results.
2. Future studies can introduce more complex propagation models that take into account multipath effects, reflection, refraction, etc. to improve the prediction accuracy of the models. At the same time, combining machine learning algorithms to explore nonlinear relationships and complex environmental effects.
3. Long-term signal propagation monitoring is recommended, covering different crop growth stages. Through dynamic modeling, the effects of time and environmental changes on signal propagation are analyzed to further improve the accuracy and applicability of the model.
4. Figure 7 is expressed nonprofessional.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The paper notably improved after its revision. However, it seems that the Authors did not address at all one of my previous comments, which I copy-paste below for the sake of convenience. Therefore, my judgement stays the same.

• All of the experimental results must be presented by showing their distributions (e.g., boxplots). In so doing, the variability of the data will be available. Indeed, if for a given tested setup 50 packets were sent, it is not reasonable that, say, RSSIs remained constant.

Author Response

Comment 1：

• All of the experimental results must be presented by showing their distributions (e.g., boxplots). In so doing, the variability of the data will be available. Indeed, if for a given tested setup 50 packets were sent, it is not reasonable that, say, RSSIs remained constant.

Response1:

Thank you for pointing this out.We have added the box plots of RSSI under different antenna heights on the page of 8 and 9

Reviewer 2 Report

Comments and Suggestions for Authors

Review Report for "Experimental Study on the Propagation Characteristics of LoRa Signals in Maize Fields"(ID: electronics-3488341-peer-review-v2)

General Assessment

The manuscript presents a comprehensive experimental study on the propagation characteristics of LoRa signals in maize fields, focusing on the 433 MHz frequency band. The research is well-structured, methodologically sound, and addresses a relevant gap in the literature regarding empirical path loss models for agricultural IoT applications. The study’s findings are supported by rigorous field experiments and validation across multiple geographic locations, enhancing the reliability and applicability of the proposed models. 

Strengths

1. Novelty and Relevance: The study provides valuable insights into LoRa signal propagation in dense maize fields, a scenario underexplored in existing literature. The focus on antenna height optimization and path loss modeling is highly relevant for agricultural IoT deployments.
2. Methodological Rigor: The experimental design is robust, incorporating diverse antenna heights, environmental conditions (Gansu, Inner Mongolia, Xinjiang), and validation tests. The use of regression analysis for model fitting and validation demonstrates scientific rigor.
3. Practical Implications: The developed path loss models (e.g., Free Space Path Loss with high R² > 0.9) offer practical guidance for deploying wireless sensor networks in agriculture, balancing signal coverage and cost efficiency.
4. Comprehensive Analysis: The manuscript thoroughly examines key metrics (RSSI, SNR, packet loss) and their dependence on antenna height, supported by clear visualizations (e.g., 3D plots, comparative curves).

Weaknesses and Suggestions for Improvement 

1. Limited Generalizability:

   - The study focuses solely on maize during peak growth stages. Extending the analysis to other crops (e.g., wheat, rice) or varying growth phases would strengthen the applicability of the findings. 

   - Suggestion: A brief discussion on how the models might adapt to other crops or seasons would be beneficial. 

2. Frequency Band Restriction:

   - The experiments are limited to 433 MHz. Comparisons with LoRa’s other ISM bands (e.g., 868 MHz, 915 MHz) would highlight frequency-dependent propagation effects. 

   - Suggestion: Address this limitation in the "Discussion" section and propose future work on multi-frequency validation. 

3. Antenna Height Constraints:

   - Transmitter heights are capped at 10 meters, which may not cover all real-world scenarios (e.g., drone-mounted antennas). 

   - Suggestion: Acknowledge this constraint and suggest testing higher elevations in future studies. 

4. Model Validation:

   - While the validation in Inner Mongolia is commendable, additional datasets from other regions (e.g., tropical or humid climates) could further verify the models’ robustness. 

   - Suggestion: Mention this as a future research direction. 

5. Clarity in Figures:

   - Some figures (e.g., Figure 6a/b, 7a/b) have axis labels or legends that could be more descriptive. 

   - Suggestion: Ensure all axes are explicitly labeled (e.g., "Distance (m)" and "RSSI (dBm)"). 

Recommendation

The manuscript is ‘acceptable for publication’ pending minor revisions to address the above points. The study’s contributions to LoRa propagation modeling in agricultural settings are significant, and the methodological approach aligns with high academic standards. 

Specific Revisions Required: 

1. Expand the "Discussion" to clarify limitations (generalizability, frequency bands, antenna heights).
2. Improve figure labels for clarity.
3. Propose future work (e.g., multi-crop/multi-frequency studies, higher antenna configurations).

Additional Notes 

- The English language is generally fluent, but a final proofread for minor grammatical errors (e.g., tense consistency, article usage) is recommended. 

- The references are well-selected and up-to-date, supporting the technical background effectively. 

Overall Rating: accept with minor revisions 

Author Response

Comments 1:

Expand the "Discussion" to clarify limitations (generalizability, frequency bands, antenna heights).

Response 1:

Thank you for your suggestion. We have expanded the discussion on the page of 22

 

Comments 2:

Improve figure labels for clarity.

Response 2:

Thank you for your suggestion. We have changed the picture 11,13,21,23

Comments 3:

Propose future work (e.g., multi-crop/multi-frequency studies, higher antenna configurations).

Response 3:

Thank you for your suggestion. We have revised the last paragraph and incorporated the content you suggested.

Round 3

Reviewer 1 Report

Comments and Suggestions for Authors

The paper notably improved after its revision, and I have no further comments.