======= Review 1 ======= Relevance 4: Good match Novelty 3: Incremental Contribution 2: Minor contribution Presentation 4: Clear Recommendation 3: Possible accept Comments 1. The paper presents a variation on the SoTA. 2. The contribution is simulation based, and provides some intuitive insights but no solid treatment. The supposed log-distance propagation model is overly simplistic. 3. The paper is easy to follow. 4. Overall, the paper could be accepted if there is room for acceptance. ======= Review 2 ======= Relevance 4: Good match Novelty 2: Derivative Contribution 2: Minor contribution Presentation 4: Clear Recommendation 3: Possible accept Comments The paper investigates the affect of carrier sense in a specific wireless network simulation scenario. So the topic is a good fit. The specificity of simulations to IoT is not well described. 1. The work investigates the aspect of setting a different carrier sense threshold which is well investigated in the state of the art, see "Kim, Tae-Suk, Hyuk Lim, and Jennifer C. Hou. "Improving spatial reuse through tuning transmit power, carrier sense threshold, and data rate in multihop wireless networks." Proceedings of the 12th annual international conference on Mobile computing and networking. ACM, 2006." 2. The paper is really well written and it was definitely easy to follow. There are couple of minor typos such as "ineterest" at the last sentence of section 2. The illustration of the results could be improved the legends and the markers are too small. 3. Even though the contribution is limited, the paper is easy to read and understand. If the authors re-formulate their contributions in the way that it reflects the results they are presenting and limit the scope of novelty by extending their state of the art research. I think this paper can be accepted. The papers evaluates CCA threshold for IoT networks (a specific scenario). However, the definition of IoT networks is missing. The authors need to be more specific about how they are different compared to mobile cellular networks or indoor networks. The traffic they present is a typical periodic traffic which is frequently considered in the state of the art, thus how those this work differentiate from those works? The third contribution is vague. Please be more precise. Please re-check the state of the art for the fourth contribution. Unless there is a fundemental difference in the scenario you are considering compared to previous state of the art that analyzed CCA threshold I wouldn't call this a contribution. The last sentence of Section II mentions a traffic model, which is not explained well enough to highlight the difference with state of the art. From the next section we understand that it is periodic, I wouldn't call this a specific traffic pattern compared to state of the art. Packet success rate is not clearly defined, is it the probability that a single packet transmission is successful or a packet is not dropped after all $M$ transmissions? I am curious about why a lower threshold than -99dBm is not considered for the threshold it would be interesting to observe lower thresholds. Also the effect of interference in ISM band is neglected. I would say this is a major factor that can affect the CCA thresholding performance. ======= Review 3 ======= Relevance 5: Perfect match Novelty 3: Incremental Contribution 3: Worthwhile contribution Presentation 3: Adequate Recommendation 3: Possible accept Comments 1. Since this is a simulation only study, I would regard it essential in this era that you keep your simulator accessible on a github (or similar) repository. That is the minimum for the sake of reproducibility and convincing your readers. 2. The language is okay, by and large, apart from a few grammatically awkward phrases/clauses: e.g., "...when looking at..." (abstract); "a double interest" (you may write "twofold interest"); "...the rate of nodes in the cell..." (maybe you mean "the proportion of nodes..."). Figures 1 and 2 do not give a clear indication of the level of contention involved. Without a clear depiction of the packet generation model, merely putting in a number for the number of nodes is insufficient. Accordingly, the authors' bafflement at "an important MAC layer parameter (i.e. the maximum number of retransmissions) not having a major impact on the global network performance" is somewhat unwarranted as it relies on the assumed buffering/traffic model and persistence in contention. There should have been more causal revelations and interpretations on points like that. The quantity you define as "CCA conflict rate" is not entirely convincing in making its case; it belies its name as increasing the conflict yields higher packet success probability and lower 'On time'. ======= Review 4 ======= Relevance 4: Good match Novelty 2: Derivative Contribution 2: Minor contribution Presentation 2: Needs work Recommendation 3: Possible accept Comments In this paper authors consider CSMA as a MAC layer mechanism, instead of ALOHA. Major problem is that authors did not consider at which expense CSMA is coming. What are the energy requirements, and is it really possible to do so in IoT networks. Simulation scheme is missing, it is not clear where the results came from? I read the text, but the figure is missing. English should be deeply revised. ********************************************************************************************************************************************************************* Comments for previous version submitted at CCCN 2020 ********************************************************************************************************************************************************************* ======= Review 1 ======= *** Overall Rating: What is your overall recommendation for the paper? Accept (10-30%) (3) *** Relevance: How relevant is the topic of this paper to CCNC? Relevant (3) *** Novelty: How novel is the approach/topic presented in the paper? Minor tweak of prior schemes (1) *** Technical Strength: Is the paper technically sound and correct Technical solid (3) *** Presentation: What is the quality of presentation of the paper? The paper is overall well written. There are small flaws that are correctable. (3) *** Reviewer Confidence: How comfortable are you in the review decision? Somewhat comfortable reviewing (but not my area) (1) *** Short Summary: Please give a short summary of the paper This paper analyzes the influence of different CCA threshold on the performance of the IoT network. The result of it shows that we can get performance improvement from several nodes if using different CCA threshold in the network. *** Main Strengths (Reasons to Accept): What are the main arguments to accept the paper? 1. This paper discussed the influence of different CCA thresholds on IoT networks performance which has benefits for the implementation of CSMA on IoT networks, such as LoRa and Sigfox. 2. The article is logically clear and the language is clear. *** Main Weaknesses (Reasons to reject): What are the main arguments to reject the paper? The topic of this paper is not so much novel. *** Detailed Comments: Please input additional detailed comments below. In this paper, the author tried to figure out the impact of different CCA thresholds on IoT networks performance. And of course, it is valuable. He discussed the impact of the CCA threshold on the performance of the IoT network in several ways and introduced a new metric to assess the influence of hidden terminals. At last, with the results of several simulation experiments, the author demonstrated that the fitness between nodes can be improved if different CCA thresholds are used in the network. In summary, the structure of this paper is clear and the interpretation for some phenomenon is reasonable. However, I think it still has some problems need to be solved: 1. In section , the author said It is curious to (i.e. the maximum number of retransmissions) is not having a major impact on global network performance. However, we can see in all figures the author displayed in this paper that the change of the maximum number of retransmissions does have a significant effect on the performance of the network. 2. The legends are a bit problematic. For example, in Fig.1, the author specified in figure(a) that his experiments did not contain ACK, however, he didnt mention it in figure(b). ======= Review 2 ======= *** Overall Rating: What is your overall recommendation for the paper? Marginal (30-50%) (2) *** Relevance: How relevant is the topic of this paper to CCNC? Relevant (3) *** Novelty: How novel is the approach/topic presented in the paper? Some novel component (2) *** Technical Strength: Is the paper technically sound and correct Minor flaws but conclusions are still believable (2) *** Presentation: What is the quality of presentation of the paper? The paper is overall well written. There are small flaws that are correctable. (3) *** Reviewer Confidence: How comfortable are you in the review decision? Somewhat comfortable reviewing (but not my area) (1) *** Short Summary: Please give a short summary of the paper The authors of this paper investigated the impact of the carrier sense threshold parameter in the IoT scenarios. The simulation results show that, the communication performance of the IoT nodes is strongly correnlated with the percentage of contending nodes that they can sense. *** Main Strengths (Reasons to Accept): What are the main arguments to accept the paper? The simulations are comrephensive to identify the impact of the carrier sense parameters. The chosen simulation metrics are interesting. *** Main Weaknesses (Reasons to reject): What are the main arguments to reject the paper? The weaknesses are in two-fold. First, the scenarios seem to the same with other wireless sensor networks, which missed some salient features in the mentioned IoT scenarios, in terms of the network architecture and communication parameters. Second, there is no enough mathmatical model for the analysis, the only simulation results is not enough for a improved scheme proposal. *** Detailed Comments: Please input additional detailed comments below. ======= Review 3 ======= *** Overall Rating: What is your overall recommendation for the paper? Marginal (30-50%) (2) *** Relevance: How relevant is the topic of this paper to CCNC? Relevant (3) *** Novelty: How novel is the approach/topic presented in the paper? Some novel component (2) *** Technical Strength: Is the paper technically sound and correct Technical solid (3) *** Presentation: What is the quality of presentation of the paper? The paper is overall well written. There are small flaws that are correctable. (3) *** Reviewer Confidence: How comfortable are you in the review decision? Comfortable reviewing the paper (close to my area) (2) *** Short Summary: Please give a short summary of the paper This paper introduces the carrier sense mechanisms to the IoT and investigates the impact of the carrier sense threshold parameter in dealing with the hidden terminal problem. The simulation results demonstrate that the heterogeneous CCA Thresholds in the network can achieve an increased fairness among nodes. *** Main Strengths (Reasons to Accept): What are the main arguments to accept the paper? This paper provide a great deal of detailed simulations and experiments. *** Main Weaknesses (Reasons to reject): What are the main arguments to reject the paper? With simply simulation results provided, this paper lacks theoretical contributions and innovative insights in the algorithm. *** Detailed Comments: Please input additional detailed comments below. It seems that this should be “curves’ shapes” rather than “curves shapes” in Part A of Section IV. And it should be “two axes” instead of “two axis” in both Part A and Part B of Section V ======= Review 4 ======= *** Overall Rating: What is your overall recommendation for the paper? Reject (50-75%) (1) *** Relevance: How relevant is the topic of this paper to CCNC? Relevant (3) *** Novelty: How novel is the approach/topic presented in the paper? Minor tweak of prior schemes (1) *** Technical Strength: Is the paper technically sound and correct Technical solid (3) *** Presentation: What is the quality of presentation of the paper? The paper is overall well written. There are small flaws that are correctable. (3) *** Reviewer Confidence: How comfortable are you in the review decision? Comfortable reviewing the paper (close to my area) (2) *** Short Summary: Please give a short summary of the paper This paper studies the impact of carrier sense threshold, which is one important threshold in clear channel assessment (CCA), on the behaviour of the network both globally and locally. For this main purpose, CCA conflict rate is introduced, which shows the ratio of nodes in the cell considering a node is in conflict. However, the results show little novelty and the reason behind the findings is not investigated. *** Main Strengths (Reasons to Accept): What are the main arguments to accept the paper? The motivation for investigating the impact of the CCA threshold is good. The CCA conflict rate is a good way to show how much a node is conflicted with the other nodes, within the detection zone. *** Main Weaknesses (Reasons to reject): What are the main arguments to reject the paper? In section IV, the maximum number of retransmissions is considered as not having a major impact on the network. This conclusion only based on two values of it, 7 and 3. It would be helpful to understand the network behaviour if more results on other values are shown. Is there a certain point after which the maximum number of retransmissions will not impact the network much? The same issue also applies to the later discussion on the CCA threshold. Since the conclusion is based on only two measurements, 7 and 3, the extreme condition should be considered by providing more results on other settings. In section V part A, results show heterogeneous behaviours of different nodes. The reason for it is not discussed. What caused the different behaviours? Would that be related to topology since the deployment of nodes is mentioned at the beginning of section VI? At the beginning of section V, they mentioned in the literature the nodes have a large carrier sense range, covering all of their contenders so the CCA threshold is lowered in this paper. Lower CCA threshold means lower visibility of hidden nodes so some nodes perform badly, which did not show any novelty. Then the CCA threshold is increased for those nodes with bad performance and their local performance increased. There should be a comparison between high CCA threshold used globally and locally to see if there is a need to lower some nodes' ability to avoid collisions. For example, would there be huge amount of energy-saving? *** Detailed Comments: Please input additional detailed comments below. In the introduction, the full name of CCA is wrong. ********************************************************************************************************************************************************************* Comments for previous version submitted at PIMRC 2019 ********************************************************************************************************************************************************************* ======= PIMRC 2019 Review 1 ======= *** Relevance and Timeliness: Rate the importance and timeliness of the topic addressed in the paper within its area of research. Good. (4) *** Technical Content and Scientific Rigour: Rate the technical content of the paper (e.g.: completeness of the analysis or simulation study, thoroughness of the treatise, accuracy of the models, etc.), its soundness and scientific rigour. Solid work of notable importance. (4) *** Novelty and Originality: Rate the novelty and originality of the ideas or results presented in the paper. Significant original work and novel results. (4) *** Quality of Presentation: Rate the paper organization, the quality of text, English, and figures and the completeness and accuracy of references. Well written. (4) *** Strong Aspects: Comments to the author: What are the strong aspects of the paper? The paper studies the impact of the carrier sense threshold parameter in the context of IoT networks. The authors use NS-3 to investigate how the CCA threshold changes the carrier sense range and influences packet success probability and energy consumption. The simulation results show that the performance of nodes is strongly correlated with the percentage of contending nodes that they can sense. Strengths The study sheds light on the problem that usually is not taken into account in performance studies. It brings interesting results that should be considered when designing new access methods for IoT networks. *** Weak Aspects: Comments to the author: What are the weak aspects of the paper? The authors adopt the assumptions that not really correspond to an IoT network (CSMA/CA, 5.180 GHz)---it's not 802.11ah, nor LoRa, nor SIGFOX etc. Thus, the conclusions have limited scope. The definition of the conflict rate should be refined. I understand the objective: it should show the ratio of nodes in the cell with which the considered node is in conflict. But, the actual definition is: the mean over i of (ratio of the number of frames received by node A to the total Txi frames transmitted by node i). As I understand, nodes send packets and receive ACKs. They do not receive data packets. So, I suspect that the ratio should be: the number of detected transmissions by node A to the total Txi frames transmitted by node i, or something similar that reflects the contention with other nodes in the carrier sense area. *** Recommended Changes: Recommended changes. Please indicate any changes that should be made to the paper if accepted. Please refine the definition of the conflict rate. The paper is well written. Some remarks to improve presentation: • > change many verbs in present continuous tense into simple present tense, e.g., "Most of these technologies are using Aloha..." -> Most of these technologies use Aloha... "we see that changing the CCA threshold is not having any impact..." -> we see that changing the CCA threshold does not impact... etc. • > with a n individual performance -> just "with individual performance" • > "We believe that this second metric is a good generic proxy for the energy consumption of a node." -> We believe that this second metric represents well energy consumption of a node. • > "In this case, we see that the lowest CCA threshold value we use is giving a slightly better performance for all network densities than the other CCA threshold values, which are obtaining very similar PSPs." -> In this case, we see that the lowest CCA threshold value results in slightly better performance for all network densities than for other CCA threshold values with very similar PSPs. *** Submission Policy: Does the paper list the same author(s), title and abstract (minor wording differences in the abstract are ok) in its PDF file and EDAS registration? OK. ======= PIMRC 2019 Review 2 ======= *** Relevance and Timeliness: Rate the importance and timeliness of the topic addressed in the paper within its area of research. Acceptable. (3) *** Technical Content and Scientific Rigour: Rate the technical content of the paper (e.g.: completeness of the analysis or simulation study, thoroughness of the treatise, accuracy of the models, etc.), its soundness and scientific rigour. Valid work but limited contribution. (3) *** Novelty and Originality: Rate the novelty and originality of the ideas or results presented in the paper. Minor variations on a well investigated subject. (2) *** Quality of Presentation: Rate the paper organization, the quality of text, English, and figures and the completeness and accuracy of references. Readable, but revision is needed in some parts. (3) *** Strong Aspects: Comments to the author: What are the strong aspects of the paper? It investigated how to use Carrier sensing in IoT networks and how to select the threshold of CCA. *** Weak Aspects: Comments to the author: What are the weak aspects of the paper? All the results were based on simulation. It did not notice the hidden node phenominon and also did not show in what case the CCA threshold can not work well. Maybe thoeretical analysis may give more insights. *** Recommended Changes: Recommended changes. Please indicate any changes that should be made to the paper if accepted. All the results were based on simulation. It did not notice the hidden node phenominon and also did not show in what case the CCA threshold can not work well. Maybe thoeretical analysis may give more insights. It needs to add some theoretical analysis. *** Submission Policy: Does the paper list the same author(s), title and abstract (minor wording differences in the abstract are ok) in its PDF file and EDAS registration? yes ======= PIMRC 2019 Review 3 ======= *** Relevance and Timeliness: Rate the importance and timeliness of the topic addressed in the paper within its area of research. Good. (4) *** Technical Content and Scientific Rigour: Rate the technical content of the paper (e.g.: completeness of the analysis or simulation study, thoroughness of the treatise, accuracy of the models, etc.), its soundness and scientific rigour. Valid work but limited contribution. (3) *** Novelty and Originality: Rate the novelty and originality of the ideas or results presented in the paper. Some interesting ideas and results on a subject well investigated. (3) *** Quality of Presentation: Rate the paper organization, the quality of text, English, and figures and the completeness and accuracy of references. Well written. (4) *** Strong Aspects: Comments to the author: What are the strong aspects of the paper? The authors propose to study the impact of modifying the clear channel assignment (CCA) threshold for IoT systems. The analysis is based solely on simulations and reasonable conclusions are reached. *** Weak Aspects: Comments to the author: What are the weak aspects of the paper? The authors do not clarify how the different features of IoT traffic call for a new study on this classical aspect. No analysis is provided. *** Recommended Changes: Recommended changes. Please indicate any changes that should be made to the paper if accepted. Please address the comments above. *** Submission Policy: Does the paper list the same author(s), title and abstract (minor wording differences in the abstract are ok) in its PDF file and EDAS registration? yes ======= PIMRC 2019 Review 4 ======= *** Relevance and Timeliness: Rate the importance and timeliness of the topic addressed in the paper within its area of research. Acceptable. (3) *** Technical Content and Scientific Rigour: Rate the technical content of the paper (e.g.: completeness of the analysis or simulation study, thoroughness of the treatise, accuracy of the models, etc.), its soundness and scientific rigour. Valid work but limited contribution. (3) *** Novelty and Originality: Rate the novelty and originality of the ideas or results presented in the paper. Some interesting ideas and results on a subject well investigated. (3) *** Quality of Presentation: Rate the paper organization, the quality of text, English, and figures and the completeness and accuracy of references. Well written. (4) *** Strong Aspects: Comments to the author: What are the strong aspects of the paper? The problem studied is well explained. ns-3 based simulation results are presented for a single IoT cell with nodes transmitting on UL using CSMA/CA MAC protocol. The claim is that nodes should use different clear-channel assignment (CCA) thresholds to improve performance of all nodes. This is proven for an example network with varying load, stating that network topology, traffic characteristics and node density have a big impact on the findings. *** Weak Aspects: Comments to the author: What are the weak aspects of the paper? The new idea introduced is strange and so are the results: Nodes that would have a low packet-success probability (PSP) in a homogeneous network (all nodes using the same CCA threshold) should use a lower CCA threshold than others, thereby forming a heterogeneous nodes network. It is not said how nodes are made aware that they should deviate from the standard value of CCA threshold. *** Recommended Changes: Recommended changes. Please indicate any changes that should be made to the paper if accepted. The term "transmit opportunity" is occupied by IEEE 802.11e, as TXOP. *** Submission Policy: Does the paper list the same author(s), title and abstract (minor wording differences in the abstract are ok) in its PDF file and EDAS registration? Same authors, same abstract: Yes ======= PIMRC 2019 Review 5 ======= *** Relevance and Timeliness: Rate the importance and timeliness of the topic addressed in the paper within its area of research. Good. (4) *** Technical Content and Scientific Rigour: Rate the technical content of the paper (e.g.: completeness of the analysis or simulation study, thoroughness of the treatise, accuracy of the models, etc.), its soundness and scientific rigour. Valid work but limited contribution. (3) *** Novelty and Originality: Rate the novelty and originality of the ideas or results presented in the paper. Some interesting ideas and results on a subject well investigated. (3) *** Quality of Presentation: Rate the paper organization, the quality of text, English, and figures and the completeness and accuracy of references. Readable, but revision is needed in some parts. (3) *** Strong Aspects: Comments to the author: What are the strong aspects of the paper? Interesting paper which discusses the advantages deriving by using a possibly adaptive Carrier Sensing Mechanism in an IoT network, from the energetic and the fairness viewpoint. *** Weak Aspects: Comments to the author: What are the weak aspects of the paper? All results are obtained through simulation, and this limits significantly the scientific contribution of the paper. Furthermore, some results seem preliminary (for example, the comparison with Aloha, and the threshold adaptation algorithm), requiring further investigations. *** Recommended Changes: Recommended changes. Please indicate any changes that should be made to the paper if accepted. The presentation is acceptable. However, the figures and the labels are difficult to read (average values should be put better into evidence). The text is a bit colloquial. *** Submission Policy: Does the paper list the same author(s), title and abstract (minor wording differences in the abstract are ok) in its PDF file and EDAS registration? Yes