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Kumar Jha, Rakesh, und Pooja Kharga. „A Comparative Performance Analysis of Routing Protocols in MANET using NS3 Simulator“. International Journal of Computer Network and Information Security 7, Nr. 4 (08.03.2015): 62–68. http://dx.doi.org/10.5815/ijcnis.2015.04.08.
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Naik, Lakshman, R. U. und R. B. „Analysis of Node Velocity Effects in MANET Routing Protocols using Network Simulator (NS3)“. International Journal of Computer Applications 144, Nr. 4 (17.06.2016): 1–5. http://dx.doi.org/10.5120/ijca2016910225.
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Luo, Chaohui, Biyun Ma, Fangjiong Chen, Quansheng Guan, Hua Yu und Fei Ji. „Multicore-Processor Based Software-Defined Communication/Network Platform for Underwater Internet of Things“. Sensors 19, Nr. 23 (26.11.2019): 5168. http://dx.doi.org/10.3390/s19235168.
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Software-defined acoustic modems (SDAMs) for underwater communication and networking have been an important research topic due to their flexibility and programmability. In this paper, we propose a reconfigurable platform for SDAMs based on the TI AM5728 processor, which integrates dual-core ARM Cortex-A15 CPUs and two TI C66x DSP cores. The signal processing and A/D, D/A for physical-layer communication are implemented in the DSP cores. The networking protocols and the application programs are implemented in the ARM cores. The proposed platform has the following characteristics: (1) Due to the high-performance dual-ARM cores, the whole NS3 network simulator can be run in the ARM cores. Network protocols developed in a software simulation platform (e.g., NS3 platform) can be seamlessly migrated to a hardware platform without modification. (2) A new physical-layer module associated with real acoustic channel is developed, such that a data packet generated from the application layer will be transmitted through a real acoustic channel. The results of networking experiments with five nodes are presented to demonstrate the effectiveness of the proposed platform.
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Khalil, N., und A. Najid. „Performance analysis of 802.11ac with frame aggregation using NS3“. International Journal of Electrical and Computer Engineering (IJECE) 10, Nr. 5 (01.10.2020): 5368. http://dx.doi.org/10.11591/ijece.v10i5.pp5368-5376.
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802.11ac is an interesting standard of IEEE bringing multiple advantages than its predecessor 802.11n. 802.11ac is faster and more scalable version of 802.11n offering the capabilities of wireless Gigabit Ethernet. 802.11ac will enable access points (AP) to support more STAs with a better experience for clients and more channel bonding increasing from a maximum of 40 MHz with 802.11n up to 80 or 160 MHz with 802.11ac standard. In this paper, we analyze and evaluate the 802.11ac performance using NS3 simulator (v3.26) relying on several features like channel bonding, modulation and coding schemes, guard interval and frame aggregation. Then, we present the effect of the variation of distance between STAs and AP on the network performance in term of throughput. Finally, we capture the most relevant simulations outcomes and we indicate some research challenges for the future work.
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Lavacca, Francesco G., Pierpaolo Salvo, Ludovico Ferranti, Andrea Speranza und Luca Costantini. „Performance Evaluation of 5G Access Technologies and SDN Transport Network on an NS3 Simulator“. Computers 9, Nr. 2 (27.05.2020): 43. http://dx.doi.org/10.3390/computers9020043.
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In this article, we deal with the enhanced Mobile Broadband (eMBB) service class, defined within the new 5G communication paradigm, to evaluate the impact of the transition from 4G to 5G access technology on the Radio Access Network and on the Transport Network. Simulation results are obtained with ns3 and performance analyses are focused on 6 GHz radio scenarios for the Radio Access Network, where an Non-Standalone 5G configuration has been assumed, and on SDN-based scenarios for the Transport Network. Inspired by the 5G Transformer model, we describe and simulate each single element of the three main functional plains of the proposed architecture to aim a preliminary evaluation of the end-to-end system performances.
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Zagrouba, Rachid, und Amine Kardi. „Comparative Study of Energy Efficient Routing Techniques in Wireless Sensor Networks“. Information 12, Nr. 1 (18.01.2021): 42. http://dx.doi.org/10.3390/info12010042.
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This paper surveys the energy-efficient routing protocols in wireless sensor networks (WSNs). It provides a classification and comparison following a new proposed taxonomy distinguishing nine categories of protocols, namely: Latency-aware and energy-efficient routing, next-hop selection, network architecture, initiator of communication, network topology, protocol operation, delivery mode, path establishment and application type. We analyze each class, discuss its representative routing protocols (mechanisms, advantages, disadvantages…) and compare them based on different parameters under the appropriate class. Simulation results of LEACH, Mod-LEACH, iLEACH, E-DEEC, multichain-PEGASIS and M-GEAR protocols, conducted under the NS3 simulator, show that the routing task must be based on various intelligent techniques to enhance the network lifespan and guarantee better coverage of the sensing area.
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Wu, Xu. „Context-Aware Cloud Service Selection Model for Mobile Cloud Computing Environments“. Wireless Communications and Mobile Computing 2018 (2018): 1–14. http://dx.doi.org/10.1155/2018/3105278.
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Mobile cloud computing (MCC) has attracted extensive attention in recent years. With the prevalence of MCC, how to select trustworthy and high quality mobile cloud services becomes one of the most urgent problems. Therefore, this paper focuses on the trustworthy service selection and recommendation in mobile cloud computing environments. We propose a novel service selection and recommendation model (SSRM), where user similarity is calculated based on user context information and interest. In addition, the relational degree among services is calculated based on PropFlow algorithm and we utilize it to improve the accuracy of ranking results. SSRM supports a personalized and trusted selection of cloud services through taking into account mobile user’s trust expectation. Simulation experiments are conducted on ns3 simulator to study the prediction performance of SSRM compared with other two traditional approaches. The experimental results show the effectiveness of SSRM.
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Aldalbahi, Adel, Michael Rahaim, Abdallah Khreishah, Moussa Ayyash und Thomas D. C. Little. „Visible Light Communication Module: An Open Source Extension to the ns3 Network Simulator With Real System Validation“. IEEE Access 5 (2017): 22144–58. http://dx.doi.org/10.1109/access.2017.2759779.
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Sahnoun, Abdelkabir, Ahmed Habbani und Jamal El Abbadi. „An Energy-Efficient Proactive Routing Scheme for MANET: Game Theoretical Approach of Forwarding with Selfish Nodes“. International Journal of Electronics and Telecommunications 63, Nr. 4 (27.11.2017): 399–404. http://dx.doi.org/10.1515/eletel-2017-0055.
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Abstract In Mobile Ad-hoc Networks, nodes exchange packets with each other using intermediate nodes as relays. Since nodes in MANETs are battery powered, energy conservation is a crucial issue. Accepting relay all request may not be in the best interest of a node. But if many nodes prefer not to consume energy in relaying packets on behalf of others, the overall performance of routing in network will be influenced. In this paper we address the energy-efficient routing problem in MANETs with selfish nodes. We modeled this problem as a game-theoretic constraint optimization; we defined the utility of each node as a weighted difference between a performance metric and some transmission costs. A motivate mechanism is proposed in order to induce nodes to forwarding cooperation. Each node independently implements the optimal equilibrium strategy under the given constraints. Simulation results by NS3 simulator show that our proposed approach can improve system performance in network lifetime and packet delivery ratio.
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Agamy, Adel, und Ahmed M. Mohamed. „Influence of various application types on the performance of LTE mobile networks“. International Journal of Electrical and Computer Engineering (IJECE) 10, Nr. 5 (01.10.2020): 5420. http://dx.doi.org/10.11591/ijece.v10i5.pp5420-5429.
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Modern mobile internet networks are becoming heavier and denser. Also it is not regularly planned, and becoming more heterogeneous. The explosive growth in the usage of smartphones poses numerous challenges for LTE cellular networks design and implementation. The performance of LTE networks with bursty and self-similar traffic has become a major challenge. Accurate modeling of the data generated by each connected wireless device is important for properly investigating the performance of LTE networks. This paper presents a mathematical model for LTE networks using queuing theory considering the influence of various application types. Using sporadic source traffic feeding to the queue of the evolved node B and with the exponential service time assumption, we construct a queuing model to estimate the performance of LTE networks. We use the performance model presented in this paper to study the influence of various application categories on the performance of LTE cellular networks. Also we validate our model with simulation using NS3 simulator with different scenarios.
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Centelles, Diego, Antonio Soriano-Asensi, José Vicente Martí, Raúl Marín und Pedro J. Sanz. „Underwater Wireless Communications for Cooperative Robotics with UWSim-NET“. Applied Sciences 9, Nr. 17 (28.08.2019): 3526. http://dx.doi.org/10.3390/app9173526.
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The increasing number of autonomous underwater vehicles (AUVs) cooperating in underwater operations has motivated the use of wireless communications. Their modeling can minimize the impact of their limited performance in real-time robotic interventions. However, robotic frameworks hardly ever consider the communications, and network simulators are not suitable for HIL experiments. In this work, the UWSim-NET is presented, an open source tool to simulate the impact of communications in underwater robotics. It gathers the benefits of NS3 in modeling communication networks with those of the underwater robot simulator (UWSim) and the robot operating system (ROS) in modeling robotic systems. This article also shows the results of three experiments that demonstrate the capabilities of UWSim-NET in modeling radio frequency (RF) and acoustic links in underwater scenarios. It also permits evaluating several MAC protocols such as additive links online Hawaii area (ALOHA), slotted floor acquisition multiple access (S-FAMA) and user defined protocols. A third experiment demonstrated the excellent capabilities of UWSim-NET in conducting hardware in the loop (HIL) experiments.
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Pasha, Muhammad Adeel, Jahangir Hassan Khan und Shahid Masud. „I-LEACH: energy-efficient routing protocol for monitoring of irrigation canals“. SIMULATION 91, Nr. 8 (August 2015): 750–64. http://dx.doi.org/10.1177/0037549715602957.
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Irrigation canals and their tributaries, originating from the run of a river, span a considerable geographical area that is typically of the order of 100 km2. Efficient deployment of wireless sensor networks (WSNs) to monitor and control the flow of scarce water resources is a challenging task, mainly because the WSN motes are designed to consume very low power and communicate over very short distances. This paper investigates the use of different WSN protocols to monitor water usage over irrigation networks in the province of Punjab, Pakistan. This irrigation network is considered to be among the biggest in the world with over 58,000 canal outlets. The paper proposes a new energy-efficient routing protocol that improves the network lifespan as well as the packet error rates resulting in a more dependable distributed WSN. The protocol was simulated along with other state-of-the-art protocols in random as well as linear topologies with simulation variables such as the number of nodes, coverage area and base station position varied in each case. The results also show that the node die-out pattern in our protocol is uniformly spread throughout the network as compared with other existing protocols resulting in increased robustness. The NS3 network simulator was used to simulate the geographically distributed WSN with different protocols and system parameters.
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Wang, Hui, Junyong Tang und Bo Hong. „Research of Wireless Congestion Control Algorithm Based on EKF“. Symmetry 12, Nr. 4 (17.04.2020): 646. http://dx.doi.org/10.3390/sym12040646.
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The random variation of bandwidth in wireless networks causes some significant challenges to the congestion control protocols based on bandwidth estimation. In this paper, a wireless congestion control scheme based on extended Kalman filtering and bandwidth (CSEKB) is proposed. The CSEKB can effectively perceive the bandwidth oscillation of wireless networks and distinguish the type of packet loss by establishing a noise perception factor. According to the congestion factor, the congestion control parameters are adjusted to correspondingly improve the performance of the wireless network. Moreover, the variation trend of the size of the congestion window presents a law of similar normal distribution curve, which has a certain degree of local symmetry. The CSEKB was implemented in Network simulator 3 (NS3) and compared with TCP Westwood (TCPW), CUBIC, and extended Kalman filtering-based bandwidth estimation (EBE). Through extensive simulation studies, the proposed CSEKB demonstrated the significant performance in wireless networks. First, the CSEKB can achieve congestion control based on the accurate prediction of available bandwidth, and improve average throughput and link utilization. In addition, the CSEKB has good fairness and friendliness compared with several other well-known congestion control methods.
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Santoso, Iman Hedi, Kalamullah Ramli und Suryadi M.T. „TLS-VaD: A New Tool for Developing Centralized Link-Scheduling Algorithms on the IEEE802.15.4e TSCH Network“. Electronics 8, Nr. 12 (17.12.2019): 1555. http://dx.doi.org/10.3390/electronics8121555.
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A simulator plays an important role in network protocol research, as it enables researchers to develop protocols more flexibly. Many simulators have been developed to support research in this field, including NS-2, NS-3, OPNET, OMNeT, and Cooja. Although, as a research support tools, NS3 and Cooja have already been equipped with an Internet of things (IoT) module, their support for research on IoT centralized scheduling is still limited. Therefore, this study is aimed to develop a tool for IoT centralized scheduling research, where the IoT technology is based on the IEEE802.15.4e time synchronized channel hopping (TSCH) standard. The tool is called the TSCH Link-Scheduling visualization and data processing (TLS-VaD). The results of validity tests show that TLS-VaD works well; therefore, this tool can be used in the performance measurement of centralized scheduling algorithms on TSCH networks. As an example of the application, this research used TLS-VaD to test the performance of three scheduling algorithms: Iman Ramli Bursty Transmission Scheduling Algorithm (IRByTSA), first top scheduling algorithm (FTSA), and first leaf scheduling algorithm (FLSA). The test results using TLS-VaD shows that IRByTSA had better performance compared to FLSA and FTSA, because it saved more power and was able to generate scheduling decisions relatively quickly.
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Trew, Alex. „Endogenous Infrastructure Development and Spatial Takeoff in the First Industrial Revolution“. American Economic Journal: Macroeconomics 12, Nr. 2 (01.04.2020): 44–93. http://dx.doi.org/10.1257/mac.20160162.
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This paper develops a model in which the evolution of the transport sector occurs alongside the growth in trade and output of agricultural and manufacturing firms. Simulation output captures aspects of the historical record of England and Wales over 1710–1881. A number of counterfactuals demonstrate the role that the timing and spatial distribution of infrastructure development play in determining the timing of takeoff. There can be a role for policy in accelerating takeoff through improving infrastructure, but the spatial distribution of that improvement matters. (JEL H54, N53, N63, N73, N93, R12, R42)
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Yu, Sang il, und Chang Yun Park. „A Responsible Airtime Approach for True Time-Based Fairness in Multi-Rate WiFi Networks“. Sensors 18, Nr. 11 (28.10.2018): 3658. http://dx.doi.org/10.3390/s18113658.
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Airtime fairness, or time-based fairness, has been well recognized as a method to solve WiFi performance anomalies and provide a balance between fairness and spectrum efficiency in multi-rate wireless networks. However, the definition of airtime is vague and simplistic. In this paper, it is demonstrated that current airtime fair scheduling results in unfairness in reality because overheads are neglected or unfairly counted. We introduce a notion of responsible airtime, which covers not only the data transmission time, but also all overheads, even a TCP ACK segment in TCP traffic. An approach based on responsible airtime can provide true time-based fairness, but responsible airtime is too complicated to directly handle. A practical method is thus introduced for evaluating responsible airtime fairness indirectly via throughput measurement. The key element, throughput fair share, of a node, is based on the baseline property in time-based fairness. For each node, an achieving ratio of actual throughput to the throughput fair share is determined, and a new fairness index considering deficiency as well as equity is applied. To validate the feasibility of responsible airtime fairness, we have developed a simple responsible airtime fair scheduler in access points for download traffic. Extensive simulation experiments are conducted in various network and traffic environments using the ns3 simulator. The results show that true time-based fairness is achievable in practice.
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Haseeb, Khalid, Ahmad Almogren, Ikram Ud Din, Naveed Islam und Ayman Altameem. „SASC: Secure and Authentication-Based Sensor Cloud Architecture for Intelligent Internet of Things“. Sensors 20, Nr. 9 (27.04.2020): 2468. http://dx.doi.org/10.3390/s20092468.
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Nowadays, the integration of Wireless Sensor Networks (WSN) and the Internet of Things (IoT) provides a great concern for the research community for enabling advanced services. An IoT network may comprise a large number of heterogeneous smart devices for gathering and forwarding huge data. Such diverse networks raise several research questions, such as processing, storage, and management of massive data. Furthermore, IoT devices have restricted constraints and expose to a variety of malicious network attacks. This paper presents a Secure Sensor Cloud Architecture (SASC) for IoT applications to improve network scalability with efficient data processing and security. The proposed architecture comprises two main phases. Firstly, network nodes are grouped using unsupervised machine learning and exploit weighted-based centroid vectors for the development of intelligent systems. Secondly, the proposed architecture makes the use of sensor-cloud infrastructure for boundless storage and consistent service delivery. Furthermore, the sensor-cloud infrastructure is protected against malicious nodes by using a mathematically unbreakable one-time pad (OTP) encryption scheme to provide data security. To evaluate the performance of the proposed architecture, different simulation experiments are conducted using Network Simulator (NS3). It has been observed through experimental results that the proposed architecture outperforms other state-of-the-art approaches in terms of network lifetime, packet drop ratio, energy consumption, and transmission overhead.
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Viana, Joseanne, Francisco Cercas, Américo Correia, Rui Dinis und Pedro Sebastião. „MIMO Relaying UAVs Operating in Public Safety Scenarios“. Drones 5, Nr. 2 (26.04.2021): 32. http://dx.doi.org/10.3390/drones5020032.
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Methods to implement communication in natural and humanmade disasters have been widely discussed in the scientific community. Scientists believe that unmanned aerial vehicles (UAVs) relays will play a critical role in 5G public safety communications (PSC) due to their technical superiority. They have several significant advantages: a high degree of mobility, flexibility, exceptional line of sight, and real-time adaptative planning. For instance, cell edge coverage could be extended using relay UAVs. This paper summarizes the sidelink evolution in the 3GPP standardization associated with the usage of the device to device (D2D) techniques that use long term evolution (LTE) communication systems, potential extensions for 5G, and a study on the impact of circular mobility on relay UAVs using the software network simulator 3 (NS3). In this simulation, the transmitted packet percentage was evaluated where the speed of the UAV for users was changed. This paper also examines the multi-input multi-output (MIMO) communication applied to drones and proposes a new trajectory to assist users experiencing unfortunate circumstances. The overall communication is highly dependent on the drone speed and the use of MIMO and suitable antennas may influence overall transmission between users and the UAVs relay. When the UAVs relaying speed was configured at 108 km/h the total transmission rate was reduced to 55% in the group with 6 users allocated to each drone.
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Pan, Wansu, Haibo Tan, Xiru Li und Xiaofeng Li. „Improved RTT Fairness of BBR Congestion Control Algorithm Based on Adaptive Congestion Window“. Electronics 10, Nr. 5 (06.03.2021): 615. http://dx.doi.org/10.3390/electronics10050615.
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To alleviate the lower performance of Transmission Control Protocol (TCP) congestion control over complex network, especially the high latency and packet loss scenario, Google proposed the Bottleneck Bandwidth and Round-trip propagation time (BBR) congestion control algorithm. In contrast with other TCP congestion control algorithms, BBR adjusted transfer data by maximizing delivery rate and minimizing delay. However, some evaluation experiments have shown that the persistent queues formation and retransmissions in the bottleneck can lead to serious fairness issues between BBR flows with different round-trip times (RTTs). They pointed out that small RTT differences cause unfairness in the throughput of BBR flows and flows with longer RTT can obtain higher bandwidth when competing with the shorter RTT flows. In order to solve this fairness problem, an adaptive congestion window of BBR is proposed, which adjusts the congestion window gain of each BBR flow in network load. The proposed algorithms alleviate the RTT fairness issue by controlling the upper limit of congestion window according to the delivery rate and queue status. In the Network Simulator 3 (NS3) simulation experiment, it shows that the adaptive congestion window of BBR (BBR-ACW) congestion control algorithm improves the fairness by more than 50% and reduces the queuing delay by 54%, compared with that of the original BBR in different buffer sizes.
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Pan, Wansu, Xiaofeng Li, Haibo Tan, Jinlin Xu und Xiru Li. „Improvement of RTT Fairness Problem in BBR Congestion Control Algorithm by Gamma Correction“. Sensors 21, Nr. 12 (16.06.2021): 4128. http://dx.doi.org/10.3390/s21124128.
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Google proposed the bottleneck bandwidth and round-trip propagation time (BBR), which is a new congestion control algorithm. BBR creates a network path model by measuring the available bottleneck bandwidth and the minimum round-trip time (RTT) to maximize delivery rate and minimize latency. However, some studies have shown that there are serious RTT fairness problems in the BBR algorithm. The flow with longer RTT will consume more bandwidth and the flows with shorter RTT will be severely squeezed or even starved to death. Moreover, these studies pointed out that even small RTT differences will lead to the throughput of BBR flows being unfair. In order to solve the problem of RTT fairness, an improved algorithm BBR-gamma correction (BBR-GC) is proposed. BBR-GC algorithm takes RTT as feedback information, and then uses the gamma correction function to fit the adaptive pacing gain. This approach can make different RTT flows compete for bandwidth more fairly, thus alleviating the RTT fairness issue. The simulation results of Network Simulator 3 (NS3) show that that BBR-GC algorithm cannot only ensure the channel utilization, but also alleviate the RTT fairness problem of BBR flow in different periods. Through the BBR-GC algorithm, RTT fairness is improved by 50% and the retransmission rate is reduced by more than 26%, compared with that of the original BBR in different buffer sizes.
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Prakash, S. P. Shiva, T. N. Nagabhushan und Kirill Krinkin. „Congestion Avoidance and Delay Minimization in Energy Aware Routing of Dynamic ieee 802.11s WMN“. International Journal of Embedded and Real-Time Communication Systems 7, Nr. 1 (Januar 2016): 85–112. http://dx.doi.org/10.4018/ijertcs.2016010105.
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Minimization of delay in collecting the data at any base stations is one of the major concerns in cluster based Wireless Mesh Networks. several researches have proposed algorithms to control congestion considering static nature of a node. Mobility of a node results in high congestion due to frequent link breakages and high energy consumption due to re-establishment of route during routing process. Hence, the authors consider dynamic nodes with single hop inside the static cluster. The proposed model includes four modules namely, Cluster head selection, slot allocation, slot scheduling and data collection process. the cluster head selection is based on the maximum energy, number of links and link duration. Slot allocation is based on the available energy () and the required energy (). Slot scheduling is carried out based on the link duration. Data at the base station will be collected as they are scheduled. Model is tested using Network Simulator-3 (NS3) and results indicate that the proposed model achieves least delay besides reducing the congestion compared to the existing methods.
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Rahman, Shaikh Mohammad Ehsanur, Farhat Anwar und Aisha Hassan Abdalla Hashim. „Performance Enhancement of NEMO based VANET using Localization Router (LR) to reduce Handoff delays“. Indonesian Journal of Electrical Engineering and Computer Science 8, Nr. 2 (01.11.2017): 511. http://dx.doi.org/10.11591/ijeecs.v8.i2.pp511-521.
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<p>Vehicular Ad hoc networks (VANETs) combined with vehicle-to-vehicle and vehicle-to-infrastructure communications can be considered as the most suitable technology to enable ITS (Intelligent Transport System) application bestowed upon travellers with mobility, safety and productivity with human comfort. As a delay sensitive ITS application, handoff delays and packet losses are critical parameters for maintaining seamless connectivity in VANET solution. During handoff, when mobile node (vehicle) is acquiring new CoA (care of address), packets directed towards that node are lost; because it’s old identity is no more valid. So in high speed dynamic vehicular environment the number of frequent handoffs would produce delay beyond the normal limit. Therefore, it is very important to resolve the issues of handoff delay and packet losses in VANET environment. As a solution, a domain based RHD-NV (Reducing Handoff Delay in NEMO based VANET) scheme is proposed in this paper. Number of vehicles moving towards the road constructs a domain where network mobility NEMO-BS protocol is applied. A vehicle is selected as MR (master router) and connected to the RSU (road side unit) to the internet and other vehicles in the domain work as LRs (localization router) and communicate through MR. Simulation tests performed in NS3 (network simulator) and MATLAB SIMULINK demonstrate that using LRs (localization router) in the domain, the number of handoffs and handoff delay are significantly reduced.</p>
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Wang, Cheng, Huiwen Wang und Weidong Wang. „A Two-Hops State-Aware Routing Strategy Based on Deep Reinforcement Learning for LEO Satellite Networks“. Electronics 8, Nr. 9 (22.08.2019): 920. http://dx.doi.org/10.3390/electronics8090920.
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Low Earth Orbit (LEO) satellite networks can provide complete connectivity and worldwide data transmission capability for the internet of things. However, arbitrary flow arrival and uneven traffic load among areas bring about unbalanced traffic distribution over the LEO constellation. Therefore, the routing strategy in LEO networks should have the ability to adjust routing paths based on changes in network status adaptively. In this paper, we propose a Two-Hops State-Aware Routing Strategy Based on Deep Reinforcement Learning (DRL-THSA) for LEO satellite networks. In this strategy, each node only needs to obtain the link state within the range of two-hop neighbors, and the optimal next-hop node can be output. The link state is divided into three levels, and the traffic forwarding strategy for each level is proposed, which allows DRL-THSA to cope with link outage or congestion. The Double-Deep Q Network (DDQN) is proposed in DRL-THSA to figure out the optional next hop by inputting the two-hops link states. The DDQN is analyzed from three aspects: model setting, training process and running process. The effectiveness of DRL-THSA, in terms of end-to-end delay, throughput, and packet drop rate, is verified via a set of simulations using the Network Simulator 3 (NS3).
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Chaaf, Amir, Mohammed Saleh Ali Muthanna, Ammar Muthanna, Soha Alhelaly, Ibrahim A. Elgendy, Abdullah M. Iliyasu und Ahmed A. Abd El-Latif. „Energy-Efficient Relay-Based Void Hole Prevention and Repair in Clustered Multi-AUV Underwater Wireless Sensor Network“. Security and Communication Networks 2021 (30.06.2021): 1–20. http://dx.doi.org/10.1155/2021/9969605.
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Underwater wireless sensor networks (UWSNs) enable various oceanic applications which require effective packet transmission. In this case, sparse node distribution, imbalance in terms of overall energy consumption between the different sensor nodes, dynamic network topology, and inappropriate selection of relay nodes cause void holes. Addressing this problem, we present a relay-based void hole prevention and repair (ReVOHPR) protocol by multiple autonomous underwater vehicles (AUVs) for UWSN. ReVOHPR is a global solution that implements different phases of operations that act mutually in order to efficiently reduce and identify void holes and trap relay nodes to avoid it. ReVOHPR adopts the following operations as ocean depth (levels)-based equal cluster formation, dynamic sleep scheduling, virtual graph-based routing, and relay-assisted void hole repair. For energy-efficient cluster forming, entropy-based eligibility ranking (E2R) is presented, which elects stable cluster heads (CHs). Then, dynamic sleep scheduling is implemented by the dynamic kernel Kalman filter (DK2F) algorithm in which sleep and active modes are based on the node’s current status. Intercluster routing is performed by maximum matching nodes that are selected by dual criteria, and also the data are transmitted to AUV. Finally, void holes are detected and repaired by the bicriteria mayfly optimization (BiCMO) algorithm. The BiCMO focuses on reducing the number of holes and data packet loss and maximizes the quality of service (QoS) and energy efficiency of the network. This protocol is timely dealing with node failures in packet transmission via multihop routing. Simulation is implemented by the NS3 (AquaSim module) simulator that evaluates the performance in the network according to the following metrics: average energy consumption, delay, packet delivery rate, and throughput. The simulation results of the proposed REVOHPR protocol comparing to the previous protocols allowed to conclude that the REVOHPR has considerable advantages. Due to the development of a new protocol with a set of phases for data transmission, energy consumption minimization, and void hole avoidance and mitigation in UWSN, the number of active nodes rate increases with the improvement in overall QoS.
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Sinde, Ramadhani, Feroza Begum, Karoli Njau und Shubi Kaijage. „Refining Network Lifetime of Wireless Sensor Network Using Energy-Efficient Clustering and DRL-Based Sleep Scheduling“. Sensors 20, Nr. 5 (10.03.2020): 1540. http://dx.doi.org/10.3390/s20051540.
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Over the recent era, Wireless Sensor Network (WSN) has attracted much attention among industrialists and researchers owing to its contribution to numerous applications including military, environmental monitoring and so on. However, reducing the network delay and improving the network lifetime are always big issues in the domain of WSN. To resolve these downsides, we propose an Energy-Efficient Scheduling using the Deep Reinforcement Learning (DRL) (E2S-DRL) algorithm in WSN. E2S-DRL contributes three phases to prolong network lifetime and to reduce network delay that is: the clustering phase, duty-cycling phase and routing phase. E2S-DRL starts with the clustering phase where we reduce the energy consumption incurred during data aggregation. It is achieved through the Zone-based Clustering (ZbC) scheme. In the ZbC scheme, hybrid Particle Swarm Optimization (PSO) and Affinity Propagation (AP) algorithms are utilized. Duty cycling is adopted in the second phase by executing the DRL algorithm, from which, E2S-DRL reduces the energy consumption of individual sensor nodes effectually. The transmission delay is mitigated in the third (routing) phase using Ant Colony Optimization (ACO) and the Firefly Algorithm (FFA). Our work is modeled in Network Simulator 3.26 (NS3). The results are valuable in provisions of upcoming metrics including network lifetime, energy consumption, throughput and delay. From this evaluation, it is proved that our E2S-DRL reduces energy consumption, reduces delays by up to 40% and enhances throughput and network lifetime up to 35% compared to the existing cTDMA, DRA, LDC and iABC methods.
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de Sena, Rodrigo Antunes, Ivan Napoleão Bastos und Gustavo Mendes Platt. „Theoretical and Experimental Aspects of the Corrosivity of Simulated Soil Solutions“. ISRN Chemical Engineering 2012 (10.12.2012): 1–6. http://dx.doi.org/10.5402/2012/103715.
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Corrosion of buried steel pipe is a permanent engineering problem and, albeit the counter measures against degradation, when the corrosion process takes place, the damage has costly impact. In order to study the corrosion behavior of pipelines, it is possible to use actual soil extracts or simulated soil solutions. The extract is much related to specific sites and consequently too strict to permit a general understanding. The simulated soil presents, as advantage, its inorganic characteristic and easy preparation. In this paper, we present some theoretical results concerning the chemical equilibria of NS1, NS2, NS3, and NS4 simulated soil solutions. Besides, we have studied the effect of the above four media in corrosion behavior and polarization curves were performed for an API 5L X65 steel. The theoretical findings show that each ionic concentration varies for a 6–12 pH range. The experimental data suggested that the corrosion currents decrease as high is the pH and increase as high is the chloride content. Notwithstanding these facts, for multielectrolyte solutions, a simple correlation with a given ion is not straightforward but the complementary approaches used here give useful insights.
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V Raj, Shruthi, und Hemanth S R. „Simulation of ACO Technique Using NS2 Simulator“. International Journal of Engineering Trends and Technology 23, Nr. 8 (25.05.2015): 403–6. http://dx.doi.org/10.14445/22315381/ijett-v23p277.
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Hu, Xiao, Yong Xiang Zhang, Yi Fan Wang und Shuo Jia Peng. „Simulation and Optimization of Compound A2/O Treatment Process Based on Model ASM3“. Advanced Materials Research 726-731 (August 2013): 2389–93. http://dx.doi.org/10.4028/www.scientific.net/amr.726-731.2389.
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Introduction is given to the content of activated sludge model No.3 (ASM3). The simulation program which based on the integration of ASM3 and Anaerobic Digestion Model was used to simulate A2/O with AquaMats Process. The predicted results of effluent COD, NH3-N and NO3-N accorded with the actuality. The removal efficiency of TP was quite low when sludge return rate was 100%. Based on this condition, the improved scheme which adjusts sludge reflux ratio to 60% was put forward and simulated. Process was optimized depending on the simulation results and the removal efficiencies of COD, NH3-N and TP reached to 83.1%, 98.75 and 24.01%. It is verified that ASM3 can be used as the platform of activated sludge process design.
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Wijekoon, Janaka, Erwin Harahap und Hiroaki Nishi. „Service-oriented Router Simulation Module Implementation in NS2 Simulator“. Procedia Computer Science 19 (2013): 478–85. http://dx.doi.org/10.1016/j.procs.2013.06.064.
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Nemade, Chetana Hemant. „Execution Evaluation of AODV Protocol Using NS2 Simulator for Emergency Automobile“. Revista Gestão Inovação e Tecnologias 11, Nr. 4 (10.07.2021): 1792–801. http://dx.doi.org/10.47059/revistageintec.v11i4.2237.
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Jin, Yun Xiao, und Jun Yao. „Biological Nutrient Removal from Simulated Domestic Wastewater in Sequencing Batch Biofilm Reactor“. Advanced Materials Research 518-523 (Mai 2012): 2406–9. http://dx.doi.org/10.4028/www.scientific.net/amr.518-523.2406.
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A lab-scale sequencing batch biofilm reactor (SBBR) was developed to treat domestic wastewater. After one year’s operation, the results were obtained as follows: when the reaction carried out in 3 h, COD removal efficiency approached or reached the maximal value, up to 90%. The nitrification process of NH3-N needed 4 h, and NH3-N removal efficiency reached the maximal value. Moreover, according to the variation of TN , NO3--N and NO2--N concentration in the nitrification and denitrification process, when NH3-N degraded to zero or the minimal value, just two cycles ending, it means that the SBBR system completed the nitrification and denitrification process.
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Wu, Chang Hang, und Wei Jun Zhang. „Evaluation of Sequencing Batch Biofilm Reactor for Biological Nutrient Removal from Simulated Domestic Wastewater“. Applied Mechanics and Materials 209-211 (Oktober 2012): 2049–52. http://dx.doi.org/10.4028/www.scientific.net/amm.209-211.2049.
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A lab-scale sequencing batch biofilm reactor (SBBR) was developed to treat domestic wastewater. After one year’s operation, the results were obtained as follows: when the reaction carried out in 3 h, COD removal efficiency approached or reached the maximal value, up to 90%. The nitrification process of NH3-N needed 4 h, and NH3-N removal efficiency reached the maximal value. Moreover, according to the variation of TN , NO3--N and NO2--N concentration in the nitrification and denitrification process, when NH3-N degraded to zero or the minimal value, just two cycles ending, it means that the SBBR system completed the nitrification and denitrification process.
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Aldeen Khairi, Teaba Wala, Azhar F. Al-zubidi und Ehsan Qahtan Ahmed. „Modified Multipath Routing Protocol Applied On Ns3 Dcell Network Simulation System“. International Journal of Interactive Mobile Technologies (iJIM) 15, Nr. 10 (25.05.2021): 208. http://dx.doi.org/10.3991/ijim.v15i10.22703.
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<p class="0abstract"><strong>—</strong>In the communication networks, guidance has become an important factor, with a significant impact on network performance, where the network orientation area has been and continues to be an ongoing development, intensive research for many years aimed at optimizing the network. This paper performs three modifications for a multipath routing protocol to solve the problem of routing in a DCell network simulation and apply online solutions on the network, the goal is to improve the transition efficiency of data. The modifications used to avoid data transmission failures which are delay problem<strong>, </strong>link failure problem, and power off (rack problem). The implementation of multipath routing protocol on the DCell network in actual simulation using the NS-3 program, which represents the rule that the DCell network was built and simulated. Finally, the modifications succeeded and return good results decreasing the delay time and solving the data transaction problems.</p>
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Zhao, Yu, Mengchen Yuan, Xin Huang, Feng Chen und Jie Zhang. „Quantification and evaluation of atmospheric ammonia emissions with different methods: a case study for the Yangtze River Delta region, China“. Atmospheric Chemistry and Physics 20, Nr. 7 (09.04.2020): 4275–94. http://dx.doi.org/10.5194/acp-20-4275-2020.
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Abstract. To explore the effects of data and method on emission estimation, two inventories of NH3 emissions of the Yangtze River Delta (YRD) region in eastern China were developed for 2014 based on constant emission factors (E1) and those characterizing agricultural processes (E2). The latter derived the monthly emission factors and activity data integrating the local information of soil, meteorology, and agricultural processes. The total emissions were calculated to be 1765 and 1067 Gg with E1 and E2, respectively, and clear differences existed in seasonal and spatial distributions. Elevated emissions were found in March and September in E2, attributed largely to the increased top dressing fertilization and to the enhanced NH3 volatilization under high temperature, respectively. A relatively large discrepancy between the inventories existed in the northern YRD with abundant croplands. With the estimated emissions 38 % smaller in E2, the average of simulated NH3 concentrations with an air quality model using E2 was 27 % smaller than that using E1 at two ground sites in the YRD. At the suburban site in Pudong, Shanghai (SHPD), the simulated NH3 concentrations with E1 were generally larger than observations, and the modeling performance was improved, indicated by the smaller normalized mean errors (NMEs) when E2 was applied. In contrast, very limited improvement was found at the urban site JSPAES, as E2 failed to improve the emission estimation of transportation and residential activities. Compared to NH3, the modeling performance for inorganic aerosols was better for most cases, and the differences between the simulated concentrations with E1 and E2 were clearly smaller, at 7 %, 3 %, and 12 % (relative to E1) for NH4+, SO42-, and NO3-, respectively. Compared to the satellite-derived NH3 column, application of E2 significantly corrected the overestimation in vertical column density for January and October with E1, but it did not improve the model performance for July. The NH3 emissions might be underestimated with the assumption of linear correlation between NH3 volatilization and soil pH for acidic soil, particularly in warm seasons. Three additional cases, i.e., 40 % abatement of SO2, 40 % abatement of NOx, and 40 % abatement of both species, were applied to test the sensitivity of NH3 and inorganic aerosol concentrations to precursor emissions. Under an NH3-rich condition, estimation of SO2 emissions was detected to be more effective on simulation of secondary inorganic aerosols compared to NH3. Reduced SO2 would restrain the formation of (NH4)2SO4 and thereby enhance the NH3 concentrations. To improve the air quality more effectively and efficiently, NH3 emissions should be substantially controlled along with SO2 and NOx in the future.
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Flizikowski, Adam, Marcin Przybyszewski und Witold Hołubowicz. „Evaluation of wimax admission control algorithms in mobile voip scenarios with batch arrivals and nbldpc fec“. Image Processing & Communications 18, Nr. 1 (01.03.2013): 45–56. http://dx.doi.org/10.2478/v10248-012-0072-5.
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Abstract This paper presents results of assessing quality of VoIP conversations in WiMAX networks using the nbLDPC (non-binary Low- Density Parity-Check) FEC in mobility scenarios that are based on the real world terrain charactristics around simulated BS. System under test (SUT) is instrumented with three Call Admission Control (CAC) mechanisms (namely EMAC, ARAC and nsc-ARAC). These algorithms are evaluated against controlling the VBR traffic that comes with burst arrivals. The first algorithm relies on calculating simple exponential weighted moving average (EWMA) of the overall resource consumption whereas the other two ARAC algorithms perform calculations discerning between the new, the ongoing and the finishing connections thus providing more accurate resource estimations (but the ARAC tracks the history of requests as well). In order to evaluate their performance authors rely on a cell-level based simulation environment that relies on the cooperative use of well known simulators - ns2 and Matlab. Previous work in the field is enhanced by improving the fidelity of proposed IEEE 802.16 simulator. Authors demonstrate the influence of increasing number of arrivals per one batch as well as testing the "zero hour" scenario (system saturation). In order to include nbLDPC codes in SUT’s mobile channels, a method called Link-To-System interface (L2S) has been implemented.
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Watson, Catherine J. „Preferential uptake of ammonium nitrogen from soil by ryegrass under simulated spring conditions“. Journal of Agricultural Science 107, Nr. 1 (August 1986): 171–77. http://dx.doi.org/10.1017/s0021859600066922.
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SUMMARYThe 15N isotope was used to compare the uptake and recovery of NH4 + and NO3 – nitrogen by ryegrass growing in soil under controlled simulated spring conditions when the temperature of the root was appreciably lower than that of the shoot. A preference was shown for NH4 + N over N03 – N, particularly at low soil temperatures. The limited uptake of NO3 – does not appear to be due to an inhibitory effect of the NH4 + ion. Ryegrass not only absorbed less N from NO3 – but also translocated a lower percentage of the total nitrogen taken up, to the shoots, the difference being greatest at low soil temperatures.The results give increasing support for the recommendation that early spring nitrogen should be applied in the NH4 + form. However, the preferential uptake and translocation of NH4 + ions would be of agricultural importance only if it led to an increase in dry-matter production.
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Appel, K. W., K. M. Foley, J. O. Bash, R. W. Pinder, R. L. Dennis, D. J. Allen und K. Pickering. „A multi-resolution assessment of the Community Multiscale Air Quality (CMAQ) model v4.7 wet deposition estimates for 2002–2006“. Geoscientific Model Development 4, Nr. 2 (03.05.2011): 357–71. http://dx.doi.org/10.5194/gmd-4-357-2011.
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Abstract. This paper examines the operational performance of the Community Multiscale Air Quality (CMAQ) model simulations for 2002–2006 using both 36-km and 12-km horizontal grid spacing, with a primary focus on the performance of the CMAQ model in predicting wet deposition of sulfate (SO4=), ammonium (NH4+) and nitrate (NO3−). Performance of the wet deposition estimates from the model is determined by comparing CMAQ predicted concentrations to concentrations measured by the National Acid Deposition Program (NADP), specifically the National Trends Network (NTN). For SO4= wet deposition, the CMAQ model estimates were generally comparable between the 36-km and 12-km simulations for the eastern US, with the 12-km simulation giving slightly higher estimates of SO4= wet deposition than the 36-km simulation on average. The result is a slightly larger normalized mean bias (NMB) for the 12-km simulation; however both simulations had annual biases that were less than ±15 % for each of the five years. The model estimated SO4= wet deposition values improved when they were adjusted to account for biases in the model estimated precipitation. The CMAQ model underestimates NH4+ wet deposition over the eastern US, with a slightly larger underestimation in the 36-km simulation. The largest underestimations occur in the winter and spring periods, while the summer and fall have slightly smaller underestimations of NH4+ wet deposition. The underestimation in NH4+ wet deposition is likely due in part to the poor temporal and spatial representation of ammonia (NH3) emissions, particularly those emissions associated with fertilizer applications and NH3 bi-directional exchange. The model performance for estimates of NO3− wet deposition are mixed throughout the year, with the model largely underestimating NO3− wet deposition in the spring and summer in the eastern US, while the model has a relatively small bias in the fall and winter. Model estimates of NO3− wet deposition tend to be slightly lower for the 36-km simulation as compared to the 12-km simulation, particularly in the spring. The underestimation of NO3− wet deposition in the spring and summer is due in part to a lack of lightning generated NO emissions in the upper troposphere, which can be a large source of NO in the spring and summer when lightning activity is the high. CMAQ model simulations that include production of NO from lightning show a significant improvement in the NO3− wet deposition estimates in the eastern US in the summer. Overall, performance for the 36-km and 12-km CMAQ model simulations is similar for the eastern US, while for the western US the performance of the 36-km simulation is generally not as good as either eastern US simulation, which is not entire unexpected given the complex topography in the western US.
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Appel, K. W., K. M. Foley, J. O. Bash, R. W. Pinder, R. L. Dennis, D. J. Allen und K. Pickering. „A multi-resolution assessment of the Community Multiscale Air Quality (CMAQ) Model v4.7 wet deposition estimates for 2002–2006“. Geoscientific Model Development Discussions 3, Nr. 4 (09.12.2010): 2315–60. http://dx.doi.org/10.5194/gmdd-3-2315-2010.
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Abstract. This paper examines the operational performance of the Community Multiscale Air Quality (CMAQ) model simulations for 2002–2006 using both 36-km and 12-km horizontal grid spacing with a primary focus on the performance of the CMAQ model in predicting wet deposition of sulfate (SO4=), ammonium (NH4+) and nitrate (NO3−). Performance of the wet deposition species is determined by comparing CMAQ predicted concentrations to concentrations measured by the National Acid Deposition Program (NADP), specifically the National Trends Network (NTN). For SO4= wet deposition, the CMAQ model estimates were generally comparable between the 36-km and 12-km simulations for the eastern US, with the 12-km simulation giving slightly higher estimates of SO4= wet deposition than the 36-km simulation on average. The normalized mean bias (NMB) was slightly higher for the 12-km simulation, however, both simulations had annual biases that were less than ±15% for each of the five years. The model estimated SO4= wet deposition values improved when they were adjusted to account for biases in the model estimated precipitation. The CMAQ model underestimates NH4+ wet deposition over the eastern US using both the 36-km and 12-km horizontal grid spacing, with a slightly larger underestimation in the 36-km simulation. The largest underestimations occur during the winter and spring periods, while the summer and fall have slightly smaller underestimations of NH4+ wet deposition. Annually, the NMB generally ranges between −10% and −16% for the 12-km simulation and −12% to −18% for the 36-km simulation over the five-year period for the eastern US. The underestimation in NH4+ wet deposition is likely due, in part, to the poor temporal and spatial representation of ammonia (NH3) emissions, particularly those emissions associated with fertilizer applications and NH3 bi-directional exchange. The model performance for estimates of NO3− wet deposition are mixed throughout the year, with the model largely underestimating NO3− wet deposition in the spring and summer in the eastern US, while the model has a relatively small bias in the fall and winter. Model estimates of NO3− wet deposition tend to be slightly lower for the 36-km simulation as compared to the 12-km simulation, particularly in the spring. Annually for the eastern US, the NMB ranges from roughly −12% to −20% for the 12-km simulation and −18% to −26% for the 36-km simulation. The underestimation of NO3− wet deposition in the spring and summer is due, in part, to a lack of lightning generated NO emissions in the upper troposphere, which can be a large source of NO in the spring and summer when lightning activity is the high. CMAQ model simulations that include the production of NO from lightning show a significant improvement in the NO3− wet deposition estimates in the eastern US in the summer. Model performance for the western US was generally not as good as that for the eastern US for all three wet deposition species.
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Wang, Meixin, Zhaoliang Peng, Changming Zhang, Mengmeng Liu, Lina Han, Yaqin Hou, Zhanggen Huang, Jiancheng Wang, Weiren Bao und Liping Chang. „Effect of Copper Precursors on the Activity and Hydrothermal Stability of CuII−SSZ−13 NH3−SCR Catalysts“. Catalysts 9, Nr. 9 (19.09.2019): 781. http://dx.doi.org/10.3390/catal9090781.
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A series of CuII−SSZ−13 catalysts are prepared by in-situ hydrothermal method using different copper precursors (CuII(NO3)2, CuIISO4, CuIICl2) for selective catalytic reduction of NO by NH3 in a simulated diesel vehicle exhaust. The catalysts were characterized by X−ray diffraction (XRD), scanning electron microscope (SEM), X−ray photoelectron spectroscopy (XPS), N2 adsorption-desorption, hydrogen-temperature-programmed reduction (H2−TPR), ammonia temperature-programmed desorption (NH3−TPD), and 27Al and 29Si solid state Nuclear Magnetic Resonance (NMR). The CuII−SSZ−13 catalyst prepared by CuII(NO3)2 shows excellent catalytic activity and hydrothermal stability. The NO conversion of CuII−SSZ−13 catalyst prepared by CuII(NO3)2 reaches 90% at 180 °C and can remain above 90% at a wide temperature range of 180–700 °C. After aging treatment at 800 °C for 20 h, the CuII−SSZ−13 catalyst prepared by CuII(NO3)2 still exhibits above 90% NO conversion under a temperature range of 240–600 °C. The distribution of Cu species and the Si/Al ratios in the framework of the synthesized CuII−SSZ−13 catalysts, which determine the catalytic activity and the hydrothermal stability of the catalysts, are dependent on the adsorption capacity of anions to the cation during the crystallization process due to the so called Hofmeister anion effects, the NO3− ion has the strongest adsorption capacity among the three kinds of anions (NO3−, Cl−, and SO42−), followed by Cl– and SO42– ions. Therefore, the CuII−SSZ−13 catalyst prepared by CuII(NO3)2 possess the best catalytic ability and hydrothermal stability.
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Lei, Junshan, Jiazhou Chen und Wei Yin. „Retention Efficiency of Vegetative Filter Strips for Nitrogen in Danjiangkou Reservoir Area, Central China“. Ecological Chemistry and Engineering S 26, Nr. 2 (01.06.2019): 279–97. http://dx.doi.org/10.1515/eces-2019-0020.
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Abstract To investigate the retention efficiency and mechanism of nitrogen of Vegetative filter strips (VFSs) in the Danjiangkou Reservoir area, simulated runoff discharging experiments were carried out in a new-established Bermuda VFS. The results showed that the Bermuda VFS reduced 73.1-86.1 % of surface runoff through infiltration. The outflow rate of runoff increased first and then became stable with time. The concentration reduction rates (CRRs) and load reduction rates (LRRs) of NH3-N increased initially and then decreased with the increase of inflow concentration. The average CRRs and LRRs of NH3-N in three treatments ranged 66.1-90.3 % and 90.0-96.7 %, respectively. The concentration reduction of NH3-N was primarily achieved by soil adsorption. The optimal inflow concentration of NH3-N for the optimum CRR was between 0.65 and 3.52 mg/dm3. The CRRs and LRRs of NO3-N fluctuated between 6.8-14.0 % and 72.0-77.9 % in three treatments. The concentration reduction of NO3-N was primarily achieved by plant uptake and soil microbe assimilation. The optimal inflow concentration of NO3-N for optimum CRR exceeded 6.78 mg/dm3. The CRRs and LRRs of TN increased with the increase of inflow concentrations. The average CRRs in the low, moderate and high treatments reached 9.7, 14.8 and 27.4 %, respectively, and the average LRRs reached 72.1, 74.3 and 81.2 %, respectively. The optimal inflow concentration of TN for optimum CRR exceeded 10.21 mg/dm3. The study showed that Bermuda grass can retain nitrogen in runoff efficiently and should be promoted around the Danjiangkou reservoir.
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Schürz, Christoph, Brigitta Hollosi, Christoph Matulla, Alexander Pressl, Thomas Ertl, Karsten Schulz und Bano Mehdi. „A comprehensive sensitivity and uncertainty analysis for discharge and nitrate-nitrogen loads involving multiple discrete model inputs under future changing conditions“. Hydrology and Earth System Sciences 23, Nr. 3 (04.03.2019): 1211–44. http://dx.doi.org/10.5194/hess-23-1211-2019.
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Abstract. Environmental modeling studies aim to infer the impacts on environmental variables that are caused by natural and human-induced changes in environmental systems. Changes in environmental systems are typically implemented as discrete scenarios in environmental models to simulate environmental variables under changing conditions. The scenario development of a model input usually involves several data sources and perhaps other models, which are potential sources of uncertainty. The setup and the parametrization of the implemented environmental model are additional sources of uncertainty for the simulation of environmental variables. Yet to draw well-informed conclusions from the model simulations it is essential to identify the dominant sources of uncertainty. In impact studies in two Austrian catchments the eco-hydrological model Soil and Water Assessment Tool (SWAT) was applied to simulate discharge and nitrate-nitrogen (NO3--N) loads under future changing conditions. For both catchments the SWAT model was set up with different spatial aggregations. Non-unique model parameter sets were identified that adequately reproduced observations of discharge and NO3--N loads. We developed scenarios of future changes for land use, point source emissions, and climate and implemented the scenario realizations in the different SWAT model setups with different model parametrizations, which resulted in 7000 combinations of scenarios and model setups for both catchments. With all model combinations we simulated daily discharge and NO3--N loads at the catchment outlets. The analysis of the 7000 generated model combinations of both case studies had two main goals: (i) to identify the dominant controls on the simulation of discharge and NO3--N loads in the two case studies and (ii) to assess how the considered inputs control the simulation of discharge and NO3--N loads. To assess the impact of the input scenarios, the model setup, and the parametrization on the simulation of discharge and NO3--N loads, we employed methods of global sensitivity analysis (GSA). The uncertainties in the simulation of discharge and NO3--N loads that resulted from the 7000 SWAT model combinations were evaluated visually. We present approaches for the visualization of the simulation uncertainties that support the diagnosis of how the analyzed inputs affected the simulation of discharge and NO3--N loads. Based on the GSA we identified climate change and the model parametrization as being the most influential model inputs for the simulation of discharge and NO3--N loads in both case studies. In contrast, the impact of the model setup on the simulation of discharge and NO3--N loads was low, and the changes in land use and point source emissions were found to have the lowest impact on the simulated discharge and NO3--N loads. The visual analysis of the uncertainty bands illustrated that the deviations in precipitation of the different climate scenarios to historic records dominated the changes in simulation outputs, while the differences in air temperature showed no considerable impact.
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Han, Wen Zhi. „Network Congestion Control Algorithm Simulation Research Based on NS2“. Applied Mechanics and Materials 713-715 (Januar 2015): 2455–61. http://dx.doi.org/10.4028/www.scientific.net/amm.713-715.2455.
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Network congestion control problem is one of the most key problems in network study. This paper studies different versions of TCP source port algorithm such as Tahoe, Reno, NewReno, SACK and Vegas, and makes simulation research on linear network and dumbbell network environment algorithm by using NS2 network simulator, and finally it concludes that: when there is no competition in the network, it is better to choose Vegas algorithm; when there is competition, choose Reno, NewReno, or Sack algorithm is more advisable.
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Xing, J., R. Mathur, J. Pleim, C. Hogrefe, C. M. Gan, D. C. Wong, C. Wei, R. Gilliam und G. Pouliot. „Observations and modeling of air quality trends over 1990–2010 across the Northern Hemisphere: China, the United States and Europe“. Atmospheric Chemistry and Physics Discussions 14, Nr. 18 (08.10.2014): 25453–501. http://dx.doi.org/10.5194/acpd-14-25453-2014.
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Abstract. Trends in air quality across the Northern Hemisphere over a 21 year period (1990–2010) were simulated using the CMAQ multiscale chemical transport model driven by meteorology from WRF simulations and internally consistent historical emission inventories obtained from EDGAR. Thorough comparison with several ground observation networks mostly over Europe and North America was conducted to evaluate the model performance as well as the ability of CMAQ to reproduce the observed trends in air quality over the past two decades in three regions: eastern China, the continental United States and Europe. The model successfully reproduced the observed decreasing trends in SO2, NO2, maxima 8 h O3, SO42− and EC in the US and Europe. However, the model fails to reproduce the decreasing trends in NO3− in the US, potentially pointing to uncertainties of NH3 emissions. The model failed to capture the 6 year trends of SO2 and NO2 in CN-API from 2005–2010, but reproduced the observed pattern of O3 trends shown in three WDCGG sites over eastern Asia. Due to the coarse spatial resolution employed in these calculations, predicted SO2 and NO2 concentrations are underestimated relative to all urban networks, i.e., US-AQS (NMB = −46 and −54%), EU-AIRBASE (NMB = −12 and −57%) and CN-API (NMB = −36 and −68%). Conversely, at the rural network EU-EMEP SO2 is overestimated (NMB from 4 to 150%) while NO2 is simulated well (NMB within ±15%) in all seasons. Correlations between simulated and observed winter time daily maxima 8 h (DM8) O3 are poor compared to other seasons for all networks. Better correlation between simulated and observed SO42− was found compared to that for SO2. Underestimation of summer SO42− in the US may be associated with the uncertainty in precipitation and associated wet scavenging representation in the model. The model exhibits worse performance for NO3− predictions, particularly in summer, due to high uncertainties in the gas/particle partitioning of NO3− as well as seasonal variations of NH3 emissions. There are high correlations (R > 0.5) between observed and simulated EC, although the model underestimates the EC concentration by 65% due to the coarse grid resolution as well as uncertainties in the PM speciation profile associated with EC emissions. The almost linear response seen in the trajectory of modeled O3 changes in the eastern China over the past two decades, suggests that control strategies that focus on combined control of NOx and VOC emissions with a ratio of 0.46 may provide the most effective means for O3 reductions for the region devoid of non-linear response potentially associated with NOx or VOC limitation resulting from alternate strategies. The response of O3 is more sensitive to changes in NOx emissions in the eastern US because the relative abundance of biogenic VOC emissions tends to reduce the effectiveness of VOC controls. Increasing NH3 levels offset the relative effectiveness of NOx controls in reducing the relative fraction of aerosol NO3− formed from declining NOx emissions in the eastern US, while the control effectiveness was assured by the simultaneous control of NH3 emission in Europe.
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Tagaris, E., R. E. P. Sotiropoulou, N. Gounaris, S. Andronopoulos und D. Vlachogiannis. „Air quality over Europe: modelling gaseous and particulate pollutants“. Atmospheric Chemistry and Physics 13, Nr. 18 (30.09.2013): 9661–73. http://dx.doi.org/10.5194/acp-13-9661-2013.
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Abstract. Air quality over Europe using Models-3 (i.e., CMAQ, MM5, SMOKE) modelling system is performed for winter (i.e., January 2006) and summer (i.e., July 2006) months with the 2006 TNO gridded anthropogenic emissions database. Higher ozone mixing ratios are predicted in southern Europe while higher NO2 levels are simulated over western Europe. Elevated SO2 values are simulated over eastern Europe and higher PM2.5 concentrations over eastern and western Europe. Regional average results suggest that NO2 and PM2.5 are underpredicted, SO2 is overpredicted, while Max8hrO3 is overpredicted for low mixing ratios and is underpredicted for the higher mixing ratios. However, in a number of countries observed and predicted values are in good agreement for the pollutants examined here. Speciated PM2.5 components suggest that NO3 is dominant during winter over western Europe and in a few eastern countries due to the high NO2 mixing ratios. During summer NO3 is dominant only in regions with elevated NH3 emissions. For the rest of the domain SO4 is dominant. Low OC concentrations are simulated mainly due to the uncertain representation of SOA formation.
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Zamani, Elham, und Mohammadreza Soltanaghaei. „The Improved Overhearing Backup AODV Protocol in MANET“. Journal of Computer Networks and Communications 2016 (2016): 1–8. http://dx.doi.org/10.1155/2016/6463157.
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Mobile ad hoc network (MANET) is one of the most widely used networks, which has attracted attentions, having features such as limited energy resources, limited bandwidth, and security weaknesses due to lack of a central infrastructure. Safe and suitable routing is one of the research aspects of MANET. In this paper, a proposed method, called M-AODV, which is a type of overhearing backup protocol, based on AODV, is presented. The simulation results of this protocol, applied by NS2 simulator, showed the improvement of packet delivery rate and reduction of overhead and delay. Moreover, to assess the security of the proposed protocol, we simulated M-AODV and AODV protocols under black hole and wormhole attacks, using no security solution. The results showed that M-AODV had been improved in terms of packet delivery ratio, and the delay had been reduced as well, but the amount of overhead had been increased.
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Dave, Heena H., Prof Parul Dihulia und Prof Vikas Gupta. „Performance Analysis by Varying Parameters of TCP Variants Using NS-2 Simulator“. International Journal of Scientific Research 2, Nr. 4 (01.06.2012): 124–27. http://dx.doi.org/10.15373/22778179/apr2013/45.
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Chen, Lei, Yi Gao, Meigen Zhang, Joshua S. Fu, Jia Zhu, Hong Liao, Jialin Li et al. „MICS-Asia III: multi-model comparison and evaluation of aerosol over East Asia“. Atmospheric Chemistry and Physics 19, Nr. 18 (25.09.2019): 11911–37. http://dx.doi.org/10.5194/acp-19-11911-2019.
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Abstract. A total of 14 chemical transport models (CTMs) participated in the first topic of the Model Inter-Comparison Study for Asia (MICS-Asia) phase III. These model results are compared with each other and an extensive set of measurements, aiming to evaluate the current CTMs' ability in simulating aerosol concentrations, to document the similarities and differences among model performance, and to reveal the characteristics of aerosol components in large cities over East Asia. In general, these CTMs can well reproduce the spatial–temporal distributions of aerosols in East Asia during the year 2010. The multi-model ensemble mean (MMEM) shows better performance than most single-model predictions, with correlation coefficients (between MMEM and measurements) ranging from 0.65 (nitrate, NO3-) to 0.83 (PM2.5). The concentrations of black carbon (BC), sulfate (SO42-), and PM10 are underestimated by MMEM, with normalized mean biases (NMBs) of −17.0 %, −19.1 %, and −32.6 %, respectively. Positive biases are simulated for NO3- (NMB = 4.9 %), ammonium (NH4+) (NMB = 14.0 %), and PM2.5 (NMB = 4.4 %). In comparison with the statistics calculated from MICS-Asia phase II, frequent updates of chemical mechanisms in CTMs during recent years make the intermodel variability of simulated aerosol concentrations smaller, and better performance can be found in reproducing the temporal variations of observations. However, a large variation (about a factor of 2) in the ratios of SNA (sulfate, nitrate, and ammonium) to PM2.5 is calculated among participant models. A more intense secondary formation of SO42- is simulated by Community Multi-scale Air Quality (CMAQ) models, because of the higher SOR (sulfur oxidation ratio) than other models (0.51 versus 0.39). The NOR (nitric oxidation ratio) calculated by all CTMs has larger values (∼0.20) than the observations, indicating that overmuch NO3- is simulated by current models. NH3-limited condition (the mole ratio of ammonium to sulfate and nitrate is smaller than 1) can be successfully reproduced by all participant models, which indicates that a small reduction in ammonia may improve the air quality. A large coefficient of variation (CV > 1.0) is calculated for simulated coarse particles, especially over arid and semi-arid regions, which means that current CTMs have difficulty producing similar dust emissions by using different dust schemes. According to the simulation results of MMEM in six large Asian cities, different air-pollution control plans should be taken due to their different major air pollutants in different seasons. The MICS-Asia project gives an opportunity to discuss the similarities and differences of simulation results among CTMs in East Asian applications. In order to acquire a better understanding of aerosol properties and their impacts, more experiments should be designed to reduce the diversities among air quality models.
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Balogh, Tomáš, und Martin Medvecký. „Average Bandwidth Allocation Model of WFQ“. Modelling and Simulation in Engineering 2012 (2012): 1–7. http://dx.doi.org/10.1155/2012/301012.
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We present a new iterative method for the calculation of average bandwidth assignment to traffic flows using a WFQ scheduler in IP based NGN networks. The bandwidth assignment calculation is based on the link speed, assigned weights, arrival rate, and average packet length or input rate of the traffic flows. We prove the model outcome with examples and simulation results using NS2 simulator.
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Xing, J., R. Mathur, J. Pleim, C. Hogrefe, C. M. Gan, D. C. Wong, C. Wei, R. Gilliam und G. Pouliot. „Observations and modeling of air quality trends over 1990–2010 across the Northern Hemisphere: China, the United States and Europe“. Atmospheric Chemistry and Physics 15, Nr. 5 (10.03.2015): 2723–47. http://dx.doi.org/10.5194/acp-15-2723-2015.
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Abstract. Trends in air quality across the Northern Hemisphere over a 21-year period (1990–2010) were simulated using the Community Multiscale Air Quality (CMAQ) multiscale chemical transport model driven by meteorology from Weather Research and Forecasting (WRF) simulations and internally consistent historical emission inventories obtained from EDGAR. Thorough comparison with several ground observation networks mostly over Europe and North America was conducted to evaluate the model performance as well as the ability of CMAQ to reproduce the observed trends in air quality over the past 2 decades in three regions: eastern China, the continental United States and Europe. The model successfully reproduced the observed decreasing trends in SO2, NO2, 8 h O3 maxima, SO42− and elemental carbon (EC) in the US and Europe. However, the model fails to reproduce the decreasing trends in NO3− in the US, potentially pointing to uncertainties of NH3 emissions. The model failed to capture the 6-year trends of SO2 and NO2 in CN-API (China – Air Pollution Index) from 2005 to 2010, but reproduced the observed pattern of O3 trends shown in three World Data Centre for Greenhouse Gases (WDCGG) sites over eastern Asia. Due to the coarse spatial resolution employed in these calculations, predicted SO2 and NO2 concentrations are underestimated relative to all urban networks, i.e., US-AQS (US – Air Quality System; normalized mean bias (NMB) = −38% and −48%), EU-AIRBASE (European Air quality data Base; NMB = −18 and −54%) and CN-API (NMB = −36 and −68%). Conversely, at the rural network EU-EMEP (European Monitoring and Evaluation Programme), SO2 is overestimated (NMB from 4 to 150%) while NO2 is simulated well (NMB within ±15%) in all seasons. Correlations between simulated and observed O3 wintertime daily 8 h maxima (DM8) are poor compared to other seasons for all networks. Better correlation between simulated and observed SO42− was found compared to that for SO2. Underestimation of summer SO42− in the US may be associated with the uncertainty in precipitation and associated wet scavenging representation in the model. The model exhibits worse performance for NO3− predictions, particularly in summer, due to high uncertainties in the gas/particle partitioning of NO3− as well as seasonal variations of NH3 emissions. There are high correlations (R > 0.5) between observed and simulated EC, although the model underestimates the EC concentration by 65% due to the coarse grid resolution as well as uncertainties in the PM speciation profile associated with EC emissions. The almost linear response seen in the trajectory of modeled O3 changes in eastern China over the past 2 decades suggests that control strategies that focus on combined control of NOx and volatile organic compound (VOC) emissions with a ratio of 0.46 may provide the most effective means for O3 reductions for the region devoid of nonlinear response potentially associated with NOx or VOC limitation resulting from alternate strategies. The response of O3 is more sensitive to changes in NOx emissions in the eastern US because the relative abundance of biogenic VOC emissions tends to reduce the effectiveness of VOC controls. Increasing NH3 levels offset the relative effectiveness of NOx controls in reducing the relative fraction of aerosol NO3− formed from declining NOx emissions in the eastern US, while the control effectiveness was assured by the simultaneous control of NH3 emission in Europe.
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Kim, Hye-Sun, und Ki-Tae Hwang. „NS2 based Simulator for Performance Evaluation of P2P Streaming Systems“. KIPS Transactions:PartD 14D, Nr. 5 (31.08.2007): 555–64. http://dx.doi.org/10.3745/kipstd.2007.14-d.5.555.
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