The grassland of Qinghai-Tibet Plateau (QTP) and Inner Mongolia Plateau (IMP), accounting for 73.9% of the total grassland area in China, is significant to food and ecological safety. Due to climate change and irratio...The grassland of Qinghai-Tibet Plateau (QTP) and Inner Mongolia Plateau (IMP), accounting for 73.9% of the total grassland area in China, is significant to food and ecological safety. Due to climate change and irrational human activities, grasslands on the two plateaus have severely degraded over recent decades. Understanding the dynamic changes of grassland and its driving forces is necessary to make effective measurements to prevent grassland degradation. Here, we selected the net primary productivity (NPP) as an indicator to quantitatively assess the dynamic variation of grassland and the relative roles of climate change and human activities on QTP and IMP from 2000 to 2016. The results found significant spatial variability of grassland on QTP. 28.3% of the grassland experienced degradation and was mainly distributed in the southern QTP, versus 71.7% of the grassland was restored and mainly distributed in the central and northern QTP. In contrast, grassland on IMP didn’t show significant spatial variability. Most of the grassland on IMP was restored during the study period. Climate change (i.e. increased precipitation) was the dominant factor and could explain 72.8% and 84.4% of the restored grassland in QTP and IMP. Irrational human activities (i.e. overgrazing) were the main driving factors and could explain 72.9% and 100.0% of the degraded grassland on the two plateaus during the study period. Ecological restoration projects were favorable for grassland restoration on the two plateaus, and they contributed to 27.2% and 15.6% of the restored grassland in QTP and IMP, respectively. Therefore, climate changes on IMP were more favorable for grassland restoration, and human activities have a greater impact on the grassland variation on QTP.展开更多
With the widespread application of wireless communication technology and continuous improvements to Internet of Things(IoT)technology,fog computing architecture composed of edge,fog,and cloud layers have become a rese...With the widespread application of wireless communication technology and continuous improvements to Internet of Things(IoT)technology,fog computing architecture composed of edge,fog,and cloud layers have become a research hotspot.This architecture uses Fog Nodes(FNs)close to users to implement certain cloud functions while compensating for cloud disadvantages.However,because of the limited computing and storage capabilities of a single FN,it is necessary to offload tasks to multiple cooperating FNs for task completion.To effectively and quickly realize task offloading,we use network calculus theory to establish an overall performance model for task offloading in a fog computing environment and propose a Globally Optimal Multi-objective Optimization algorithm for Task Offloading(GOMOTO)based on the performance model.The results show that the proposed model and algorithm can effectively reduce the total delay and total energy consumption of the system and improve the network Quality of Service(QoS).展开更多
Software-defined networks (SDN) have attracted much attention recently because of their flexibility in terms of network management. Increasingly, SDN is being introduced into wireless networks to form wireless SDN. ...Software-defined networks (SDN) have attracted much attention recently because of their flexibility in terms of network management. Increasingly, SDN is being introduced into wireless networks to form wireless SDN. One enabling technology for wireless SDN is network virtualization, which logically divides one wireless network element, such as a base station, into multiple slices, and each slice serving as a standalone virtual BS. In this way, one physical mobile wireless network can be partitioned into multiple virtual networks in a software-defined manner. Wireless virtual networks comprising virtual base stations also need to provide QoS to mobile end-user services in the same context as their physical hosting networks. One key QoS parameter is delay. This paper presents a delay model for software-defined wireless virtual networks. Network calculus is used in the modelling. In particular, stochastic network calculus, which describes more realistic models than deterministic network calculus, is used. The model enables theoretical investigation of wireless SDN, which is largely dominated by either algorithms or prototype implementations.展开更多
Edge computing can alleviate the problem of insufficient computational resources for the user equipment,improve the network processing environment,and promote the user experience.Edge computing is well known as a pros...Edge computing can alleviate the problem of insufficient computational resources for the user equipment,improve the network processing environment,and promote the user experience.Edge computing is well known as a prospective method for the development of the Internet of Things(IoT).However,with the development of smart terminals,much more time is required for scheduling the terminal high-intensity upstream dataflow in the edge server than for scheduling that in the downstream dataflow.In this paper,we study the scheduling strategy for upstream dataflows in edge computing networks and introduce a three-tier edge computing network architecture.We propose a Time-Slicing Self-Adaptive Scheduling(TSAS)algorithm based on the hierarchical queue,which can reduce the queuing delay of the dataflow,improve the timeliness of dataflow processing and achieve an efficient and reasonable performance of dataflow scheduling.The experimental results show that the TSAS algorithm can reduce latency,minimize energy consumption,and increase system throughput.展开更多
文摘The grassland of Qinghai-Tibet Plateau (QTP) and Inner Mongolia Plateau (IMP), accounting for 73.9% of the total grassland area in China, is significant to food and ecological safety. Due to climate change and irrational human activities, grasslands on the two plateaus have severely degraded over recent decades. Understanding the dynamic changes of grassland and its driving forces is necessary to make effective measurements to prevent grassland degradation. Here, we selected the net primary productivity (NPP) as an indicator to quantitatively assess the dynamic variation of grassland and the relative roles of climate change and human activities on QTP and IMP from 2000 to 2016. The results found significant spatial variability of grassland on QTP. 28.3% of the grassland experienced degradation and was mainly distributed in the southern QTP, versus 71.7% of the grassland was restored and mainly distributed in the central and northern QTP. In contrast, grassland on IMP didn’t show significant spatial variability. Most of the grassland on IMP was restored during the study period. Climate change (i.e. increased precipitation) was the dominant factor and could explain 72.8% and 84.4% of the restored grassland in QTP and IMP. Irrational human activities (i.e. overgrazing) were the main driving factors and could explain 72.9% and 100.0% of the degraded grassland on the two plateaus during the study period. Ecological restoration projects were favorable for grassland restoration on the two plateaus, and they contributed to 27.2% and 15.6% of the restored grassland in QTP and IMP, respectively. Therefore, climate changes on IMP were more favorable for grassland restoration, and human activities have a greater impact on the grassland variation on QTP.
基金This work was supported in part by the Natural Science Foundation of China(Nos.61572191 and 61602171)the Natural Science Foundation of Hunan Province,China(Nos.2022JJ30398 and 2021JJ30455).
文摘With the widespread application of wireless communication technology and continuous improvements to Internet of Things(IoT)technology,fog computing architecture composed of edge,fog,and cloud layers have become a research hotspot.This architecture uses Fog Nodes(FNs)close to users to implement certain cloud functions while compensating for cloud disadvantages.However,because of the limited computing and storage capabilities of a single FN,it is necessary to offload tasks to multiple cooperating FNs for task completion.To effectively and quickly realize task offloading,we use network calculus theory to establish an overall performance model for task offloading in a fog computing environment and propose a Globally Optimal Multi-objective Optimization algorithm for Task Offloading(GOMOTO)based on the performance model.The results show that the proposed model and algorithm can effectively reduce the total delay and total energy consumption of the system and improve the network Quality of Service(QoS).
基金supported in part by the grant from the National Natural Science Foundation of China (60973129)
文摘Software-defined networks (SDN) have attracted much attention recently because of their flexibility in terms of network management. Increasingly, SDN is being introduced into wireless networks to form wireless SDN. One enabling technology for wireless SDN is network virtualization, which logically divides one wireless network element, such as a base station, into multiple slices, and each slice serving as a standalone virtual BS. In this way, one physical mobile wireless network can be partitioned into multiple virtual networks in a software-defined manner. Wireless virtual networks comprising virtual base stations also need to provide QoS to mobile end-user services in the same context as their physical hosting networks. One key QoS parameter is delay. This paper presents a delay model for software-defined wireless virtual networks. Network calculus is used in the modelling. In particular, stochastic network calculus, which describes more realistic models than deterministic network calculus, is used. The model enables theoretical investigation of wireless SDN, which is largely dominated by either algorithms or prototype implementations.
基金This work were supported in part by the National Natural Science Foundation of China(No.61572191)Natural Science Foundation of Hunan Province(Nos.2022JJ30398,2022JJ40277 and 2022JJ40278)Scientific Research Fund of Hunan Provincial Education Department(No.17A130).
文摘Edge computing can alleviate the problem of insufficient computational resources for the user equipment,improve the network processing environment,and promote the user experience.Edge computing is well known as a prospective method for the development of the Internet of Things(IoT).However,with the development of smart terminals,much more time is required for scheduling the terminal high-intensity upstream dataflow in the edge server than for scheduling that in the downstream dataflow.In this paper,we study the scheduling strategy for upstream dataflows in edge computing networks and introduce a three-tier edge computing network architecture.We propose a Time-Slicing Self-Adaptive Scheduling(TSAS)algorithm based on the hierarchical queue,which can reduce the queuing delay of the dataflow,improve the timeliness of dataflow processing and achieve an efficient and reasonable performance of dataflow scheduling.The experimental results show that the TSAS algorithm can reduce latency,minimize energy consumption,and increase system throughput.