针对分布式电源(distributed generation,DG)接入配电网的特点提出两级实时重构的概念。两级实时重构是指正常运行方式下的最大概率重构(maximum probability reconfiguration,MPR),以及当DG出力或者负荷出现较大波动时,网络拓扑快速响...针对分布式电源(distributed generation,DG)接入配电网的特点提出两级实时重构的概念。两级实时重构是指正常运行方式下的最大概率重构(maximum probability reconfiguration,MPR),以及当DG出力或者负荷出现较大波动时,网络拓扑快速响应为实时重构(r e a l-t i m ereconfiguration,RTR)的运行方式。所提两级实时重构模型及方法重点考虑了DG出力和负荷的时变性、负荷的静态电压特性以及配电网的三相不平衡特性。文中比较了4种配电网重构方式的网损和网损率:始终维持原始拓扑结构、15 min实时重构、两级实时重构以及系统在额定负荷和额定DG出力水平下的最优重构。改进的IEEE 16节点和IEEE 34节点配电系统的仿真分析表明,所提的两级实时重构方法不仅能有效降低系统网损,同时提高了系统运行的安全性和可靠性。展开更多
The aim of this paper is to present DCM+, a new congestion control protocol for data networks. It stands for Dynamic Congestion control for Mobile networks. New metrics have been newly invented and introduced like nor...The aim of this paper is to present DCM+, a new congestion control protocol for data networks. It stands for Dynamic Congestion control for Mobile networks. New metrics have been newly invented and introduced like normalized advancing index (NAI) and complete transmission time (CTT). The simulations are done for a simple single-hop-topology (sender-router-receiver). The outcomes of this protocol are excellent and, in most cases, better than other approaches. The excellent properties of our proposed protocol were possible through tracking the available slow-start threshold. We achieved performance improvement, minimized end-to-end delay and large reduction in transmission time. DCM+ was able to combine many advantages at same time of the protocols NewReno and Westwood+. The results show, that DCM+ is extremely adequate for different types of networks. Feedback as main principle of control theory was used to control the congestion in the network. The parameters Round-Trip-Time (RTT) and Retransmission Timeout (RTO) are used as feedback signals to adjust the next congestion window (cwnd).展开更多
General purpose processer （GPP） based software-defined radio （SDR） platforms provide wireless communication system engineers with maximal architecture flexibility and versatility to construct a wideband wireless c...General purpose processer （GPP） based software-defined radio （SDR） platforms provide wireless communication system engineers with maximal architecture flexibility and versatility to construct a wideband wireless communication system. Nevertheless, the lack of hardware real-time timing control makes it difficult to achieve time synchronization between the base station and the terminals. In this paper, a software-based time synchronization （STS） method is proposed to realize the time synchronization of time division multiple access （TDMA） based wireless communication systems. A high precision software clock source is firstly constructed to measure the elapse of processing time. The Round-Trip Delay （RTD） algorithm is then presented to calculate timing advance values and achieve time synchronization. An example TDMA system is implemented on Microsoft Sora platforms to evaluate is effective to enable time synchronization for wideband the performance. Experiments show that the proposed mechanism wireless communication systems on GPP-based SDR platforms.展开更多
介绍用平板探测器的数字射线照相(DR)技术和用柔性荧光体成像板的计算机射线照相(CR)技术,对锅炉类承压设备受压元件的对接焊缝进行射线实时成像(RTR)检测和质量评价的最新国际动态和应用现状,并与常规胶片射线照相作了比较。实验结果表...介绍用平板探测器的数字射线照相(DR)技术和用柔性荧光体成像板的计算机射线照相(CR)技术,对锅炉类承压设备受压元件的对接焊缝进行射线实时成像(RTR)检测和质量评价的最新国际动态和应用现状,并与常规胶片射线照相作了比较。实验结果表明:DR可有效取代图像增强器式射线实时成像,检测的锅炉管焊缝单壁厚度可达12mm。用像素间距200μm的平板探测器,当调制传递函数MTF>20%时,可获分辨率优于3线对/mm。CR技术不仅适用于薄板和中厚板焊缝的射线照相检测,还适于板厚100mm以上大厚度锅炉压力容器和压力管道受压元件的检测,射线源从常规的400kV以下的X射线机到直线加速器(≤6M eV),从Ir192到Co60同位素源均可使用,空间分辨率≤25μm,能满足A SM E法规规定的2%的射线照相灵敏度要求。展开更多
To slove the problem that the implementation of Transmission Control Protocol (TCP) Vegas does not consider the impact of TCP's segment size on Round-Trip Time (RTT) while calculating RTT and the smallest RTT (bas...To slove the problem that the implementation of Transmission Control Protocol (TCP) Vegas does not consider the impact of TCP's segment size on Round-Trip Time (RTT) while calculating RTT and the smallest RTT (base _rtt), this paper proposes a modified congestion control mechanism for TCP Vegas. It first groups segments on the basis of segments size and updates base _rtt based on groups. In congestion avoidance phase, TCP Vegas changes its window size according to the measured RTT of the segment corresponding to the latest received ACK and the base _rtt retrieved from the group that the segment belongs to. Simulations illustrate that the enhanced TCP Vegas can achieve higher throughput up to 40 percent.展开更多
An effective method to detect stepping-stone intrusion(SSI)is to estimate the length of a connection chain.This type of detection method is referred to as a network-based detection approach.Existing network-based SSI ...An effective method to detect stepping-stone intrusion(SSI)is to estimate the length of a connection chain.This type of detection method is referred to as a network-based detection approach.Existing network-based SSI detection methods are either ineffective in the context of the Internet because of the presence of outliers in the packet round-trip times(RTTs)or inefficient,as many packets must be captured and processed.Because of the high fluctuation caused by the intermediate routers on the Internet,it is unavoidable that the RTTs of the captured packets contain outlier values.In this paper,we first propose an efficient algorithm to eliminate most of the possible RTT outliers of the packets captured in the Internet environment.We then develop an efficient SSI detection algorithm by mining network traffic using an improved version of k-Means clustering.Our proposed detection algorithm for SSI is accurate,effective,and efficient in the context of the Internet.Well-designed network experiments are conducted in the Internet environment to verify the effectiveness,correctness,and efficiency of our proposed algorithms.Our experiments show that the effective rate of our proposed SSI detection algorithm is higher than 85.7%in the context of the Internet.展开更多
Active queue management(AQM)is essential to prevent the degradation of quality of service in TCP/AQM systems with round-trip time(RTT)delay.RTT delays are primarily caused by packet-propagation delays,but they can als...Active queue management(AQM)is essential to prevent the degradation of quality of service in TCP/AQM systems with round-trip time(RTT)delay.RTT delays are primarily caused by packet-propagation delays,but they can also be caused by the processing time of queuing operations and dynamically changing network situations.This study focuses on the design and analysis of an AQM digital controller under time-delay uncertainty.The controller is based on the Smith predictor algorithm and is called the SMITHPI controller.This study also demonstrates the stability of the controller and its robustness against network parameter variations such as the number of TCP connections,time delays,and user datagram protocol flows.The performance,robustness,and effectiveness of the proposed SMITHPI controller are evaluated using the NS-2 simulator.Finally,the performance of the SMITHPI controller is compared with that of a well-known queue-based AQM,called the proportional-integral controller.展开更多
文摘针对分布式电源(distributed generation,DG)接入配电网的特点提出两级实时重构的概念。两级实时重构是指正常运行方式下的最大概率重构(maximum probability reconfiguration,MPR),以及当DG出力或者负荷出现较大波动时,网络拓扑快速响应为实时重构(r e a l-t i m ereconfiguration,RTR)的运行方式。所提两级实时重构模型及方法重点考虑了DG出力和负荷的时变性、负荷的静态电压特性以及配电网的三相不平衡特性。文中比较了4种配电网重构方式的网损和网损率:始终维持原始拓扑结构、15 min实时重构、两级实时重构以及系统在额定负荷和额定DG出力水平下的最优重构。改进的IEEE 16节点和IEEE 34节点配电系统的仿真分析表明,所提的两级实时重构方法不仅能有效降低系统网损,同时提高了系统运行的安全性和可靠性。
文摘The aim of this paper is to present DCM+, a new congestion control protocol for data networks. It stands for Dynamic Congestion control for Mobile networks. New metrics have been newly invented and introduced like normalized advancing index (NAI) and complete transmission time (CTT). The simulations are done for a simple single-hop-topology (sender-router-receiver). The outcomes of this protocol are excellent and, in most cases, better than other approaches. The excellent properties of our proposed protocol were possible through tracking the available slow-start threshold. We achieved performance improvement, minimized end-to-end delay and large reduction in transmission time. DCM+ was able to combine many advantages at same time of the protocols NewReno and Westwood+. The results show, that DCM+ is extremely adequate for different types of networks. Feedback as main principle of control theory was used to control the congestion in the network. The parameters Round-Trip-Time (RTT) and Retransmission Timeout (RTO) are used as feedback signals to adjust the next congestion window (cwnd).
基金Supported by the Major Project of Beijing Municipal Natural Science Foundation of China under Grant No. 4110001
文摘General purpose processer （GPP） based software-defined radio （SDR） platforms provide wireless communication system engineers with maximal architecture flexibility and versatility to construct a wideband wireless communication system. Nevertheless, the lack of hardware real-time timing control makes it difficult to achieve time synchronization between the base station and the terminals. In this paper, a software-based time synchronization （STS） method is proposed to realize the time synchronization of time division multiple access （TDMA） based wireless communication systems. A high precision software clock source is firstly constructed to measure the elapse of processing time. The Round-Trip Delay （RTD） algorithm is then presented to calculate timing advance values and achieve time synchronization. An example TDMA system is implemented on Microsoft Sora platforms to evaluate is effective to enable time synchronization for wideband the performance. Experiments show that the proposed mechanism wireless communication systems on GPP-based SDR platforms.
文摘介绍用平板探测器的数字射线照相(DR)技术和用柔性荧光体成像板的计算机射线照相(CR)技术,对锅炉类承压设备受压元件的对接焊缝进行射线实时成像(RTR)检测和质量评价的最新国际动态和应用现状,并与常规胶片射线照相作了比较。实验结果表明:DR可有效取代图像增强器式射线实时成像,检测的锅炉管焊缝单壁厚度可达12mm。用像素间距200μm的平板探测器,当调制传递函数MTF>20%时,可获分辨率优于3线对/mm。CR技术不仅适用于薄板和中厚板焊缝的射线照相检测,还适于板厚100mm以上大厚度锅炉压力容器和压力管道受压元件的检测,射线源从常规的400kV以下的X射线机到直线加速器(≤6M eV),从Ir192到Co60同位素源均可使用,空间分辨率≤25μm,能满足A SM E法规规定的2%的射线照相灵敏度要求。
文摘To slove the problem that the implementation of Transmission Control Protocol (TCP) Vegas does not consider the impact of TCP's segment size on Round-Trip Time (RTT) while calculating RTT and the smallest RTT (base _rtt), this paper proposes a modified congestion control mechanism for TCP Vegas. It first groups segments on the basis of segments size and updates base _rtt based on groups. In congestion avoidance phase, TCP Vegas changes its window size according to the measured RTT of the segment corresponding to the latest received ACK and the base _rtt retrieved from the group that the segment belongs to. Simulations illustrate that the enhanced TCP Vegas can achieve higher throughput up to 40 percent.
基金supported by the the National Centers of Academic Excellence in Cybersecurity(NCAE-C)Grant(No.H98230-20-1-0293)at the National Security Agency with Columbus State University,Georgia,USA。
文摘An effective method to detect stepping-stone intrusion(SSI)is to estimate the length of a connection chain.This type of detection method is referred to as a network-based detection approach.Existing network-based SSI detection methods are either ineffective in the context of the Internet because of the presence of outliers in the packet round-trip times(RTTs)or inefficient,as many packets must be captured and processed.Because of the high fluctuation caused by the intermediate routers on the Internet,it is unavoidable that the RTTs of the captured packets contain outlier values.In this paper,we first propose an efficient algorithm to eliminate most of the possible RTT outliers of the packets captured in the Internet environment.We then develop an efficient SSI detection algorithm by mining network traffic using an improved version of k-Means clustering.Our proposed detection algorithm for SSI is accurate,effective,and efficient in the context of the Internet.Well-designed network experiments are conducted in the Internet environment to verify the effectiveness,correctness,and efficiency of our proposed algorithms.Our experiments show that the effective rate of our proposed SSI detection algorithm is higher than 85.7%in the context of the Internet.
文摘Active queue management(AQM)is essential to prevent the degradation of quality of service in TCP/AQM systems with round-trip time(RTT)delay.RTT delays are primarily caused by packet-propagation delays,but they can also be caused by the processing time of queuing operations and dynamically changing network situations.This study focuses on the design and analysis of an AQM digital controller under time-delay uncertainty.The controller is based on the Smith predictor algorithm and is called the SMITHPI controller.This study also demonstrates the stability of the controller and its robustness against network parameter variations such as the number of TCP connections,time delays,and user datagram protocol flows.The performance,robustness,and effectiveness of the proposed SMITHPI controller are evaluated using the NS-2 simulator.Finally,the performance of the SMITHPI controller is compared with that of a well-known queue-based AQM,called the proportional-integral controller.
