Global Navigation Satellite System(GNSS)-based continuous and accurate train positioning is one of the key technologies for advanced train operations such as train virtual coupling.However,GNSS-based train positioning...Global Navigation Satellite System(GNSS)-based continuous and accurate train positioning is one of the key technologies for advanced train operations such as train virtual coupling.However,GNSS-based train positioning faces significant challenges in real-world scenarios due to environmental complexities and signal interferences.Considering this issue,this paper presents an approach for modeling and performance analysis of GNSS-based train positioning systems using Colored Petri Nets(CPNs).By systematically modeling the GNSS signal reception and processing process,the performance of the positioning system under various environment scenarios is evaluated.The system model integrates three types of interference signals(i.e.,Amplitude Modulation(AM)signals,Frequency Modulation(FM)signals,and pulse signals)while incorporating environmental factors such as terrain obstructions and tunnel shielding.Additionally,the Extended Kalman Filter(EKF)algorithm is employed to process GNSS observation data,providing accurate train position estimations.The simulation results demonstrate that signal interferences and complex environmental conditions significantly affect the GNSS-based positioning accuracy.This study offers a comprehensive framework for evaluating the performance of GNSS-based train positioning systems in different scenarios,highlighting critical factors that influence positioning accuracy and stability.展开更多
The integrated modular avionics （IMA） architecture is an open standard in avionics industry, in which the number of functionalities implemented by software is greater than ever before. In the IMA architecture, the r...The integrated modular avionics （IMA） architecture is an open standard in avionics industry, in which the number of functionalities implemented by software is greater than ever before. In the IMA architecture, the reliability of the avionics system is highly affected by the software applications. In order to enhance the fault tolerance feature with regard to software application failures, many industrial standards propose a layered health monitoring/fault management （HM/FM） scheme to periodically check the health status of software application processes and recover the malfunctioning software process whenever an error is located. In this paper, we make an analytical study of the HM/FM system for avionics application software. We use the stochastic Petri nets （SPN） to build a formal model of each component and present a method to combine the components together to form a complete system model with respect to three interlayer query strategies. We further investigate the effectiveness of these strategies in an illustrative system.展开更多
Weighted priority queueing is a modification of priority queueing that eliminates the possibility of blocking lower priority traffic. The weights assigned to priority classes determine the fractions of the bandwith th...Weighted priority queueing is a modification of priority queueing that eliminates the possibility of blocking lower priority traffic. The weights assigned to priority classes determine the fractions of the bandwith that are guaranteed for individual traffic classes, similarly as in weighted fair queueing. The paper describes a timed Petri net model of weighted priority queueing and uses discrete-event simulation of this model to obtain performance characteristics of simple queueing systems. The model is also used to analyze the effects of finite queue capacity on the performance of queueing systems.展开更多
To achieve high quality of service （QoS） on computational grids, the QoS-aware job scheduling is investigated for a hierarchical decentralized grid architecture that consists of multilevel schedulers. An integrated ...To achieve high quality of service （QoS） on computational grids, the QoS-aware job scheduling is investigated for a hierarchical decentralized grid architecture that consists of multilevel schedulers. An integrated QoS-aware job dispatching policy is proposed, which correlates priorities of incoming jobs used for job selecting at the local scheduler of the grid node with the job dispatching policies at the global scheduler for computational grids. The stochastic high-level Petri net （SHLPN） model of a two-level hierarchy computational grid architecture is presented, and a model refinement is made to reduce the complexity of the model solution. A performance analysis technique based on the SHLPN is proposed to investigate the QoS-aware job scheduling policy. Numerical results show that the QoS-aware job dispatching policy outperforms the QoS-unaware job dispatching policy in balancing the high-priority jobs, and thus enables priority-based QoS.展开更多
The short-range wireless communication technology has advanced considerably and provides the feasibility of train-train(T2T)communication link in the communication-based train control system.The introduction of the T2...The short-range wireless communication technology has advanced considerably and provides the feasibility of train-train(T2T)communication link in the communication-based train control system.The introduction of the T2T link would reduce the headway and improve operational efficiency.Formal methods are system design techniques that use rigorously specified mathematical models to ensure all behaviors work as expected.And it is exactly the functional safety verification needed.Therefore,to deal with the functional safety verification of the T2T link,an untimed colored petri net model is first constructed.Secondly,the verification process is performed.Conclusions can be drawn from the state space report and the computation tree logic queries.Lastly,the model is parameterized,and then data log files are obtained for further performance measurement.Results show that the proposed criteria are satisfied and there are no defects in the basic design requirements.The transmission delay has considered the reconnection,transmission errors and the interruption.The probability of the delay lower than 150 ms accounts for 98.106%,which meets the specification and the previous field test.展开更多
With the rapid development of various applications of Information Technology,big data are increasingly generated by social network services(SNS)nowadays.The designers and providers of SNS distribute different client a...With the rapid development of various applications of Information Technology,big data are increasingly generated by social network services(SNS)nowadays.The designers and providers of SNS distribute different client applications for PC,Mobile phone,IPTV etc.,so that users can obtain related service via mobile or traditional Internet.Good scalability and considerably short time delay are important indices for evaluating social network systems.As a result,investigating and mining the principle of users’behaviors is an important issue which can guide service providers to establish optimal systems with SNS.On the basis of analyzing the characteristics of social network system,this paper constructed a Stochastic Petri Net(SPN)model for describing the behaviors of three users for SNS.Moreover,the scalability of users’behaviors of SNS was studied by extending the SPN model of three users to the one of four users.Furthermore,average time delay was chosen as the performance index to evaluate the performance of these two constructed SPN models with Stochastic Petri Net Package(SPNP)6.0.For different parameters of number of connections,traffic load and buffer size,various trends and numerical results are derived thereby.The methodology of modeling and simulation in this paper can be further used to study the performance of SNS.展开更多
针对航班地面保障实际作业流程的精准刻画与性能评估,提出一种多层级航班地面保障随机Petri网(Stochastic Petri Net,SPN)构建及性能分析方法.将保障节点间的衔接过程与保障节点进行过程同时作为随机Petri网的变迁,构建多层级航班地面保...针对航班地面保障实际作业流程的精准刻画与性能评估,提出一种多层级航班地面保障随机Petri网(Stochastic Petri Net,SPN)构建及性能分析方法.将保障节点间的衔接过程与保障节点进行过程同时作为随机Petri网的变迁,构建多层级航班地面保障SPN模型解析保障全流程复杂的串并联关系.采用时间性能等价化简方法降低模型分析的难度,在此基础上建立同构马尔科夫链对模型进行性能分析,得到多层级航班地面保障流程SPN模型的库所繁忙率和变迁利用率.建立的输入输出库所繁忙率四象限图可直观揭示流程中的低效与高效运行区域,实现保障节点及衔接过程前后续状态的精准分类,结合变迁利用率结果,并基于变迁平均发生速率动态变化过程中稳态概率累计变化量识别关键保障节点或衔接,包括4个关键保障节点及6个关键节点间的衔接.研究结果表明:航班地面保障的关键部分多集中在前后衔接不紧密的不同节点间,如餐食及机供品配供完成后等待关客舱门衔接过程,即使单个保障节点的作业时间较短,但若其前续准备或后续完成状态耗时较长,易导致整体保障效率降低;当关键保障节点或衔接平均发生速率超过0.2,即对应持续时间缩短至5 min后,保障流程整体持续时间下降趋于稳定.研究成果可以为机场协同决策下目标撤轮挡时间预测准确性的提高及促进机坪运行保障效率提供理论基础和方法支撑.展开更多
基金supported by the National Key Research and Development Program of China(2023YFB3907300)the Fundamental Research Funds for the Central Universities(2024JBMC002)the National Natural Science Foundation of China(T2222015,U2268206).
文摘Global Navigation Satellite System(GNSS)-based continuous and accurate train positioning is one of the key technologies for advanced train operations such as train virtual coupling.However,GNSS-based train positioning faces significant challenges in real-world scenarios due to environmental complexities and signal interferences.Considering this issue,this paper presents an approach for modeling and performance analysis of GNSS-based train positioning systems using Colored Petri Nets(CPNs).By systematically modeling the GNSS signal reception and processing process,the performance of the positioning system under various environment scenarios is evaluated.The system model integrates three types of interference signals(i.e.,Amplitude Modulation(AM)signals,Frequency Modulation(FM)signals,and pulse signals)while incorporating environmental factors such as terrain obstructions and tunnel shielding.Additionally,the Extended Kalman Filter(EKF)algorithm is employed to process GNSS observation data,providing accurate train position estimations.The simulation results demonstrate that signal interferences and complex environmental conditions significantly affect the GNSS-based positioning accuracy.This study offers a comprehensive framework for evaluating the performance of GNSS-based train positioning systems in different scenarios,highlighting critical factors that influence positioning accuracy and stability.
基金supported by the National Grand Fundamental Research Program of China (Nos. 2010CB328105, 2009CB320504)the Tsinghua University Initiative Scientific Research Programthe National Natural Science Foundation of China (Nos. 61070182,60973107, 60973144, 61173008, 61070021)
文摘The integrated modular avionics （IMA） architecture is an open standard in avionics industry, in which the number of functionalities implemented by software is greater than ever before. In the IMA architecture, the reliability of the avionics system is highly affected by the software applications. In order to enhance the fault tolerance feature with regard to software application failures, many industrial standards propose a layered health monitoring/fault management （HM/FM） scheme to periodically check the health status of software application processes and recover the malfunctioning software process whenever an error is located. In this paper, we make an analytical study of the HM/FM system for avionics application software. We use the stochastic Petri nets （SPN） to build a formal model of each component and present a method to combine the components together to form a complete system model with respect to three interlayer query strategies. We further investigate the effectiveness of these strategies in an illustrative system.
文摘Weighted priority queueing is a modification of priority queueing that eliminates the possibility of blocking lower priority traffic. The weights assigned to priority classes determine the fractions of the bandwith that are guaranteed for individual traffic classes, similarly as in weighted fair queueing. The paper describes a timed Petri net model of weighted priority queueing and uses discrete-event simulation of this model to obtain performance characteristics of simple queueing systems. The model is also used to analyze the effects of finite queue capacity on the performance of queueing systems.
基金The National Natural Science Foundation of China(No60673054,90412012)
文摘To achieve high quality of service （QoS） on computational grids, the QoS-aware job scheduling is investigated for a hierarchical decentralized grid architecture that consists of multilevel schedulers. An integrated QoS-aware job dispatching policy is proposed, which correlates priorities of incoming jobs used for job selecting at the local scheduler of the grid node with the job dispatching policies at the global scheduler for computational grids. The stochastic high-level Petri net （SHLPN） model of a two-level hierarchy computational grid architecture is presented, and a model refinement is made to reduce the complexity of the model solution. A performance analysis technique based on the SHLPN is proposed to investigate the QoS-aware job scheduling policy. Numerical results show that the QoS-aware job dispatching policy outperforms the QoS-unaware job dispatching policy in balancing the high-priority jobs, and thus enables priority-based QoS.
基金National Natural Science Foundation of China(No.61963023)。
文摘The short-range wireless communication technology has advanced considerably and provides the feasibility of train-train(T2T)communication link in the communication-based train control system.The introduction of the T2T link would reduce the headway and improve operational efficiency.Formal methods are system design techniques that use rigorously specified mathematical models to ensure all behaviors work as expected.And it is exactly the functional safety verification needed.Therefore,to deal with the functional safety verification of the T2T link,an untimed colored petri net model is first constructed.Secondly,the verification process is performed.Conclusions can be drawn from the state space report and the computation tree logic queries.Lastly,the model is parameterized,and then data log files are obtained for further performance measurement.Results show that the proposed criteria are satisfied and there are no defects in the basic design requirements.The transmission delay has considered the reconnection,transmission errors and the interruption.The probability of the delay lower than 150 ms accounts for 98.106%,which meets the specification and the previous field test.
基金supported by the Excellent Young Teachers Training Project (the second level,Project Number:YXJS201508)Teaching reform projects of Communication University of China (Project Number:JG190033,Project Number:JG22062).
文摘With the rapid development of various applications of Information Technology,big data are increasingly generated by social network services(SNS)nowadays.The designers and providers of SNS distribute different client applications for PC,Mobile phone,IPTV etc.,so that users can obtain related service via mobile or traditional Internet.Good scalability and considerably short time delay are important indices for evaluating social network systems.As a result,investigating and mining the principle of users’behaviors is an important issue which can guide service providers to establish optimal systems with SNS.On the basis of analyzing the characteristics of social network system,this paper constructed a Stochastic Petri Net(SPN)model for describing the behaviors of three users for SNS.Moreover,the scalability of users’behaviors of SNS was studied by extending the SPN model of three users to the one of four users.Furthermore,average time delay was chosen as the performance index to evaluate the performance of these two constructed SPN models with Stochastic Petri Net Package(SPNP)6.0.For different parameters of number of connections,traffic load and buffer size,various trends and numerical results are derived thereby.The methodology of modeling and simulation in this paper can be further used to study the performance of SNS.
文摘针对航班地面保障实际作业流程的精准刻画与性能评估,提出一种多层级航班地面保障随机Petri网(Stochastic Petri Net,SPN)构建及性能分析方法.将保障节点间的衔接过程与保障节点进行过程同时作为随机Petri网的变迁,构建多层级航班地面保障SPN模型解析保障全流程复杂的串并联关系.采用时间性能等价化简方法降低模型分析的难度,在此基础上建立同构马尔科夫链对模型进行性能分析,得到多层级航班地面保障流程SPN模型的库所繁忙率和变迁利用率.建立的输入输出库所繁忙率四象限图可直观揭示流程中的低效与高效运行区域,实现保障节点及衔接过程前后续状态的精准分类,结合变迁利用率结果,并基于变迁平均发生速率动态变化过程中稳态概率累计变化量识别关键保障节点或衔接,包括4个关键保障节点及6个关键节点间的衔接.研究结果表明:航班地面保障的关键部分多集中在前后衔接不紧密的不同节点间,如餐食及机供品配供完成后等待关客舱门衔接过程,即使单个保障节点的作业时间较短,但若其前续准备或后续完成状态耗时较长,易导致整体保障效率降低;当关键保障节点或衔接平均发生速率超过0.2,即对应持续时间缩短至5 min后,保障流程整体持续时间下降趋于稳定.研究成果可以为机场协同决策下目标撤轮挡时间预测准确性的提高及促进机坪运行保障效率提供理论基础和方法支撑.
