In order to analyze the failure data from repairable systems, the homogeneous Poisson process (HPP) is usually used. In general, HPP cannot be applied to analyze the entire life cycle of a complex, re-pairable system ...In order to analyze the failure data from repairable systems, the homogeneous Poisson process (HPP) is usually used. In general, HPP cannot be applied to analyze the entire life cycle of a complex, re-pairable system because the rate of occurrence of failures (ROCOF) of the system changes over time rather than remains stable. However, from a practical point of view, it is always preferred to apply the simplest method to address problems and to obtain useful practical results. Therefore, we attempted to use the HPP model to analyze the failure data from real repairable systems. A graphic method and the Laplace test were also used in the analysis. Results of numerical applications show that the HPP model may be a useful tool for the entire life cycle of repairable systems.展开更多
Several software reliability growth models （SRGM） have been developed to monitor the reliability growth during the testing phase of software development. In most of the existing research available in the literatures...Several software reliability growth models （SRGM） have been developed to monitor the reliability growth during the testing phase of software development. In most of the existing research available in the literatures, it is considered that a similar testing effort is required on each debugging effort. However, in practice, different types of faults may require different amounts of testing efforts for their detection and removal. Consequently, faults are classified into three categories on the basis of severity： simple, hard and complex. This categorization may be extended to r type of faults on the basis of severity. Although some existing research in the literatures has incorporated this concept that fault removal rate （FRR） is different for different types of faults, they assume that the FRR remains constant during the overall testing period. On the contrary, it has been observed that as testing progresses, FRR changes due to changing testing strategy, skill, environment and personnel resources. In this paper, a general discrete SRGM is proposed for errors of different severity in software systems using the change-point concept. Then, the models are formulated for two particular environments. The models were validated on two real-life data sets. The results show better fit and wider applicability of the proposed models as to different types of failure datasets.展开更多
在用户数量激增的应急通信场景下,为保证地面用户的通信质量,提出了基于距离约束的用户自适应接入方案。首先采用泊松点距离约束策略(Poisson Point under Distance Constraint,PPDC)对无人机(Unmanned Aerial Vehicle,UAV)的位置进行建...在用户数量激增的应急通信场景下,为保证地面用户的通信质量,提出了基于距离约束的用户自适应接入方案。首先采用泊松点距离约束策略(Poisson Point under Distance Constraint,PPDC)对无人机(Unmanned Aerial Vehicle,UAV)的位置进行建模,避免无人机区域重叠带来的干扰问题。其次,引入基站负载传输协议(Base Station Load Transfer Protocol,BSLTP),当接入基站的用户数量超过给定阈值时,超载用户由无人机提供服务。此外,分别分析了地面基站和无人机的覆盖性能,得到了系统整体覆盖概率,并研究了无人机高度、覆盖半径、激增用户密度对网络覆盖性能的影响。最后,通过仿真验证了理论结果的正确性,且所提部署方案能够有效提升网络覆盖性能。展开更多
无人机(unmanned aerial vehicles,UAV)在空间内不规则分布和移动给系统设计带来巨大挑战,为了对UAV服务下的热点场景进行更加真实可靠地分析,基于随机几何和移动ad hoc网络(mobile ad hoc network,MANET)理论,构建了一种三维移动UAV网...无人机(unmanned aerial vehicles,UAV)在空间内不规则分布和移动给系统设计带来巨大挑战,为了对UAV服务下的热点场景进行更加真实可靠地分析,基于随机几何和移动ad hoc网络(mobile ad hoc network,MANET)理论,构建了一种三维移动UAV网络模型。UAV群被建模为三维泊松点过程(three-dimensional Poisson point process,3-D PPP),可以在水平和竖直方向位移。为了进一步研究该系统的网络性能,考虑了2种服务模型:基站切换模型(base station handover model,BHM)和基站恒定模型(base station constant model,BCM)。通过推导服务距离分布以及其余基站干扰的拉普拉斯变换,得出该系统的覆盖概率和信道容量。通过仿真分析了不同参数指标对覆盖概率以及信道容量的影响。实验结果表明,与传统二维UAV网络模型相比,该三维动态模型能够更准确地反映实际情况,并且基于最近邻策略的基站切换能够显著提升网络性能。展开更多
Cloud radio access networks （C-RANs） were proposed as promising solutions to increase both spectrum and energy efficiency performance in next generation wireless communication systems. Much works discussed the concr...Cloud radio access networks （C-RANs） were proposed as promising solutions to increase both spectrum and energy efficiency performance in next generation wireless communication systems. Much works discussed the concrete implementation technology to justify the huge development potential of C-RAN. However, only a few litterateurs focused on characterizing the physical layer security in the downlink. The authors studied the physical layer security in downlink heterogeneous C-RAN systems in the article. To characterize the random deployment of remote radio units （RRUs） with single antenna configuration, the stochastic geometry is based to evaluate the proposals＇ secrecy transmission capacity performances, where the closed-form expressions are derived. Furthermore, two security strategies based on eavesdropper neutralization region to protect the target RRU user against eavesdropping were presented and analyzed. Simulation illustrates the secrecy transmission capacity performance limits on different system parameters. The presented security strategies show a significant enhancement on the secrecy performance.展开更多
Due to irregular deployment of small base stations （SBSs）, the interference in cognitive heterogeneous networks （CHNs） becomes even more complex; in particular, the uncertainty of spectrum mobility aggravates the ...Due to irregular deployment of small base stations （SBSs）, the interference in cognitive heterogeneous networks （CHNs） becomes even more complex; in particular, the uncertainty of spectrum mobility aggravates the interference context. In this case, how to analyze system capacity to obtain a closed-form expression becomes a crucial problem. In this paper we employ stochastic methods to formulate the capacity of CHNs and achieve a closed-form expression. By using discrete-time Markov chains （DTMCs）, the spectrum mobility with respect to the arrival and departure of macro base station （MBS） users is modeled. Then an integral method is proposed to derive the interference based on stochastic geometry （SG）. Also, the effect of sensing accuracy on network capacity is discussed by concerning false-alarm and miss-detection events. Simulation results are illustrated to show that the proposed capacity analysis method for CHNs can approximate the conventional sum methods without rigorous requirement for channel station information （CSI）. Therefore, it turns out to be a feasible and efficient way to capture the network capacity in CHNs.展开更多
文摘In order to analyze the failure data from repairable systems, the homogeneous Poisson process (HPP) is usually used. In general, HPP cannot be applied to analyze the entire life cycle of a complex, re-pairable system because the rate of occurrence of failures (ROCOF) of the system changes over time rather than remains stable. However, from a practical point of view, it is always preferred to apply the simplest method to address problems and to obtain useful practical results. Therefore, we attempted to use the HPP model to analyze the failure data from real repairable systems. A graphic method and the Laplace test were also used in the analysis. Results of numerical applications show that the HPP model may be a useful tool for the entire life cycle of repairable systems.
文摘Several software reliability growth models （SRGM） have been developed to monitor the reliability growth during the testing phase of software development. In most of the existing research available in the literatures, it is considered that a similar testing effort is required on each debugging effort. However, in practice, different types of faults may require different amounts of testing efforts for their detection and removal. Consequently, faults are classified into three categories on the basis of severity： simple, hard and complex. This categorization may be extended to r type of faults on the basis of severity. Although some existing research in the literatures has incorporated this concept that fault removal rate （FRR） is different for different types of faults, they assume that the FRR remains constant during the overall testing period. On the contrary, it has been observed that as testing progresses, FRR changes due to changing testing strategy, skill, environment and personnel resources. In this paper, a general discrete SRGM is proposed for errors of different severity in software systems using the change-point concept. Then, the models are formulated for two particular environments. The models were validated on two real-life data sets. The results show better fit and wider applicability of the proposed models as to different types of failure datasets.
文摘在用户数量激增的应急通信场景下,为保证地面用户的通信质量,提出了基于距离约束的用户自适应接入方案。首先采用泊松点距离约束策略(Poisson Point under Distance Constraint,PPDC)对无人机(Unmanned Aerial Vehicle,UAV)的位置进行建模,避免无人机区域重叠带来的干扰问题。其次,引入基站负载传输协议(Base Station Load Transfer Protocol,BSLTP),当接入基站的用户数量超过给定阈值时,超载用户由无人机提供服务。此外,分别分析了地面基站和无人机的覆盖性能,得到了系统整体覆盖概率,并研究了无人机高度、覆盖半径、激增用户密度对网络覆盖性能的影响。最后,通过仿真验证了理论结果的正确性,且所提部署方案能够有效提升网络覆盖性能。
文摘无人机(unmanned aerial vehicles,UAV)在空间内不规则分布和移动给系统设计带来巨大挑战,为了对UAV服务下的热点场景进行更加真实可靠地分析,基于随机几何和移动ad hoc网络(mobile ad hoc network,MANET)理论,构建了一种三维移动UAV网络模型。UAV群被建模为三维泊松点过程(three-dimensional Poisson point process,3-D PPP),可以在水平和竖直方向位移。为了进一步研究该系统的网络性能,考虑了2种服务模型:基站切换模型(base station handover model,BHM)和基站恒定模型(base station constant model,BCM)。通过推导服务距离分布以及其余基站干扰的拉普拉斯变换,得出该系统的覆盖概率和信道容量。通过仿真分析了不同参数指标对覆盖概率以及信道容量的影响。实验结果表明,与传统二维UAV网络模型相比,该三维动态模型能够更准确地反映实际情况,并且基于最近邻策略的基站切换能够显著提升网络性能。
基金supported by the National Natural Science Foundation of China (U1035001)
文摘Cloud radio access networks （C-RANs） were proposed as promising solutions to increase both spectrum and energy efficiency performance in next generation wireless communication systems. Much works discussed the concrete implementation technology to justify the huge development potential of C-RAN. However, only a few litterateurs focused on characterizing the physical layer security in the downlink. The authors studied the physical layer security in downlink heterogeneous C-RAN systems in the article. To characterize the random deployment of remote radio units （RRUs） with single antenna configuration, the stochastic geometry is based to evaluate the proposals＇ secrecy transmission capacity performances, where the closed-form expressions are derived. Furthermore, two security strategies based on eavesdropper neutralization region to protect the target RRU user against eavesdropping were presented and analyzed. Simulation illustrates the secrecy transmission capacity performance limits on different system parameters. The presented security strategies show a significant enhancement on the secrecy performance.
基金Project supported by the National Basic Research Program （973） of China （No. 2012CB315801）, the National Natural Science Foundation of China （Nos. 61302089 and 61302081）, and the State Major Science and Technology Special Projects （No. 2013ZX03001025-002）
文摘Due to irregular deployment of small base stations （SBSs）, the interference in cognitive heterogeneous networks （CHNs） becomes even more complex; in particular, the uncertainty of spectrum mobility aggravates the interference context. In this case, how to analyze system capacity to obtain a closed-form expression becomes a crucial problem. In this paper we employ stochastic methods to formulate the capacity of CHNs and achieve a closed-form expression. By using discrete-time Markov chains （DTMCs）, the spectrum mobility with respect to the arrival and departure of macro base station （MBS） users is modeled. Then an integral method is proposed to derive the interference based on stochastic geometry （SG）. Also, the effect of sensing accuracy on network capacity is discussed by concerning false-alarm and miss-detection events. Simulation results are illustrated to show that the proposed capacity analysis method for CHNs can approximate the conventional sum methods without rigorous requirement for channel station information （CSI）. Therefore, it turns out to be a feasible and efficient way to capture the network capacity in CHNs.
