基于Markov切换空间的分布式协同接入控制模型

基于3层架构的映射框架,本文以视频业务为主要研究对象,研究了分布式协同接入控制系统的建模和调控机理。不失一般性,假设视频业务需求近似服从泊松分布,而服务时间服从指数分布,将一个资源节点上的业务接入状态的演化用Markov过程来描述,则所有的N个资源节点的分布式协同接入控制可以由一个Markov切换空间控制过程来阐述。针对构建的Markov切换空间控制系统,基于系统灵敏度的观点对系统性能进行优化,本文提出了基于策略梯度的随机逼近算法;同时,证明了该随机逼近算法的收敛性。此外,本文给出了一个仿真实例来说明此随机逼近算法的有效性。     

A different approach to the analysis of data in life-tests of laser diodes

A different reading of the available I–V curves is proposed for laser diodes whose characteristics display some degradation. In particular, the usual monitoring of the optical power P and of the threshold current I_th is complemented by the inspection of two more parameters, which separately or jointly contribute to the general variation of I_th. These two parameters are related to the simplest laser model, made of an ideal diode that is voltage-clamped under operating conditions, and are completely defined by those same standard measurements that lead to evaluate I_th. A different definition of the failure modes, and a deeper insight in the possible failure mechanisms are derived. Combined voltage and optical power monitoring during constant-current life-tests is also proposed as a more discriminating measurement than usually considered.     

空间目标与环境红外特性理论建模及其场景生成

介绍了空间目标与深空环境红外特性物理建模的基本方法,建立了卫星和深空背景的红外辐射特性理论模型,在此基础上首次从物理现象的角度初步实现了空间目标及其深空环境的动态景象生成。研究结果对空间目标的探测具有一定的参考价值。     

基于马尔科夫过程的半导体激光器空间辐射可靠性分析

通过对半导体激光器辐射效应的分析,得到了器件在空间环境中的损伤规律和退火规律.根据辐射效应的特点,将器件的性能退化表示为泊松过程与指数过程的结合,建立了基于马尔科夫过程的可靠性模型,利用一步概率转移矩阵获得了故障概率分布函数、可靠度函数以及平均故障前时间的计算方式.根据已有数据,对半导体激光器在空间辐射环境中的性能退化过程进行了仿真,得到了总测试时间为100 000 h时器件的故障概率分布曲线,计算得出平均故障前时间约为42 758.9 h,此时器件可靠度为0.451.分析了不同时间条件下器件的状态概率分布律,结果符合器件性能退化的一般规律,能够描述出器件的失效过程.     

Functional specifications and evaluation of commercially available laser diodes for optical space links

Commercially available GaAlAs laser diodes have been tested to predict their behaviour in intersatellite communications. Three types of device with various structures have been investigated: Sharp lasers, Hitachi lasers (single longitudinal mode emission in c.w. operation) and Ortel lasers (multi-longitudinal modes). Two modulation schemes were applied to devices (NRZ and 4-PPM), corresponding to the two possible modulation formats selected for ISL experiments. Each laser had an average power output of 30 mW, whatever the modulation mode. The output signal, emission spectrum and beam divergence were measured. A reduction in peak power was found with some devices. Multimode spectra were detected under 4-PPM modulation.     

空间辐射环境对激光光源阈值电流特性的影响

激光光源是卫星光通信系统中重要的终端部件,其工作性能最终影响和制约着通信系统的稳定性和可靠性。对空间辐射环境下GaAs,InP激光有源材料的阈值电流密度变化进行了深入的理论研究。数值计算结果表明阈值电流密度的变化与辐射粒子注量呈线性关系,InP激光光源较GaAs激光光源具有更优越的空间抗辐射性能。进一步将理想大气条件下辐射对激光光源的影响拓展到真空环境,结果表明真空环境对辐射造成的影响有一定的加剧破坏作用,但是并不明显,真空环境对激光光源的影响作用主要表现为中心波长漂移。     

Finite automaton intrusion tolerance system model based on Markov

To ensure that the system could still provide normal service for legitimate users when the LAN being invaded,a finite automaton intrusion tolerance model was designed.Based on Markov’s theory,the state transformation relationship of the service provided by the system by establishing the state transition probability matrix was described,quantified the transition state and found the key nodes in the system.The maintenance of key nodes could enhance the tolerance of the system and improve the reliability of the service.Experimental comparison shows that this model not only has strong intrusion tolerance,but also has obvious advantages in the integrity of the security system when it is invaded.     

基于层次隐马尔科夫模型和变长语义模式的入侵检测方法

分析了定长系统调用短序列在入侵检测系统应用中的不足,利用进程堆栈中的函数调用返回地址信息,提出了一种变长短序列的语义模式切分方法,并根据这种变长语义模式之间的层次关系和状态转移特性提出了基于层次隐马尔科夫模型的入侵检测方法.实验结果表明,与传统的隐马尔科夫模型相比,基于层次隐马尔科夫模型的入侵检测方法具有更好的检测效果.     

Two-step fabrication of thin film encapsulation using laser assisted chemical vapor deposition and laser assisted plasma enhanced chemical vapor deposition for long-lifetime organic light emitting diodes

A thin film encapsulation layer was fabricated through two-sequential chemical vapor deposition processes for organic light emitting diodes (OLEDs). The fabrication process consists of laser assisted chemical vapor deposition (LACVD) for the first silicon nitride layer and laser assisted plasma enhanced chemical vapor deposition (LAPECVD) for the second silicon nitride layer. While SiN_x thin films fabricated by LAPECVD exhibits remarkable encapsulation characteristics, OLEDs underneath the encapsulation layer risk being damaged during the plasma generation process. In order to prevent damage from the plasma, LACVD was completed prior to the LAPECVD as a buffer layer so that the laser during LACVD did not damage the devices because there was no direct irradiation to the surface. This two-step thin film encapsulation was performed sequentially in one chamber, which reduced the process steps and increased fabrication time. The encapsulation was demonstrated on green phosphorescent OLEDs with I–V-L measurements and a lifetime test. The two-step encapsulation process alleviated the damage on the devices by 19.5% in external quantum efficiency compared to the single layer fabricated by plasma enhanced chemical vapor deposition. The lifetime was increased 3.59 times compared to the device without encapsulation. The composition of the SiNx thin films was analyzed through Fourier-transform infrared spectroscopy (FTIR). While the atomic bond in the layer fabricated by LACVD was too weak to be used in encapsulation, the layer fabricated by the two-step encapsulation did not reveal a Si–O bonding peak but did show a Si–N peak with strong atomic bonding.     

基于扩展传染病模型和马尔可夫链的物联网可用度评估方法

为反映恶意程序传播环境下物联网可用的状态,基于扩展的SEIRD传染病模型和马尔可夫链提出一种物联网可用度评估方法。根据物联网节点的实际状态,扩展经典传染病模型SIR建立SEIRD物联网节点状态转换模型。由物联网节点各个状态之间的动态变化过程,构建物联网节点处于5种状态的概率动力学方程,得到反映各状态转换的马尔可夫矩阵,进一步得到物联网节点的可用度计算方法。以典型的星形和簇形物联网拓扑结构为例,给出整个物联网可用度的评估方法。通过实验,为管理员如何合理部署正常工作节点数、路由数提供建议。研究成果对提高物联网可用度、促进物联网成功应用具有理论指导意义。     

A model for the prediction of EDFA gain in a space radiation environment

Erbium-doped fiber amplifiers (EDFAs) were irradiated with /sup 60/Co /spl gamma/-rays up to a total dose of 3 kGy. Gain measurements and 1310-nm absorption were achieved during the irradiation to characterize the radiation-induced damage on the fiber. A model based on classical equations was developed to perform accurate predictions of the effects of radiation on EDFAs. This model was shown to be consistent with the experiment at various dose rates and temperatures, therefore allowing the extrapolation to a space environment simulation.     

Poly(3-hexylthiophene-2,5-diyl) based diodes for ionizing radiation dosimetry applications

Accurate measurements of radiation dose are essential prerequisites for the safe and effective use of ionizing radiation in diagnostic and therapeutic medical applications. Recently, dosimeters based on organic polymers have been developed for this purpose. In this work, Poly(3-hexylthiophene-2,5-diyl) (P3HT) based organic diodes were evaluated as potential radiation dosimeters by quantifying the radiation-induced photocurrent under various measurement conditions. Control devices were fabricated in which the P3HT was replaced by polystyrene (PS) for the purpose of quantifying the non-photocurrent contribution to the measured signal. Net photocurrent was determined by subtracting the signal from the PS devices from the signal in the P3HT devices under identical measurement conditions. The responses of these devices were tested in various beam qualities: 100 kVp, 180 kVp, 300 kVp and 6 MV, 18 MV photons. The influences of electric field, film thickness and dose rate on dosimeter sensitivity were investigated. The diodes produced a linear increase in current with increasing dose rate. They demonstrated an increase in sensitivity with increased instantaneous dose rate and an increase in sensitivity at the lowest average dose rates studied here. The sensitivities for different energies were 22.9 nC/Gy, 21.8 nC/Gy and 21.4 nC/Gy for 100 kVp, 180 kVp and 300 kVp, respectively; and 14.5 nC/Gy, 14.7 nC/Gy for 6 MV and 18 MV, respectively for device with P3HT thickness 29 μm.     

基于 Markov 模型的分布式队列稳定频谱接入算法

针对认知无线电系统中次级用户队列稳定性问题,通过建立发送状态马尔科夫(Markov)模型,提出了一种基于CSMA的自适应分布式频谱接入算法。次级用户根据感知结果自适应地调整退避时长参数,使稳态服务速率逐渐趋近到达速率,最终达到队列稳定。此外,还在满足对主用户碰撞限制的条件下,推导了次级用户的吞吐量上界,并证明当次级用户的数据到达速率小于此上界时,能够通过所提算法保证队列稳定。仿真结果证明了算法的有效性。     

基于分时MDP的出租车载客预测推荐技术研究

针对出租车盲目寻客导致空载率高的问题,提出了一种出租车载客热点推荐策略,以最大程度优化匹配乘客过程,提高寻客效率.基于出租车历史轨迹数据,结合热点乘客信息的时间序列特性,提出基于循环神经网络的分段预测(SPBR)算法,以及基于分时马尔可夫决策过程(TMDP)的载客推荐模型.实验表明,SPBR算法预测结果的RMSE比SV...     

A nodes scheduling model based on Markov chain prediction for big streaming data analysis

Streaming data analysis is an important part of big data processing. However, streaming data is difficult to be analyzed and processed in real time because of the rapid data arriving speed and huge size of data set in stream model. The paper proposes a nodes scheduling model based on Markov chain prediction for analyzing big streaming data in real time by following three steps: (i) construct data state transition graph using Markov chain to predict the varying trend of big streaming data; (ii) choose appropriate cloud computing nodes to process big streaming data depending on the predicted result of the data state transition graph; and (iii) assign big streaming data to these computing nodes using the load balancing theory, which ensures that all subtasks are accomplished synchronously. Experiments demonstrate that the proposed scheduling algorithm can fast process big streaming data effectively. Copyright © 2014 John Wiley & Sons, Ltd.     

激光陀螺量化过程的概率模型与分析

提出了激光陀螺量化过程的概率分布模型,在此基础上,分析了量化过程对激光陀螺性能的影响,并给出了量化前后陀螺数据均值和方差之间的关系。仿真实验发现,量化前后陀螺数据的均值符合得较好,但方差却没有简单的对应关系,结论对分析激光陀螺的实际性能有着重要的意义。     

An enhanced Markov chain based model for the narrowband LMS channel in built‐up areas

In this paper, a technique to derive the transition probabilities for a Markov chain model for the land mobile satellite (LMS) channel in built‐up areas is presented. This technique contributes to improving empirically derived parameters in that it can account for elevation and street orientation effects as well as building density. Physical‐statistical or ‘virtual city’ techniques are used to relate observed edification statistics to signal attenuation statistics. This methodology can also be applied to generating correlated time‐series for simultaneous links to a constellation of satellites from the same mobile terminal. The proposed approach also allows the generation of enhanced time‐series which take into account diffuse multipath and diffraction effects. Copyright © 2005 John Wiley & Sons, Ltd.     

A software tool for the design of high power PiN diodes based on the numerical study of the reverse characteristics

A physically based model of power PiN diodes was developed to simulate the reverse voltage behavior with purpose of design optimization for specific application. The model includes process simulation and 2D drift-diffusion simulation of the defined geometrical diode structure. The process simulation was adjusted to obtain the same doping profile measured on a known sample. Since bulk silicon and dopants used in high power device production are different from those used in VLSI, various analytical models of impurity diffusion phenomena were considered and parameters calibration was carried out within the range found in the literature to obtain the best fit with measurements. Impact ionization coefficients of the reverse biased diode model were tuned by comparison with measurements on a reference device and exploited to study the dependence of breakdown voltage vs. various technological parameters.A simulation campaign for many different diode structures was conducted.An ad hoc interpolation algorithm was developed and applied for using measurement and simulation results in quick design of diode structures for specific application.     

Markov过程理论在对地攻击靶场效能评估中的应用

利用Markov随机过程理论,建立了攻击机对地攻击作战过程的Markov模型,推导了靶场攻击条件下,目标被击毁概率、目标生存概率、任务成功率、完成任务时间等效能指标的解析表达式.通过实例说明了效能指标的计算过程并进行了相关分析.     

一种基于GRNN模型的5G基站电磁辐射预测方法

为更好地表征5G基站电磁辐射水平,本文针对电磁辐射预测方法进行研究,提出了 一种基于广义回归神经网络(GRNN)模型的基站电磁辐射环境表征方法,对基站周围的理论最大辐射点接地平面处的瞬时宽带电场强度进行预测。在给定天线发射功率、5G基站与其理论最大辐射点的距离和数据传输时间的情况下,利用80%的数据作为训练集,20%的数据作为测试集,所得平均绝对百分比误差(MAPE)为0.087 1,运行时间为3~5 min,表现出较好的预测精确度和较快的运行速度。与其他模型进行对比,预测精确度和求解效率大幅提高,且随着基站周围区域面积增大,优势愈发明显,具有很好的场景适用性。