认知无线网络中基于无休止多臂赌博机模型的多用户频谱接入机制

针对如何协调多个认知用户择机接入多段空闲频域信道的问题,提出了一种基于无休止多臂赌博机(RMAB)模型的动态频谱接入机制。首先,考虑到实际环境下认知用户的信道感知误差,推导出能有效处理感知误差的Whittle索引值算法,该算法通过历史经验积累给予每个信道一定的信任值,并综合考虑在当前信任值下选择每个信道的立即收益与未来收益的多少,选择出需要感知接入的信道;其次,对于多个认知用户接入相同信道时产生冲突的问题,提出了基于多标拍卖的协调机制,通过多标拍卖的方式处理认知用户之间的冲突。仿真结果表明,在相同的环境中,所提出的频谱接入机制与未处理误差的或者未采用多标拍卖的接入机制相比,认知用户获得的吞吐量更大。     

整车电磁仿真模型精度评估

整车模型是车辆电磁性能仿真分析的基本平台,其精度直接决定仿真结果的准确性和可信度。为实现整车电磁仿真模型的量化评估,提出一种整车电磁仿真模型量化精度评估方法。以模型误差反向表征模型精度指标,用整体误差与局部误差的加权求和表征模型总误差,将整体尺寸与曲面面积的加权求和表征整体误差,采用部件偏差的最大值、平均值和变异系数加权求和表征局部误差。根据模型针对的不同分析问题,各加权系数可做适当调整,适用于各种车辆电磁性能分析任务的整车模型精度评价,具有较好的灵活性。仿真结果显示,该方法可准确预估整车模型分析时结果的可信度。     

无线视频流媒体异构接入的二维自适应流控模型研究

TFRC（TCP-Friendly Rate Control）机制适用于视频流媒体UDP流传输的流控,它保证UDP流的吞吐量具备良好的TCP友好特征。异构用户接入也可以借助TFRC机制探测可用带宽,但其在无线信道中面临新的挑战。基于无线信道特征,本文提出一种无线流媒体接入二维自适应流控模型。该模型建立在丢包率（PLR,Packct Loss Ratio）、误码率（BER,Bit Error Ratio）统计的基础上,分别针对包长和帧速率进行二维调节。首先,基于BER统计来调整包长和发送间隔以提供稳定帧速率的流量;其次,根据TFRC方程,由RTT（RoundTripTime）、RTO（Retransmission timeout）、PLR等计算可用带宽,结合帧错误率（FER,Frame Error Ratio）作为帧速率调整指标。仿真结果验证了该模型的有效性。     

基于接入请求时空分布的延迟容忍上传接入控制方法

海洋观测数据的获取是海洋环境保护、防灾减灾、资源开发以及科学研究等的依托与保障.观测节点上传数据的请求的接入调度问题是海洋观测系统的重要研究内容,其根源在于观测节点对稀缺无线通信资源的争用.尽管目前已有大量研究,但是现有技术应用于观测节点快速移动接入上传数据时性能不尽人意.研究解决海量移动观测节点有效的上传接入控制方法迫在眉睫.基于移动接入请求抽象的时空动态模型以及截止时间内被调度的随机性的分析,研究解决保证观测数据延迟容忍且收益最大的移动接入优化调度问题.不幸的是,该问题是NP难的(详见定理1).因此,提出了一种基于动态规划思想的增强接入控制的近似算法(P-RSA)来解决该问题.首先,基于观测接入请求的历史数据分析并构建抽象其动态特征的时空数据模型;其次,基于“流”请求截止时间内经过AP通信覆盖区域的随机性分析,对其“未来收益”进行量化并将其引入优化目标;最后通过模拟实验对截止时间内在不同的AP负载条件下,基于“收益”这个泛化指标对移动接入调度性能进行评估,实验结果验证了该方法的有效性.     

信道接入协议的网络仿真技术研究

应用OPNET仿真平台,针对ALOHA和CSMA/CD,对信道接入协议的建模仿真技术进行了研究。提出了ALOHA与CSMA/CD建模层次框架,实现了对ALOHA与CSMA/CD建模仿真的网络模型、节点模型及进程模型,并通过分析信道吞吐量和利用率参数的仿真结果,对仿真模型的合理性和有效性进行了评估,进而说明了此网络仿真技术的可行性。     

改进的UKF在惯导平台误差模型辨识中的应用

为减小建模误差,建立了基于直接法进行惯导平台误差模型辨识的非线性模型.Unscented Kalman滤波(UKF)是一种新的非线性滤波算法,为此将其引入惯导平台的误差模型辨识中.针对系统模型的特点,对标准UKF算法进行了简化改进.改进的UKF算法计算量小、结构简单,滤波精度与标准UKF一致.同时应用扩展Kalman滤波(EKF)算法和改进的UKF算法进行了惯导平台误差模型辨识仿真研究.仿真结果表明,与EKF算法相比,改进的UKF算法的滤波精度显著提高.     

LTE-A中基于时隙接入的接入拥塞控制优化算法

在LTE-A中，由于物理随机接入信道(Physical Random Access Channel，PRACH)资源有限，当大量的设备几乎同时地向基站发起随机接入请求时，可能会导致接入网拥塞，接入时延增大，无法满足用户的服务质量需求。通过分析时隙接入模型，提出了一种自适应调整时隙接入周期的接入控制优化方案。与基于时隙接入的信道接入控制协议(slotted-access-based channel access control protocol，SCACP)相比，所提方案首先通过实时接入负载的估计，优化时隙接入周期的选择，均衡了接入时隙的接入请求，既保障了设备的接入成功率，又减少了不必要的前导重传，降低了接入时延。最后，仿真结果验证了所提接入控制优化方案的有效性。     

802.16d协议OFDM接入同步误差影响研究

本文首先对802.16协议以及物理层正交频分复用(OFDM)接入方式的协议规范进行了简单介绍。然后在阐述了OFDM的原理和实现技术之后重点针对同步误差的对802.16d物理层OFDM接入方式的影响进行了研究与仿真,并得出结论。     

机器人减速器传动误差建模与优化

为提高工业机器人旋转矢量(RV)减速器的传动精度,合理分配各零件的加工和装配公差,本文提出一种基于等价模型的RV减速器传动误差建模与优化方法.该方法根据RV减速器的传动结构,构建17自由度的等价误差模型,利用传统经验参数进行求解,获得减速器仿真传动误差;同时,将仿真传动误差与实际测量传动误差进行对比,运用最小二乘法建立经验参数辨识模型;在此基础上通过粒子群算法优化辨识模型中的经验参数,将该参数运用到实际RV减速器生产中,结果显示:与传统经验参数建立的误差模型相比,本文提出的方法使得传动精度的仿真精度误差平均缩小9.99%,大幅度提高了等价误差模型的准确性.     

IEEE802.11e无线局域网中的接入延迟分析模型

IEEE802.11e标准为各个服务类别制定了不同的信道竞争参数数值,使得无线局域网具备了业务区分能力。标准中所提出的增强型分布式接入方式主要包括虚拟碰撞、节点回退、最小竞争窗口以及仲裁帧间隔等机制。本文建立三维离散马尔可夫模型分析队列在接入过程中的竞争行为,进而准确估计各个队列的接入延迟。仿真结果表明,该模型能够准确地描述资源竞争情况,接入延迟计算法方法可根据不同系统参数精确地计算接入延迟性能。     

6LoWPAN网络节点信道接入延时性能研究

为了优化6LoWPAN网络MAC协议性能,提出了一种基于饱和负载的时隙CSMA/CA机制的Markov链模型,并对协议主要网络参数进行了数学推导。基于该模型对节点平均接入延时及网络的信道接入概率等参数进行数值计算,重点分析了协议参数对网络延时性能的影响。数学分析表明,该模型较好地描述了基于饱和负载的IEEE 802.15.4 MAC协议的信道竞争接入机制,而合理的协议参数设置能够有效地改善网络节点平均信道接入延时性能。     

Distribution-based bandwidth access scheme in slotted all-optical packet-switched networks

The common approach in an ingress switch to access a slotted all-optical packet-switched network is the TTA (timer-based/threshold-based bandwidth access) bandwidth access scheme in which packet differentiation is provided by a time-out mechanism. In contrast, we propose in this paper the DA (distribution-based bandwidth access) to access the slotted all-optical packet-switched network within a DiffServ domain. Each torrent (the traffic between each pair of ingress and egress switches) is given a bandwidth measured in slots within a frame at an ingress switch. The slots from each torrent are evenly distributed throughout the frame and among the output wavelengths/fibers of the ingress switch. Comparing to the most commonly used technique TTA, we demonstrate that our DA approach can achieve the following: (1) provide each traffic torrent a fairer access to the network bandwidth; (2) reduce the probability of the slot drop rate at the optical network; (3) reduce the excessive bandwidth allocation by the bursty torrents; (4) balance the traffic load much better on wavelength channels; and (5) guarantee a stable edge switch operation to service traffic in which the traffic generation rate to the optical network is lower than the traffic service rate.     

面向对象的工艺信息集成系统GS—CAPP

工艺信息由设计信息和管理信息构成,两者之间的集成在计算机集成制造中起着极其重要的作用。作为工艺信息载体的工艺卡片在形式和内容上表现出多样性。文中运用面向对象的方法,首先构造了一个标准化的工艺卡片模型,使软件系统能支持各类工艺卡片;进而通过动态创建管理规则文件,实现设计、管理信息的有机通信,确保二者之间的无缝集成。据此开发的面向产品的新一代集成化工艺信息系统GS－CAPP,在实际应用中取得了良好的效果。     

Generic Markov model of the contention access period of IEEE 802.15.4 MAC layer

The IEEE-802.15.4 standard is poised to become the global standard for low data rate, low energy consumption Wireless Sensor Networks. By assigning the same sets of contention access parameters for all data frames and nodes, the Contention Access Period (CAP) of the slotted IEEE-802.15.4 currently provides an even channel access functionality and no service differentiation. However, some applications may require service differentiation and traffic prioritization support to accommodate high-priority traffic (e.g., alarms). In order to simulate a scenario in which different sets of access parameters for different node classes can be configured, this paper develops a Markov-chain-based model of the CAP of the IEEE-802.15.4-MAC. Our Markov model can be used to evaluate the impact of mixing node classes in important factors like the throughput, energy consumption, probability of delivery and the packet latency. The model has been used to provide traffic differentiation in a high saturation scenario in which a set of nodes can be configured to increase 76% the probability of sending a packet and reduce 58% latency, with a 69% energy penalty, in comparison with a standard scenario. The accuracy of the Markov model is validated by extensive ns-2 simulations.     

Performance analysis of timer-based burst assembly with slotted scheduling for optical burst switching networks

In this paper, we analyze the performance of a timer-based burst assembly for optical burst switching (OBS) networks. In our analytical model, an ingress edge node has multiple buffers where IP packets are stored depending on their egress edge nodes, and bursts are assembled at the buffers in round-robin manner. Moreover, bursts are transmitted in accordance with slotted scheduling where each burst transmission starts at the slot boundary. We construct a loss model with two independent arrival streams, and explicitly derive the burst loss probability, burst throughput, and data throughput. In numerical examples, we show the effectiveness of our analysis in comparison with the Erlang loss system. It is shown that our model is quite useful for an OBS network with a large number of input and output links.     

基于AADL的混合关键系统随机错误与突发错误安全性分析

许多复杂的嵌入式系统都是混合关键系统(mixed-criticality system,简称MCS).MCS通常需要在指定的关键性(criticality)等级状态下运行,但是它们可能会受到一些危害的影响,这些危害可能会导致随机错误和突发错误,进一步导致执行线程中止,甚至导致系统故障.目前的研究仅集中于对MCS的可调度性分析,未能进一步分析系统安全性,未能考虑线程之间的依赖关系.本文以随机错误和突发错误为研究对象,提出一种集成故障传播分析的基于架构的MCS安全分析方法.使用架构分析和设计语言(Architecture Analysis and Design Language,简称AADL)刻画构件依赖关系.为了弥补AADL的不足,创建新的AADL属性(AADL突发错误属性),并提出新的线程状态机(突发错误行为线程状态机)语义来描述带有突发错误的线程执行过程.为了将概率模型检查应用于安全分析,提出模型转换规则和组装方法,从AADL模型推导出PRISM模型.建立了两个公式,分别获得定量安全属性以验证故障发生的概率,以及定性安全属性以生成相应的正例来求出故障传播路径来进行故障传播分析.最后,以动力艇自动驾驶仪(power boat autopilot,简称PBA)系统为例,验证了该方法的有效性.     

基于云模型的短时交通流预测方法研究

为了提高短时交通流预测的精确性,提出了一种基于云模型的短时交通流智能预测方法.该方法利用云模型拟合交通流,分别用历史交通流和当前交通流建立历史云和当前云,共同生成预测云,用采预测交通流.结合广州市某交叉口交通流量采集数据,进行了仿真试验,以平均绝对误差(MAE)和平均绝对百分比误差(MAPE)两个指标来衡量预测效果,结果表明了该预测方法具有较高的预测精度.该方法既考虑到交通流历史变化,又顾及交通流实时变化,同时将交通流做整体性处理,很好地避开了噪声引起的预测误差问题,兼顾了预测精度和实时性的要求.     

Provision of differentiated performance in Optical Burst Switching networks based on burst assembly processes

Optical Burst Switching (OBS) has been designed as a practical solution for the high-speed transport network using enabling optical technologies, which can work without optical buffering or pure optical signal processing in the intermediate nodes. As a collection of many packets, optical bursts exhibit different traffic characteristics in the bufferless optical core networks compared to the packet-level traffic in the conventional electronic switching systems. However, many OBS studies often neglect this issue by assuming the inputs to be optical bursts when analyzing the system performance. This paper demonstrates that the loss performance of optical bursts is dramatically different when considering burst assembly process at the edge nodes and the connectivity of the core nodes. We develop some analytical models which can model the loss performance more accurately than the traditional methods. Based on our observations, we propose a scheme to support differentiated loss performances for optical bursts by modifying the burst assembly parameters at the source edge nodes. Our scheme is implemented at the edge nodes and there is no specific requirement to the core nodes. Thus, our design provides good flexibility and scalability in the heterogeneous Internet.     

Reconfigurable Optical Bus and Performance Optimization

With the advent of optical fiber and other advanced technologies in solid state,pipelining signals at the wire(or transmission line)level has becomr possible.This has,in turn,made the slotted bus a potential candidate for interconnection networks(IN)for tightly coupled multiprocessor systems.However,a bus an provide only limited bandwidth.Though slotted bus can provide considerably more bandwith in comparison to the traditional non-slotted bus,it is not enough for fine-grain parallel applications run on the shared-memory systems.One well known method to increase the effective bandwidth of a slotted bus in the LAN/MAN environment is to reuse the bandwwidth by reusing slots.However,in a tightly coupled environment reusing slots is not a lucrative option because the significant buffering needs arising from slot reuse will introduce intolerable delay.In this paper we propose a methodology to reuse part of the bandwith available from temporal and spectral bandwidth expansion with none of minimum buffering delay,resulting in significant performance improvement in both the effective throughput and response time(communication latency).The proposed method entails the design and analysis of a re-configurable bus structure with both temporal and spectral bandwidth expansion and a polynomial time algorithm for optimal configurations for given traffic conditionslWe have compared the performance of our reconfigured bus with that of the traditional slotted bus for uniform and localized traffic pattern and founr that the reconfigured bus outperforms the traditional slotted bus substantially in many practical scenarios.     

基于改进eRCNN的局部路网交通流预测

针对误差反馈循环卷积神经网络在运用到短时交通流预测时存在仅仅能接收时序误差序列,忽略交通流误差数据中隐含的空间拓扑特征,且在模型初始化时其采用的通用卷积神经网络初始化方法降低了模型训练效率的问题,本文提出一种优化的误差反馈循环卷积神经网络模型,在误差反馈循环卷积神经网络模型基础上根据预测误差数据的时空特性对误差反馈层进行结构强化,能够处理包含简单空间关系的误差序列。同时通过在模型训练的过程中分离模型产生的历史预测误差和训练误差,使得模型构建过程更加高效,加速了模型收敛速度。通过北京市四环道路交通数据的实验表明,优化的误差反馈循环卷积神经网络预测模型在预测精度、构建效率及鲁棒性上均得到有效提高。