Internet中的包延迟分布与包丢失关系研究

包延迟的分布特征是Internet端到端行为特征的一个重要组成部分,前人已在该方面进行了大量研究,但许多研究结论只适用于丢包率较小的情况,通过研究我国科技网和教育网上34条端到端路径上的延迟特征,得出了如下结论：（1）包延迟的分布特征与丢包率存在一定的关系;（2）在丢包率较小的情况下,包延迟的分布多具有单峰性,但随着丢包率的增大,包延迟的分布不再具有单峰性,而是呈现出越来越分散的特点;（3）随着丢包率的增大,固有延迟的发生次数呈现逐渐减少的趋势,当丢包率增大到一定程度,固有延迟的发生次数就很少了。     

基于RTW的空间机器人遥操作实时仿真系统

搭建了一套实时仿真系统以作为空间机器人遥操作的研究平台.系统以两台PC机分别模拟主从端的运行情况,主端PC连接通用力反馈游戏手柄作为主手输入设备,从端PC挂接嵌入式处理器(PC/104)用作空间机械手的实时仿真;主从端信号传输时延根据TCP/IP协议由软件模拟产生.利用Madab中的RTW/xPC Target工具箱将空间机械手模型编译为实时可执行代码,下载到嵌入式处理器(PC/104)实时执行,保证了手柄输入和空间机械手Simulink模型间的时钟同步.结合给定模型数据,完成了空问机械手实时位置跟踪实验,证明了系统搭建方案的可行性.系统对空间机器人遥操作的研究起到了很好的支撑作用.     

基于共享缓存的无线网络呼叫接纳控制算法

针对移动网络中新的增值数据业务的增加、性能指标多样化的现状,提出了一种具有共享缓存、支持可变比特率业务的接入网系统模型,给出了性能参数的计算方法、兼顾分组层性能参数(丢包率和平均时延)和连接层性能参数的CAC算法,数值计算结果表明了该方法的正确性。     

A comparison between optimization algorithms applied to synchronization of bilateral teleoperation systems against time delay and modeling uncertainties

The goal of this paper is to achieve optimal performance for synchronization of bilateral teleoperation systems against time delay and modeling uncertainties, in both free and contact motions. Time delay in bilateral teleoperation systems imposes a delicate tradeoff between the conflicting requirements of stability and transparency. To this reason, in this paper, population-based optimization algorithms are employed to tuning the proposed controller parameters. The performance of tuned controllers is compared with the gains obtained by Cuckoo Optimization Algorithm (COA), Biogeography-Based Optimization (BBO), Imperialist Competitive Algorithm (ICA), Artificial Bee Colony (ABC), Particle Swarm Optimization (PSO), Genetic Algorithm (GA), Ant Colony Optimization with continuous domain (ACOR), Self-adaptive Differential Evolution with Neighborhood Search (SaNSDE), Adaptive Differential Evolution with Optional External Archive (JADE), Differential Evolution with Ensemble of Parameters and mutation strategies (EPSDE) and Cuckoo Search (CS). Through numerical simulations, the validity of the proposed method is illustrated. It is also shown that the COA algorithm is able to solve synchronization problem with high performance in stable transparent bilateral teleoperation systems.     

一种用于分组无线网的TDMA方案

在无线分组网中,基于竞争机制的信道多址方法常由于分组冲突而限制网络性能,不能满足战术信息传输的实时可靠性要求。该文提出了采用TDMA机制构建无中心网络的应用方案,按时隙分配信道资源,避免分组竞争,保证各节点数据信息在其专有时隙及时、可靠地发送,并通过预留时隙适应节点变化和突发通信的需求。采用GPS同步及DSP通信协议板完成了系统的具体实现,能更好地适应战术无线分组网的传输特点和应用需求。     

一种节能的无线传感器网络报文优化算法

针对传感嚣数据传输过程中报文的有效数据比例较低所造成的能量浪费问题,提出一种基于无线信道误码率的报文优化算法（BGPP）,该算法根据接收者反馈的无线信道的误码率动态调整发送报文的长度,采用无损的数据聚集方法来提高报文中的有效数据比例．实验结果表明,BGPP算法可以适应无线信逆状态的动态变化,在无线信逆误码率较低的情况下具有较好的节能效果。     

Stability analysis of a rigid robot with output-based controller and time delay

This study considers the problem of stabilizing a rigid robot with an output-based controller and time-delayed input functions applied to the robot joints. We establish sufficient conditions for asymptotic stability of the system under consideration. These conditions are based on well-defined relationships between the magnitude of the controller gains and the time delay factor.     

Passive position error correction in Internet-based teleoperation

During the last two decades, important advances have been made in the field of bilateral teleoperation. Different techniques for performing stable teleoperation in non-ideal conditions have been developed, especially in a passivity framework. Until recently, however, no robust solutions for addressing this problem with variable delays and other drawbacks of packet-switched networks have been developed. The requirement of maintaining passivity in these circumstances degrades performance, due to the loss of energy that it involves. In this paper an arrangement is proposed which is capable of eliminating position errors, while maintaining passivity of an Internet-like channel. The behaviour of this new controller is studied by Lyapunov analysis, compared to previous methods, and validated through numerical simulations.     

An optimal control method for applications using wireless sensor/actuator networks

The wireless sensor/actuator networks (WSANs) can be used for spatially distributed control systems. With smart sensors and actuators, the WSANs are able to not only sense the control system states and report measurements, but also perform control and actuation. This paper investigates WSANs on their ability of control. A centralized controller is introduced into WSANs to make up closed-loop control systems, in which control decisions are made based on global network-wide information. A model of the control and communication over WSANs is made theoretically, based on which we achieved an optimal control method. It is demonstrated by simulations that the control method proposed could stabilize the control system quickly.     

机器人控制器中应用加速度反馈的几个问题讨论

加速度正反馈与近似积分负反馈相结合的综合加速度反馈在机械手位置控制中的应用有明显的增阻尼效果,而在力控制中的应用却受到了很多条件的限制.利用PUMA560机械手力控制的辨识模型,通过仿真手段分析了影响加速度反馈效果的原因,得出了机械手驱动电机的动态、连杆的柔性和采样延迟是制约加速度反馈作用的主要因素的结论.最后在此结论指导下的实验结果验证了这个结论的正确性,同时指出了应用加速度反馈的希望所在.     

VOIP动态缓出时延算法研究分析

在以包为单位进行数据传输合、语音应用程序(VOIP,Voice Over Internet Protocol)中,为了补偿数据包在网络传输中不可预知的网络传输延迟,在接收端首先必须把接收到的数据包缓存起来,缓存一定的时间再播放出来,以减少通话的抖动,得到比较满意的通话质量。文章主要研究动态缓出时延算法,力求使这个缓出时延尽可能小,同时尽可能减少包的丢失率。文章提出了一个有效动态缓出时延算法,该算法主要跟踪最近到达的数据包的网络传输时延求出其近似分布函数,并利用这些信息和延迟峰的侦测算法预测下一个语音峰的缓出时延。实验结果表明利用该算法可以在缓出时延和包丢失率之间达到最佳平衡,是一种理想、有效的算法。     

Compensation for control packet dropout in networked control systems

With the integration of communication networks and distributed control in modern manufacturing and process industries, networked control systems (NCSs) are becoming increasingly important due to its simplicity, scalability, flexibility, and cost effectiveness. However, there are still significant technical barriers that limit the applications of NCS technologies. Two challenges are network-induced time delay and data packet dropout. Applying a real-time queuing protocol that we developed recently, we are able to limit the sum of the network-induced communication delay and the control computation delay within a control period. This one-period delay is further guaranteed by well designed compensation for control packet dropout. Then, this paper proposes to compensate for the control packet dropout at the actuator using past control signals. Three model-free strategies for control packet dropout compensation, namely, PD (proportional plus derivative), PD2 (proportional plus up to the second-order derivative), and PD3 (proportional plus up to the third-order derivative) are developed. They are suitable for a large number of NCSs without the need to tune the compensator parameters. The proposed dropout compensation schemes are demonstrated through numerical examples.     

WSNs中基于占空比间隔优化的延迟约束路由算法

针对WSNs中现有路由算法存在的各种不足,本文提出了一种基于占空比间隔优化的延迟约束路由算法。具体来说,在提出的算法中,首先,将端到端延迟分布估计为占空比间隔和潜在转发器数量的函数,在给定的网络模型和参数下,其分布可以近似地估计。然后,选择满足延迟约束成功率(Delay-Constrained Success Ratio,DCSR)要求的占空比间隔最大值,每个节点独立地调度其休眠和唤醒时间,发送端节点将数据包转发给潜在转发器中最先唤醒的节点,从而确保数据包以要求的概率即DCSR到达接收器,同时最大化占空比间隔;仿真实验结果表明,提出的路由算法不仅能够满足要求的DSCR,并在ETE延迟、数据包交付率和实际得到的DCSR方面都优于现有的先进算法。     

PTP网络非对称时延抖动修正算法设计与分析

为了改进PTPV2时间同步网络非对称时延抖动对主从时钟同步精度的影响,设计了传输报文的非对称时延抖动修正算法。基本思路是在主从时钟交换报文信息中,找出最佳报文用于从时钟的调整。采用两级过滤先进增强时间恢复算法,即使发生网络传输阻塞,也能筛选出未受阻塞的幸运报文用于时钟偏差估计。新算法能够很容易集成到PTPV2协议中,而不会影响基本的报文信息交换。实际测试结果表明,新设计的时间恢复算法,在普通交换机网络中,可有效抑制非对称时延抖动,主从时钟同步精度也可优于100ns。     

无线传感器网络延迟层次型时间同步算法

时间同步在无线传感器网络的许多应用和协议中都有重要的作用,提高同步精度和降低能量消耗是无线传感器网络时间同步算法考虑的两个重要指标.为了改善中小型网络的时间同步性能,针对成簇的网络结构,提出一种基于分簇的延迟层次型时间同步算法(DHTS),建立系统模型并应用DHTS算法,分析了模型拓扑结构和算法同步误差.模拟结果表明,与传统算法相比,DHTS使所有的节点都得到了有效同步,能够在保证网络同步精度的前提下有效降低数据传输所需能量,并且能方便地应用于现实的无线传感器网络.     

低开销的无线传感器网络时间同步算法研究

传统的TPSN时间同步算法虽然能快速而高效地同步网络上节点的时间,但是在节点频繁加入和失效的情况下,其效率低下。针对以上不足,提出了一种改进的无线传感器网络时间同步算法———ITPSN。该算法不需要构建网络的拓扑结构,能高效地处理网络中节点加入和节点失效情况下的时间同步。实验结果表明,该算法明显提高了网络的健壮性,在节点密集部署的情况下,减少了节点的能量消耗,从而提高了节点的使用寿命。