一种低丢包率无线网络中基于网络编码的广播重传方法

重传是无线网络广播传输中实现错误处理的重要技术.普通重传方法通常逐一发送丢失包来进行错误处理,这种处理在丢包分散的低丢包率无线网络上重传次敷相当大.本文将网络编码减少无线传输信息量的特性应用在低丢包率无线网络广插重传中,提出一种基于网络编码的广播重传方法(BRANC).该方法按照丢失分布概率特点生成新的重传序列;采用基于多节点的网络编码方法进行丢失包组合实现重传.为达到更佳重传目的,进一步分析了编码组合包重传再丢失时的处理.数学分析表明,该方法能保证接收节点的编码可解性.同时重传次数可达到局部最优性;模拟测试结果表明:与普通重传方法相比,BRANC有效地减少了信息包的平均传输次数.提高了传输效率.     

长时延和丢包的网络控制系统保性能控制

为了研究具有长时延和丢包的网络控制系统保性能控制问题,假设传感器由时钟驱动,控制器和执行器由事件驱动,网络时延在两个采样周期之间,丢包具有马尔科夫跳变特性,利用状态增广的方法,把具有长时延和丢包的网络控制系统建模为具有两种运行模式的离散时间马尔可夫跳变系统,把网络时延转化为系统参数矩阵的不确定性.在此基础上,利用马尔可夫线性跳变系统理论和线性矩阵不等式方法,推导出使网络控制系统随机稳定的保性能控制律存在的充分条件,并给出了设计方法.数例仿真说明了所用方法的有效性.     

无线网络环境下移动机器人的控制策略研究

在移动机器人控制性能优化的研究中,针对无线控制网络中存在时延的情况,进行了控制器与补偿器的研究与设计.首先建立了移动机器人动力学模型,并针对模型设计离散反演控制器使移动机器人能够对给定信号进行跟踪.引入无线网络,进而分析网络时延对无线网络控制系统性能的影响,并针对网络时延利用预测控制算法设计控制序列预测补偿器,从而完成在时延存在的情况下仍然可以对移动机器人进行准确控制的无线移动机器人控制系统.仿真结果表明,设计的控制器与补偿器为无线网络环境下移动机器人的控制性能优化提供了参考.     

基于网络模型的综合多速率采样预测控制器

针对网络控制系统(NCS)中存在的网络延迟和数据丢包问题以及网络控制系统的多采样率特性,将预测控制器和网络延迟补偿器相结合,提出一种基于网络模型的综合多速率采样预测控制器.预测控制器利用多步预测、滚动优化、反馈校正控制策略补偿了传感器-控制器传输延迟,网络延迟补偿器补偿了控制器-执行器传输时延和一些未知网络延迟.仿真试验表明,该算法对网络延迟和数据丢包具有一定的补偿作用,提高了网络资源利用率并且保证闭环网络控制系统渐近稳定.     

基于Wi-Fi的无线网络控制系统的仿真研究

近年来,以Wi-Fi为代表的无线局域网（Wireless Local Area Network,WLAN）技术不断发展和成熟,被广泛应用到各个领域。其中,将无线网络与传统控制系统融合起来,形成具备高移动性、可扩展性和灵活性等优势的无线网络控制系统（Wireless Networked Control Systems,WNCS）,成为控制界的研究趋势之一。针对基于Wi-Fi技术的无线网络控制系统进行了研究,利用TrueTime仿真工具箱以及MATLAB/Simulink仿真环境,构建了一个WNCS的仿真系统模型,设计了相应的PID控制器,并研究了网络传输速率、采样周期等网络性能指标对系统控制性能的影响。     

基于Truetime的无线网络温度控制系统研究

无线网络控制系统(WNCS,Wireless Network Control System)具有无需布线、组网和维护方便、易扩展以及良好的移动性等优点,使得无线网络控制系统的分析和设计成为控制界研究的热点之一。针对无线网络控制系统存在的网络时延、丢包、稳定性差的缺陷,着重介绍了一种基于Matlab/Simulink的无线网络系统仿真工具Truetime,通过在Truetime平台下对给定电阻炉温度模型的无线网络进行参数设置、仿真,指导实际无线平台下的温度控制实验,并得到稳定的系统运行。     

基于网络编码的无线网络重传技术

为提高无线网络数据传输效率,减少数据包丢失重传次数,提出一种基于网络编码的丢包重传方法。将网络编码技术应用到无线网络重传过程中,当有数据包丢失时,发送方重传经过网络编码的组合数据包。根据解码规则,网络节点从组合数据包中恢复丢失的数据。理论分析和模拟实验结果表明,该方法能够有效减少重传数据包的次数,提升无线网络编码性能。     

基于RBF神经网络PID控制的无线网络时延控制研究

针对不确定时延影响无线网络控制系统的控制性能、常规PID控制策略无法满足网络控制要求的问题,提出了一种基于RBF神经网络PID控制的无线网络时延控制方案。采用Matlab/Simulink的TrueTime工具箱建立了无线网络时延控制系统仿真模型,介绍了模型中网络模块、执行器模块、控制器模块的设计及RBF神经网络整定PID控制器参数的实现原理。仿真结果表明,与常规PID控制策略相比,RBF神经网络PID控制策略能够在一定程度上降低不确定时延对无线网络控制系统的影响,从而提高无线网络控制系统的稳定性。     

一类具有数据包丢失的网络控制系统的最优控制

针对控制器和执行器均采用时钟驱动且最大丢包率和最大连续丢包长度被限定的短时延网络控制系统,提出一种数据包丢失的估值补偿方法.该方法可以根据历史状态向量和控制向量信息估算出当前的控制量.利用该方法和动态规划算法,导出了离散二次型性能指标下的网络控制系统的最优控制序列,进而给出最优控制律的实现算法.数值仿真算例验证了所得结果的有效性和正确性.     

基于网络QoS的网络化控制系统保性能控制

研究存在时延和丢包的非理想网络传输情况下的网络化控制系统的保性能控制问题,得到了在非理想网络传输情况下的网络化控制系统存在保性能控制律的充分条件,提出了基于网络服务质量(QoS)的网络化控制系统的保性能控制器的设计方法,该方法是一种能够兼顾系统控制性能和网络服务质量的综合性控制方法.通过仿真实例验证了该方法的有效性.     

Resilient control for wireless networked control systems under DoS attack via a hierarchical game

In this paper, the resilient control problem is investigated for a wireless networked control system (WNCS) under denial‐of‐service (DoS) attack via a hierarchical game approach. In the presence of a wireless network, a DoS attacker leads to extra packet dropout in the cyber layer of WNCS by launching interference power. A zero‐sum Markov game is exploited to model the interaction between the transmitter and the DoS attacker under dynamic network environment. Additionally, with the attack‐induced packet loss, an H_∞ minimax controller is designed in the physical layer by using a delta operator approach. Both value iteration and Q‐learning methods are used to solve the hierarchical game problem for the WNCS. The proposed method is applied to a load frequency control system to illustrate the effectiveness.     

Modelling and control of Zigbee-based wireless networked control system with both network-induced delay and packet dropout

A new stochastic switched linear model is established to describe the Zigbee-based wireless networked control system (WNCS) with both network-induced delay and packet dropout. The network-induced delay can be less or longer than one sampling period. A sufficient condition is presented for the exponentially mean square stability of the closed-loop WNCS, and corresponding state feedback controller is designed by using the augmenting technique and multi-Lyapunov approach. Then, combined with carrier sense multiple access with collision avoidance (CSMA-CA) algorithm, a method is given to choose proper parameter values. Finally, a numerical example is provided to demonstrate the effectiveness of the proposed method.     

Optimal controller location in wireless networked control systems

The control performance of wireless networked control systems (WNCS) has been shown to heavily depend on the packet delivery quality of both the sensor‐to‐controller and controller‐to‐actuator communications. Such quality relies on the relative distance between the wireless transmitter and receiver, which naturally raises the challenging problem of controller placement in WNCS for optimal control performance. In this paper, we investigate the optimal controller location (OCL) problem in WNCS based on linear‐quadratic‐Gaussian control strategy. For the one‐hop network case where the controller can only be placed at either the sensor side or the actuator side, we derive a simple yet effective criterion to determine the OCL. For the more general multi‐hop case where the controller can be located at either one of the sensors, relays, or actuators, we obtain the necessary and sufficient condition under which the closed‐loop system is guaranteed to be stable. On the basis of these results, we further transform the OCL problem into an optimization problem that can be solved efficiently. Numerical results are provided to verify our analysis. Copyright © 2013 John Wiley & Sons, Ltd.     

Providing adaptive QoS to layered video over wireless local area networks through real-time retry limit adaptation

Robust streaming of video over 802.11 wireless LANs (WLANs) poses many challenges, including coping with packets losses caused by network buffer overflow or link erasures. In this paper, we propose a novel error protection method that can provide adaptive quality-of-service (QoS) to layered coded video by utilizing priority queueing at the network layer and retry-limit adaptation at the link layer. The design of our method is motivated by the observation that the retry limit settings of the MAC layer can be optimized in such a way that the overall packet losses that are caused by either link erasure or buffer overflow are minimized. We developed a real-time retry limit adaptation algorithm to trace the optimal retry limit for both the single-queue (or single-layer) and multiqueue (or multilayer) cases. The video layers are unequally protected over the wireless link by the MAC with different retry limits. In our proposed transmission framework, these retry limits are dynamically adapted depending on the wireless channel conditions and traffic characteristics. Furthermore, the proposed priority queueing discipline is enhanced with packet filtering and purging functionalities that can significantly save bandwidth by discarding obsolete or un-decodable packets from the buffer. Simulations show that the proposed cross-layer protection mechanism can significantly improve the received video quality.     

利用自适应编码调制的无线网络控制系统的分析和设计

研究了利用自适应编码调制的无线网络控制系统的分析和设计, 自适应编码机制引入无线网络能够提高衰退信道的能量效率, 增加数据传输率. 进一步, 通过等价时延的概念来描述无线传输信道中的时变速率, 干扰和路由特性. 基于时变的网络条件给出了等价时延的上下界. 无线网络控制系统被建模为具有时变输入时延的离散系统. 通过新的时滞系统技术给出了该闭环无线网络控制系统可稳定化的充分条件. 最后, 数值算例表明了所提控制策略的有效性.     

Modeling and control for wireless networked control system

In this paper, the stabilization problem is considered for the class of wireless networked control systems (WNCS). An indicator is introduced in the WNCS model. The packet drop sequences in the indicator are represented as states of a Markov chain. A new discrete Markov switching system model integrating 802.11 protocol and new scheduling approach for wireless networks with control systems are constructed. The variable controller can be obtained easily by solving the linear matrix inequality (LMI) with the use of the Matlab toolbox. Both the known and unknown dropout probabilities are considered. Finally, a simulation is given to show the feasibility of the proposed method.     

Feedback stabilization over wireless network using adaptive coded modulation

In this paper, we apply adaptive coded modulation (ACM) schemes to a wireless networked control system (WNCS)to improve the energy efficiency and increase the data rate over a fading channel. To capture the characteristics of varying rate,interference, and routing in wireless transmission channels, the concepts of equivalent delay (ED) and networked condition index (NCI)are introduced. Also, the analytic lower and upper bounds of EDs are obtained. Furthermore, we model the WNCS as a multicontroller switched system (MSS) under consideration of EDs and loss index in the wireless transmission. Sufficient stability condition of the closed-loop WNCS and corresponding dynamic state feedback controllers are derived in terms of linear matrix inequality (LMI).Numerical results show the validity and advantage of our proposed control strategies.     

基于状态空间模型的无线网络控制仿真研究

针对采用状态空间模型描述的几类无线网络控制系统,介绍了基于TrueTime的无线网络控制系统仿真程序的设计与实现问题。首先介绍了TrueTime工具箱的组成,然后给出了如何利用无线仿真模块实现基于状态空间模型描述的控制系统仿真方法。分别考虑当系统具有单输入多输出、网络诱导时延、数据丢包、时滞脉冲等特性时,利用TrueTime仿真工具箱,如何建立上述系统的无线网络控制仿真模型以及如何编写相应的程序代码。根据上述不同模型的仿真可以看出,对于不同的系统,他们的初始化设置基本相同,而任务代码却有很大的差别。仿真曲线符合理论结果,说明了仿真模型和程序代码的正确性与有效性。     

Resilient control for wireless networked control systems

This paper proposes an approach to quantify the concept of resiliency in terms of Quality of Control (QoC) of a control system. Based on this concept, an intelligent resilient control algorithm (RCA) is presented for wireless networked control systems (WNCS) to maintain operational normalcy in face of wireless interference incidents, such as Radio Frequency (RF) jamming and signal blocking. The proposed algorithm closes the control loop with wireless sensors feasible by significantly increasing control system’s tolerance to data packet loss and delay caused by wireless interference. The proposed algorithm, along with other well developed wireless technologies, has the potential to enable implementing wireless sensors widely in the next generation of industrial automation and control systems.     

水下航行器网络控制系统仿真

传统控制系统的设计方法中忽略了通信网络中的时延和数据包丢失等问题,仅通过传统方法设计的控制器来降低其对控制系统产生的不利影响,严重影响了系统的稳定性;对于水下航行器等对系统性能要求较高的水下控制平台,突破传统使其在网络环境下能够稳定运行显得尤为重要;在此背景下,提出了网络控制系统的设计方案,以水下航行器为控制平台,进行系统建模,设计反馈控制器,使用MATLAB仿真工具TrueTime,研究分析了网络体系结构下时延和丢包对传统控制系统动静态性能的影响;仿真结果表明该设计方法优化了系统性能,为系统在发生网络诱导时延和数据包丢失时能够稳定运行,提供了可靠的参考依据;该设计结果具有普适性,也可以用于导弹、坦克等航行器。