Fault Tolerant Control for Networked Control Systems with Packet Loss and Time Delay

In this paper,a fault tolerant control with the consideration of actuator fault for a networked control system （NCS） with packet loss is addressed.The NCS with data packet loss can be described as a switched system model.Packet loss dependent Lyapunov function is used and a fault tolerant controller is proposed respectively for arbitrary packet loss process and Markovian packet loss process.Considering a controlled plant with external energy-bounded disturbance,a robust H ∞ fault tolerant controller is designed for the NCS.These results are also expanded to the NCS with packet loss and networked-induced delay.Numerical examples are given to illustrate the effectiveness of the proposed design method.

Packet-loss-dependent stabilization of NCSs with network-induced delay and packet dropout

This paper is concerned with controller design of net- worked control systems （NCSs） with both network-induced delay and arbitrary packet dropout. By using a packet-loss-dependent Lyapunov function, sufficient conditions for state/output feedback stabilization and corresponding control laws are derived via a switched system approach. Different from the existing results, the proposed stabilizing controllers design is dependent on the packet loss occurring in the last two transmission intervals due to the network-induced delay. The cone complementary lineara- tion （CCL） methodology is used to solve the non-convex feasibility problem by formulating it into an optimization problem subject to linear matrix inequality （LMI） constraints. Numerical examples and simulations are worked out to demonstrate the effectiveness and validity of the proposed techniques.

Kalman Filtering with Partial Markovian Packet Losses

We consider the Kalman filtering problem in a networked environment where there are partial or entire packet losses described by a two state Markovian process. Based on random packet arrivals of the sensor measurements and the Kalman filter updates with partial packet, the statistical properties of estimator error covariance matrix iteration and stability of the estimator are studied. It is shown that to guarantee the stability of the Kalman filter, the communication network is required to provide for each of the sensor measurements an associated throughput, which captures all the rates of the successive sensor measurements losses. We first investigate a general discrete-time linear system with the observation partitioned into two parts and give sufficient conditions of the stable estimator. Furthermore, we extend the results to a more general case where the observation is partitioned into n parts. The results are illustrated with some simple numerical examples.

基于事件触发的Delta算子网络控制系统故障检测

针对网络控制系统在高速采样情况下,网络中由于通信网络带宽受限发生时延和丢包所引起的故障问题,文中采用了基于事件触发机制和Delta算子相结合的故障检测方法。在对故障检测滤波器和控制器进行协同设计的同时,在Delta算子滤波器模型中加入构造向量,避免了参数设计时双线性项的产生。构造δ域的Lyapunov-Krasovskii泛函,对残差系统的稳定性和H∞性能进行分析。数值仿真实例验证了文中所提事件触发机制的有效性,并通过残差评价函数证明了其对故障的灵敏度较高。

基于局部洪泛优化的低轨星座分布式路由算法

针对传统分布式路由算法应用于大型低轨星座时拥塞控制能力有限的问题,提出了基于局部洪泛优化的分布式路由算法。该算法通过局部洪泛的机制收集星间链路的拥塞信息,以应对局部通信需求密集所导致的常见拥塞现象;通过局部路径优化,以较低运行开销实现了流量疏导和网络负载均衡。并且该算法可适用于多层低轨卫星网络结构,不会产生路由环路,对卫星随机故障具有宽适应性。仿真实验表明:该算法在通信需求分布不均的高网络负载情况下能降低2%~10%的丢包率,并对网络随机故障具有鲁棒的表现。

物联网环境下光纤通信网络总线链路丢包率推断

光纤通信网络总线链路在应用过程中容易受到带宽限制,导致光纤通信网络链路丢包率检测精度差、推断效率低,不能满足用户数据传输需求。为此,提出物联网环境下光纤通信网络总线链路丢包率推断方法。根据光纤通信网络路由矩阵,获取物联网环境下光纤网络的通信状态,依据时序分析策略检测网络总线链路数据传输中的薄弱环节,分析不同时段间变量的关联性,建立线性回归模型,计算下个时段预测值,获取总线链路传输状态。计算每条线路的时空关联性,结合背景流量,采用最小二乘法推断链路丢包率。实验结果表明,所提方法的故障识别率高于95%,误差因子与相对误差在0.2和0.02以下,推断耗时低于2 ms,为光纤通信网络的数据传输提供参考。

基于网络控制系统对医院网络安全的分析及优化

近年来,随着医院信息化的迅猛发展,尽管为医院工作带来了便利,但同时带来了网络安全隐.患。网络控制系统(Network Control Systems,NCS)具有成本低、便于创建和维护.灵活性强、便于系统故障诊断等优势,成为一种备受关注的网絡安全隐患消除方案。在利用网絡控制系统維持网絡稳定的过程中,面临时滞、数据丢包、数据包时序错乱等问题,这些实际应用中不可避免的情况使得网絡控制系统的分析和设计变得异常复杂。文章主要研究了网络控制系统的模型建立、稳定性分析以及控制器设计等问题,同时通过进行仿真实验,验证了所得到的理论结果的可行性和有效性。

Design and performance analysis of wireless sensor network location node system for underground mine

Aiming at the application of a wireless sensor network to locating miners in underground mine,we design a wireless sensor network location node system,considering the communication performance and the intrinsic safety. The location node system consists of a mobile node,several fixed nodes,and a sink node,all of whose circuits were designed based on CC2430. A varistor and a RC circuit were used in the reset circuit of a sensor node to guarantee the intrinsic safety by reducing discharge energy,the theoretical analysis of the discharge energy shows that the reset circuit is an intrinsic safety one. The analysis and simulation about the performance of the location node system are discussed,such as network communication delay and packet loss rate,the results show that the highest network communication delay of the system is about 0.11 seconds,and the highest packet loss rate is about 0.13,which assures the location node system has a high reliability,and can locate miners in the underground mine.

Survey on the stability of networked control systems

The insertion of the communication network in the feedback control loop makes the analysis and design of a network control system more complex, and induces some issues that degrade the control system＇s performance and even cause system instability. The main aspects are focused on the stability analysis of Network Control Systems （NCSs） with network-induced delays, data packet dropouts, and multiple-packet transmission. These issues must be considered in the design of an NCS. This work summarizes the main research results, and remarks on some related handling approaches and techniques. The main purpose of the survey is to present the new research state of NCSs and to point out some fields of future work.

A Clustering-tree Topology Control Based on the Energy Forecast for Heterogeneous Wireless Sensor Networks

How to design an energy-efficient algorithm to maximize the network lifetime in complicated scenarios is a critical problem for heterogeneous wireless sensor networks(HWSN).In this paper, a clustering-tree topology control algorithm based on the energy forecast(CTEF) is proposed for saving energy and ensuring network load balancing, while considering the link quality, packet loss rate, etc. In CTEF, the average energy of the network is accurately predicted per round(the lifetime of the network is denoted by rounds) in terms of the difference between the ideal and actual average residual energy using central limit theorem and normal distribution mechanism, simultaneously. On this basis, cluster heads are selected by cost function(including the energy, link quality and packet loss rate) and their distance.The non-cluster heads are determined to join the cluster through the energy, distance and link quality. Furthermore, several noncluster heads in each cluster are chosen as the relay nodes for transmitting data through multi-hop communication to decrease the load of each cluster-head and prolong the lifetime of the network. The simulation results show the efficiency of CTEF. Compared with low-energy adaptive clustering hierarchy(LEACH), energy dissipation forecast and clustering management(EDFCM) and efficient and dynamic clustering scheme(EDCS)protocols, CTEF has longer network lifetime and receives more data packets at base station.

Newapproach to stochastic stability and controller design for networked control systems

This paper addresses the random time-delays and packet losses issues of networked control systems （NCS） within the framework of jump linear systems with mode-dependent time-delays. A new delay-dependent condition on the stochastic stability is proposed by a new stochastic Lyapunov-Krasovskii functional. The condition is formulated as a set of coupled linear matrix inequalities （LMIs）. As an example to verify the proposed method, an inverted-pendulum system with network is considered. The simulation results demonstrate the effectiveness of the method.

Energy Aware Routing Protocol for Cognitive Radio Networks

In this article, a routing protocol EARP (Energy Aware Routing Protocol) with the terminal node is proposed, to deal with the impact of the limited energy resources of Cognitive Radio Networks on the whole network routing. The protocol allows choosing the route from the neighbor nodes in different transmission paths, according to energy consumption of a single node and the full path. If the path breaks, the protocol will increase local routing maintenance strategy. It effectively reduces the retransmission caused by the situation, and improves the routing efficiency. It also can prevent the link transmission process selecting the fault route due to the energy depletion. Through simulation experiments compared with the LEACH (Low Energy Adaptive Clustering Hierarchy) routing protocol, the results showed that in the same experimental environment, the proposed EARP could obviously balance the load, protect low energy nodes, prolong the network survival time and reduce packet loss rate and packet delay of data delivery. So it can improve the energy consumption of sensing node and provide routing capabilities.

Assessment of Quality of Experience (QoE) of Web and Video Services over a Mobile Network Using a Network Emulator

This paper investigates the subjective assessment of QoE of web and video services over a mobile network. To achieve this, the authors used the network emulator (NetEm) traffic control functionality to simulate the dynamic behaviour of a mobile network. Experiments were conducted in a laboratory setting and test conditions were varied to ascertain the QoE, with a focus on QoE metrics such as delay and packet loss ratio. From the experiments conducted, it was observed that there was a negative correlation between delay and average mean opinion score (MOS), and between packet loss ratio and average MOS. The results obtained can be adopted by network operators to provide better services which would lead to improved subscriber base and profitability for the operators and better QoE for the end users.

Reliability and Feedback of Multiple Hop Wireless Networks

This paper analyzes fault-tolerance over the entire design life of a class of multiple-hop wireless networks, where cooperative transmission schemes are used. The networks are subject to both node failure and random channel fading. A node lifetime distribution is modeled with an increasing failure rate, where the node power consumption level enters the parameters of the distribution. A method for assessing both link and network reliabilities projected at the network＇s design life is developed. Link reliability is enhanced through use of redundant nodes. The number of redundant nodes is restricted by the cooperative transmission scheme used. The link reliability is then used to establish a re-transmission control policy that minimizes an expected cost involving power, bandwidth expenditures, and packet loss. The benefit and cost of feedback in network operations are examined. The results of a simulation study under specific node processing times are presented. The study quantifies the effect of loop closure frequency, acknowledgment deadline, and nodes＇ storage capacity on the performance of the network in terms of network lifetime, packet loss rate, and false alarm rate. The study concludes that in a network where energy is severely constrained, feedback must be applied judiciously.

Joint Optimization Strategy for Video Transmission over Distributed Cognitive Radio Networks

A novel joint optimization strategy for the secondary user( SU) was proposed to consider the short-term and long-term video transmissions over distributed cognitive radio networks( DCRNs).Since the long-term video transmission consisted of a series of shortterm transmissions, the optimization problem in the video transmission was a composite optimization process. Firstly,considering some factors like primary user's( PU's) collision limitations,non-synchronization between SU and PU,and SU's limited buffer size, the short-term optimization problem was formulated as a mixed integer non-linear program( MINLP) to minimize the block probability of video packets. Secondly,combining the minimum packet block probability obtained in shortterm optimization and SU's constraint on hardware complexity,the partially observable Markov decision process( POMDP) framework was proposed to learn PU's statistic information over DCRNs.Moreover,based on the proposed framework,joint optimization strategy was designed to obtain the minimum packet loss rate in long-term video transmission. Numerical simulation results were provided to demonstrate validity of our strategies.

Complex Networks: Traffic Dynamics, Network Performance, and Network Structure

This paper explores traffic dynamics and performance of complex networks. Complex networks of various structures are studied. We use node betweenness centrality, network polarization, and average path length to capture the structural characteristics of a network. Network throughput, delay, and packet loss are used as network performance measures. We investigate how internal traffic, through put, delay, and packet loss change as a function of packet generation rate, network structure, queue type, and queuing discipline through simulation. Three network states are classified. Further, our work reveals that the parameters chosen to reflect network structure, including node betweenness centrality, network polarization, and average path length, play important roles in different states of the underlying networks.

A dynamic network Qo S control mechanism based on traffic prediction

A dynamic network Qo S control mechanism was proposed based on traffic prediction. It first predicts network traffic flow and then dynamically distributes network resources, which makes full use of network flow self-similarity and chaos. So it can meet changing network needs very well. The simulation results show that the dynamic Qo S control mechanism based on prediction has better network performance than that based on measurement.

复杂网络中链上数据安全访问控制仿真

数据安全是保证用户访问安全的基础,为了提升控制性能与数据安全性,提出复杂网络环境下链上数据安全访问控制方法。基于复杂网络环境的分析结果提取链路数据特征分量,使用分布式融合方法建立网络链上数据存储的决策树结构模型。以提取的链路数据特征分量为基础,计算网络链上访问数据发送速率、传输往返时间以及丢包率等控制参数,通过丢包率平滑器处理链上数据,结合链上数据平滑处理结果,修正网络访问数据包速率变化参数,完成数据安全访问控制。实验结果表明,使用上述控制方法开展链上数据安全访问控制时,控制性能和安全性能均得到了明显提升。