Random Network Delay Research Articles

Adopting Setpoint Weighting Strategy for WirelessHART Networked Control Systems Characterised by Stochastic Delay

In networked control system, such as WirelessHART that is characterized by stochastic delay, the use of proportional integral and differential (PID) controllers is inadequate. This is because PID performs poorly in handling time-delay processes. The main reason for this poor performance is the limitation in the range of stable gain of the controller. Time delay causes oscillatory response of the PID with large gain. Likewise, sluggish response is experienced with small gain of the PID. Also, dead time compensators like smith predictor and internal model controller are difficult to be implemented practically since they require exact model of the process to be controlled. Therefore, this paper proposes the application of setpoint weighting strategy to be used alongside PID controller in a WirelessHART network. This method extends significantly the range of the PID gain, while providing good set point tracking and load regulation. From the simulation and experimental results obtained, the capability of the approach to load regulation and tracking can be seen in its fast recovery from effect of disturbance with minimal overshoot. Thus, a two degree of freedom control is achieved. Results also showed that the method is robust to real-time random variable network delay and model mismatches.

DEALING WITH THE EFFECTS OF RANDOM TIME DELAY AND DATA DROPOUTS IN NETWORKED CONTROL SYSTEMS THROUGH ROBUST CONTROL

The concept of control over network is widely accepted and used in the world of automation, so the stability, safety, and robustness of the distributed and control systems are of key importance for their proper performance. Thus, it is essential to search for solutions of remote control problems like variable time-delay, data-loss, equipment malfunctions, and unauthorized network infiltrations. This paper gives an H ∞ robust control algorithm, which stabilizes a ZigBee networked control system in the presence of random delays, network overload, and data package loss. Key words: networked control systems; robust control; H ∞ -infinity control; data loss; random time delay; ZigBee REFERENCES: [1] R. A. Gupta, M. Y. Chow: Networked Control Systems: Overview and research trends, IEEE Transactions on Industrial Electronics, pp. 2527–2535 (2010). [2] Y. Xia, Y. Gao, L. Yan, et al.: Recent Progress in Networked Control Systems – A Survey, International Journal of Automation and Computing, 12, 4, 343–367 (2015). [3] L. Zhang, H. Gao, O. Kaynak: Network-Induced Constraints in Networked Control Systems – A Survey, IEEE Transactions on Industrial Informatics, 9, 1, 403–416 (2013). [4] Z. Sun, H. Li, J. Wang: Recent advances in networked control systems, International Conference on Control, Automation and Systems, Seoul, Korea, 2007. [5] E. Kamrani, M. Mehraban: Modeling Internet delay dynamics using system identification, Proceedings of ICIT, 2006, pp. 716–721. [6] S. Shakkottai, A. Kumar, A. Karnik, A. Anvekar: TCP performance over end-to-end rate control and stochastic available capacity, IEEE/ACM Transactions on Networking. 2001, pp. 377–391 [7] H. Zhang, J. Yang, C. Su: T-S fuzzy-model-based robust H∞ design for networked control systems with uncertainties, IEEE Transactions on Indian Informatics, 2007, pp. 289–301. [8] Q. Li,, D. Mills: Jitter-based delay-boundary prediction of wide area networks, IEEE/ACM Transactions on Networking, 2001 pp. 578–590,. [9] J. Nilsson, B. Bernhardsson, B. Wittenmark: Stochastic analysis and control of real-time systems with random delays, Automatica, 34, 1, 57–64 (1998). [10] J. Hespanha, P. Haghshtabrizi, Y. Xu: A survey of recent results in networked control systems, Proceedings of IEEE, 2007, pp. 138–162. [11] H. Chan, U. Ozguner: Closed-loop control of systems over a communication network with queues, Int. J.Control, 62, 3, 493–510 (1995). [12] Y. Xia, G. Liu, D. Rees: H ∞ control for networked control systems in presence of random network delay and data dropout, Proceedings of Chinese Control Conference, 2006, pp. 2030–2034. [13] T. Tarn, N. Xi: Planning and control of internet-based teleoperation, Proceedings of SPIE: Telemanipulator and Telepresence Technologies, 1998, pp. 189–193. [14] P. Baronti, P. Pillai, V. Chook, S. Chessa, A. Gotta, Y. F. Hu: Wireless Sensor Networks: A Survey on the State of the Art and the 802.15.4 and ZigBee Standards, Journal of Computer Communications, 30, 7, 1655–1695 (2007). [15] G. Mouney, G. Juanole, C. Calmettes: On the implementation of one process control application type through a network considering three LANs: CAN, Wi-Fi, ZigBee, 17th OFAC World Congress, 2008. [16] A. Koubaa, M. Alves, Y. Song, B. Nefzi: Improving the IEEE 802.15.4 slotted CSMA-CA for time-critical events in wireless sensor networks, Workshop of Real-time Networks, Satelite workshop for ECRTS, Dresden, Germany, 2006. [17] V. Rao, D. Marandin: Adaptive backoff exponent algorithm for ZigBee, Next Generation Teletraffic and Wired/Wireless Advanced Networking, 2006, pp. 501–516. [18] J. Sobrino, A. Krishnakumar: Quality of service in ad-hoc CSMA networks, IEEE Journal on Selected Areas in Communications, 1999, pp. 1535–1568. [19] U. Umirov, S. Jeong, J. Park: Applicability of ZigBee for real-time networked motor control systems, International Conference on Control, Automation and Systems, Seoul, Korea, 2008. [20] D. Yue, Q. Han, J. Lam: Robust H ∞ control and filtering of networked control systems, Networked Control Systems: Theory and Applications, London: Springer, 2008, pp. 121–151. [21] A. Cervin, M. Ohlin, D. Henriksson: Simulation of networked control systems using TrueTime, Proceedings of the 3rd International Workshop on Networked Control Systems: Tolerant to Faults, 2007

Fractional-order optimal fuzzy control for network delay

Fuzzy logic control has been used frequently in tuning network control system (NCS) due to its on-line dynamic static non-linear match and several remarkable fractional-order controllers have achieved satisfactory control performance when applied to NCS in present years, therefore, in this paper, a novel fractional fuzzy logic controller which combined the fractional algorithm and fuzzy logic control together has been proposed to deal with fixed and random network induced delays in closed-loop feedback systems. The comparisons of set-point tracking performances of fractional fuzzy logic PID controller (FFuzzyPID), conventional fuzzy logic PID controller(FuzzyPID), fractional optimal PID controller (FOPID), and optimal PID controller(OPID) on a representative plant with fixed and random network delays have been shown with simulations. The simulation results indicate that fractional fuzzy logic controller has higher capability to handle network delays compared with other controllers in most cases.

Experimental Evaluation of Novel Master-Slave Configurations for Position Control under Random Network Delay and Variable Load for Teleoperation

This paper proposes two novel master-slave configurations that provide improvements in both control and communication aspects of teleoperation systems to achieve an overall improved performance in position control. The proposed novel master-slave configurations integrate modular control and communication approaches, consisting of a delay regulator to address problems related to variable network delay common to such systems, and a model tracking control that runs on the slave side for the compensation of uncertainties and model mismatch on the slave side. One of the configurations uses a sliding mode observer and the other one uses a modified Smith predictor scheme on the master side to ensure position transparency between the master and slave, while reference tracking of the slave is ensured by a proportional-differentiator type controller in both configurations. Experiments conducted for the networked position control of a single-link arm under system uncertainties and randomly varying network delays demonstrate significant performance improvements with both configurations over the past literature.

Output feedback delay compensation control for networked control systems with random delays

This paper is concerned with the design and analysis problems of output feedback delay compensation controller for networked control systems (NCSs) with random network delay. By taking the full advantage of the packet-based transmission in NCSs, a delay compensation control approach is proposed to actively compensate the network-induced delay in Markovian jump linear system framework. Different from previously reported delay compensation control approaches to NCSs, an output feedback strategy is used to generate the control input packet. A new necessary and sufficient condition is proposed to perform the stability analysis of networked closed-loop system. Furthermore, by using the recently established singular Markovian jump system theory, the controller design problem is solved. Finally, the effectiveness of the proposed method is illustrated by using a numerical example.

Mode-independent fuzzy fault-tolerant variable sampling stabilization of nonlinear networked systems with both time-varying and random delays

This paper develops a fault-tolerant variable sampling control (VSC) scheme for a class of nonlinear networked control systems (NCSs) with time-varying state and random network delays. An uncertain continuous Takagi–Sugeno (T–S) fuzzy system with both state and input varying delays, in the presence of possible actuator faults, is obtained equivalently on the basis of the input delay methodology. A tighter bounding lemma is proposed so as to gain less conservative closed-loop stability criteria. Delay-dependent conditions in terms of linear matrix inequalities are derived for the mode-independent fault-tolerant stabilizing controller of the resulting Markovian network-based system by employing a novel stochastic Lyapunov–Krasovskii (L–K) functional. An illustrative example is simulated to show the validity of the obtained results.

Delay optimal event detection on ad hoc wireless sensor networks

We consider a small extent sensor network for event detection, in which nodes periodically take samples and then contend over a random access network to transmit their measurement packets to the fusion center. We consider two procedures at the fusion center for processing the measurements. The Bayesian setting, is assumed, that is, the fusion center has a prior distribution on the change time. In the first procedure, the decision algorithm at the fusion center is network--oblivious and makes a decision only when a complete vector of measurements taken at a sampling instant is available. In the second procedure, the decision algorithm at the fusion center is network--aware and processes measurements as they arrive, but in a time-causal order. In this case, the decision statistic depends on the network delays, whereas in the network--oblivious case, the decision statistic does not. This yields a Bayesian change-detection problem with a trade-off between the random network delay and the decision delay that is, a higher sampling rate reduces the decision delay but increases the random access delay. Under periodic sampling, in the network--oblivious case, the structure of the optimal stopping rule is the same as that without the network, and the optimal change detection delay decouples into the network delay and the optimal decision delay without the network. In the network--aware case, the optimal stopping problem is analyzed as a partially observable Markov decision process, in which the states of the queues and delays in the network need to be maintained. A sufficient decision statistic is the network state and the posterior probability of change having occurred, given the measurements received and the state of the network. The optimal regimes are studied using simulation.

H ∞ predictive control of networked control systems

This article is concerned with the problem of H ∞ predictive control of networked control system with random network delay. A new control scheme termed networked predictive control is proposed. This scheme mainly consists of the control prediction generator and network delay compensator. While designing the predictor, the control input to the actuator may be different due to networked induced time-delay and data dropout, and two cases are considered depending on the way that the observer obtains the plant control input u t . The necessary and sufficient conditions are given for the closed-loop networked predictive control system to be stochastically stable for different u t and random network delays in controller to actuator channel (CAC) and sensor to controller channel (SCC). A simulation study shows the effectiveness of the proposed scheme.

Control Over Imperfect Networks: Model-Based Predictive Networked Control Systems

Networked control systems (NCSs) are digital control systems in which the functionality of the sensor, control, and actuator reside in physically different computer nodes communicating over a network. However, random delays and data loss of the communication network can endanger the stability of an NCS. We have proposed model-based predictive NCSs (MBPNCSs) that compensate for the aforementioned problems and avoid performance loss using a predictive control scheme based on a model of the plant. There are three main contributions of this paper to existing methods: an NCS that can work under random network delay and data loss with realistic structural assumptions, an explicit mechanism for reducing the effects of network delay and data loss on the deviation of plant state estimates from actual plant states, and an architecture where upstream nodes can work without receiving acknowledge information about the status of previously sent data packets from downstream nodes. In this paper, we describe MBPNCS and then introduce a stability criterion. This is followed by computer simulations and experiments involving the speed control of a dc motor. The results show that considerable improvement over performance is achieved with respect to an event-based NCS.

A Robust Approach for Clock Offset Estimation in Wireless Sensor Networks

The maximum likelihood estimators (MLEs) for the clock phase offset assuming a two-way message exchange mechanism between the nodes of a wireless sensor network were recently derived assuming Gaussian and exponential network delays. However, the MLE performs poorly in the presence of non-Gaussian or nonexponential network delay distributions. Currently, there is a need to develop clock synchronization algorithms that are robust to the distribution of network delays. This paper proposes a clock offset estimator based on the composite particle filter (CPF) to cope with the possible asymmetries and non-Gaussianity of the network delay distributions. Also, a variant of the CPF approach based on the bootstrap sampling (BS) is shown to exhibit good performance in the presence of reduced number of observations. Computer simulations illustrate that the basic CPF and its BS-based variant present superior performance than MLE under general random network delay distributions such as asymmetric Gaussian, exponential, Gamma, Weibull as well as various mixtures.

A new networked predictive control approach for systems with random network delay in the forward channel

This article is concerned with the design of a networked predictive control (NPC) scheme with random network delay in the forward channel. A new design method of NPC is proposed. Correspondingly, the necessary and sufficient conditions on the stability of the closed-loop networked control system are derived. The merit of the proposed design method lies in its decreased conservativeness, which is achieved by packing the current predictive control signal with history predictive signals. By this means, the future plant input is known. Therefore, the state predictor can be designed such that its performance and stability will not be affected by the future input of the plant, while the existing design methods of NPC cannot do so. The proposed design method is shown to be much less conservative than the existing result through several examples.

Predictive control and scheduling codesign in network control systems

A codesign approach combining predictive control compensation and network scheduling is presented in this paper to overcome the adverse influences of stochastic time delays and packet losses encountered in network-based real-time control systems. The state estimation and control prediction compensation algorithms are used for the random network delays in the feedback and forward channels, and the stability criteria are analyzed. The proper sampling rate is given with network scheduling to meet the desired system performance, while the network-induced delay is tolerated. Simulations show that the codesign approach works well with the bounded network delay.

Predictive control of networked systems with random delay and data dropout

This study is concerned with the stochastic stability analysis of networked control systems with random network delay. A new control scheme termed networked predictive control is proposed. This scheme mainly consists of the control prediction generator and network-delay compensator. The control prediction generator provides a set of future control predictions to make the closed-loop system achieve the desired control performance and the network-delay compensator removes the effects of the network transmission delay and data dropout. The stochastic stability criteria of the closed-loop networked predictive control systems are derived. A numerical example and a practical experiment are given to show the potential of the proposed techniques.

A robust estimation scheme for clock phase offsets in wireless sensor networks in the presence of non-Gaussian random delays

To cope with the Gaussian or non-Gaussian nature of the random network delays, a novel method, referred to as the Gaussian mixture Kalman particle filter (GMKPF), is proposed herein to estimate the clock offset in wireless sensor networks. GMKPF represents a better and more flexible alternative to the symmetric Gaussian maximum likelihood (SGML), and symmetric exponential maximum likelihood (SEML) estimators for clock offset estimation in non-Gaussian or non-exponential random delay models. The computer simulations illustrate that GMKPF yields much more accurate results relative to SGML and SEML when the network delays are modeled in terms of a single non-Gaussian/non-exponential distribution or as a mixture of several distributions.

Networked predictive control of systems with random delay in signal transmission channels

This article considers the design and stability of networked control systems with random delay in signal transmission channels. To deal with the random delay, a networked predictive control strategy is proposed for discrete networked systems. The key parts of the control strategy are the control prediction generator that provides a set of future control predictions and the network delay compensator that compensates for the network transmission delay. The analytical stability criteria of the closed-loop networked predictive control systems are derived for both fixed and random network delays. The proposed networked predictive control method is illustrated using simulations and practical Intranet-/Internet-based control experiments.

Predictive Control Strategy for a Wireless Networked System

As the technology matures, wireless networks are being widely used in industry and homes providing mobile users with significant benefits. In this paper, a networked recursive predictive control method is proposed for the general packet radio service (GPRS) wireless network. Such an implementation has a long random network delay and high data dropout rates. Practical experiments have been carried out to demonstrate the effectiveness of the proposed predictive control scheme.

Design and Practical Implementation of Internet-Based Predictive Control of a Servo System

This brief discusses the design and practical implementation of an Internet-based predictive control strategy. This novel control strategy can compensate for the random network delay and data dropout in an active way. In order to test the performance of the proposed control scheme, the offline simulation and practical implementation of an Internet-based servo control system are carried out. At the same time, the stability of the control scheme is also studied. The simulation and experimental results illustrate the feasibility and efficiency of the proposed Internet-based predictive control scheme.

Networked Predictive Control of Systems With Random Network Delays in Both Forward and Feedback Channels

The design problem of networked control systems (NCS) with constant and random network delay in the forward and feedback channels, respectively, is considered in this paper. A novel networked predictive control (NPC) scheme is proposed to overcome the effects of network delay and data dropout. Stability criteria of closed-loop NPC systems are presented. The necessary and sufficient conditions for the stability of closed-loop NCS with constant time delay are given. Furthermore, it is shown that a closed-loop NPC system with bounded random network delay is stable if its corresponding switched system is stable. Both simulation study and practical experiments show the effectiveness of the control scheme

Design and Stability Criteria of Networked Predictive Control Systems With Random Network Delay in the Feedback Channel

This paper is concerned with the design of networked control systems (NCSs) with random network delay in the feedback channel and gives stability criteria of closed-loop networked predictive control systems. The principle of predictive control is adopted to overcome the effects of network time delay. The necessary and sufficient conditions on the stability of the closed-loop NCS are derived, which provides useful analytical stability criteria. The closed-loop networked predictive control system with bounded random network delay is stable if the corresponding switched system is stable. Simulation and real-time results give an illustration of the proposed control strategies

QoS-Based Remote Control of Networked Control Systems Via Profibus Token Passing Protocol

This paper focuses on a quality-of-service (QoS)-based remote control scheme for networked control systems via the Profibus token passing protocol. Typically, token passing experiences random network delay due to uncertainties in token circulation, but the protocol has in-built upper and lower bounds of network delay. Thus, to ensure the control performance of networked control systems via the Profibus token passing protocol, the network delay should be maintained below the allowable delay level. As the network delay is affected by protocol parameters, such as target rotation time, we present here an algorithm for selection of target rotation time using a genetic algorithm to ensure QoS of control information. We also discuss the performance of the QoS-based remote control scheme under conditions of controlled network delay. To evaluate its feasibility, a networked control system for a feedback control system using a servo motor was implemented on a Profibus-FMS network.