Timing problems in real-time control systems
21 Jun 1995-Vol. 3, pp 2000-2004
TL;DR: The paper formulates and discusses timing problems in real-time systems from the sampled data point of view and different ways to eliminate the effects of communication delays are considered.
Abstract: The paper formulates and discusses timing problems in real-time systems from the sampled data point of view. Different ways to eliminate the effects of communication delays are considered.
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Dissertation•
01 Jan 1998
TL;DR: In the thesis it is shown how to analyze stability and expected performance of linear controllers where the network delays are described by one of the two network models above.
Abstract: Control loops that are closed over a communication network get more and more common. A problem with such systems is that the transfer delays will be varying with different characteristics depending on the network hardware and software. The network delays are typically varying due to varying network load, scheduling policies in the network and the nodes, and due to network failures. Two network models of different complexity are studied: Random delays that are independent from transfer to transfer, Random delays with probability distribution functions governed by an underlying Markov chain. The delay models are verified by experimental measurements of network delays. In the thesis it is shown how to analyze stability and expected performance of linear controllers where the network delays are described by one of the two network models above. Methods to evaluate quadratic cost functions are developed. Through the same analysis we find criteria for mean square stability of the closed loop for the different network models. The Linear Quadratic Gaussian (LQG) optimal controller is developed for the two delay models. The derived controller uses knowledge of old time delays. These can be calculated using ``timestamping'' of messages in the network. ``Timestamping'' means that every transfered signal is marked with the time of generation. The receiving node can then calculate how long the transfer delay was by comparing the timestamp with the node's internal clock. (Less)
1,202 citations
TL;DR: The main methodologies suggested in the literature to cope with typical network-induced constraints, namely time delays, packet losses and disorder, time-varying transmission intervals, competition of multiple nodes accessing networks, and data quantization are surveyed.
Abstract: Networked control systems (NCSs) have, in recent years, brought many innovative impacts to control systems. However, great challenges are also met due to the network-induced imperfections. Such network-induced imperfections are handled as various constraints, which should appropriately be considered in the analysis and design of NCSs. In this paper, the main methodologies suggested in the literature to cope with typical network-induced constraints, namely time delays, packet losses and disorder, time-varying transmission intervals, competition of multiple nodes accessing networks, and data quantization are surveyed; the constraints suggested in the literature on the first two types of constraints are updated in different categorizing ways; and those on the latter three types of constraints are extended.
989 citations
TL;DR: In this article, a new scheme based on stochastic control theory and a separation property is shown to hold for the optimal controller for real-time systems subject to random time delays in the communication network is presented.
918 citations
TL;DR: A stochastic packet-loss model for the network is used and results for discrete-time linear systems with Markovian jumping parameters can be applied to study the effect of communication losses on vehicle control.
Abstract: In this paper, we study the effect of a network in the feedback loop of a control system. We use a stochastic packet-loss model for the network and note that results for discrete-time linear systems with Markovian jumping parameters can be applied. We measure performance using an H/sub /spl infin// norm and compute this norm via a necessary and sufficient matrix inequality condition. We also derive necessary and sufficient linear matrix inequality (LMI) conditions for the synthesis of the H/sub /spl infin// optimal controller for a discrete-time jump system. Finally, we apply these results to study the effect of communication losses on vehicle control.
729 citations
Cites background from "Timing problems in real-time contro..."
...Control synthesis results for NCSs have employed linear quadratic Gaussian (LQG) style costs, [7], -synthesis [19], [48], observers to compensate for delays [15], [33], [50], and results for stochastic jump systems...
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TL;DR: A new scheme for handling the random time delays is developed and successfully compared with previous schemes, based on stochastic control theory and a separation property is shown to hold for the optimal controller.
420 citations
References
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TL;DR: The delayed control system is represented by a finitedimensional, time-varying, discrete-time model which is less complex than the ex isting continuous-time models for time- varying delays; this approach allows for simpler schemes for analysis and simulation of ICCS.
Abstract: The paper presents the results of an ICCS analysis focusing on discrete-time control systems subject to time-varying delays. The present analytical technique is applicable to integrated dynamic systems such as those encountered in advanced aircraft, spacecraft, and the real-time control of robots and machine tools via a high-speed network within an autonomous manufacturing environment. The significance of data latency and missynchronization between individual system components in ICCS networks is discussed in view of the time-varying delays.
565 citations
TL;DR: A new scheme for handling the random time delays is developed and successfully compared with previous schemes, based on stochastic control theory and a separation property is shown to hold for the optimal controller.
420 citations
TL;DR: This observer-based algorithm is specially suited to compensation of network-induced delays in integrated communication and control systems.
419 citations
"Timing problems in real-time contro..." refers background or methods in this paper
...Make the System Time-Invariant In Luck and Ray (1990) the closed loop system is made time-invariant by introduction of buffers at the controller and actuator nodes as illustrated in Figure 1....
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...In Luck and Ray (1990) the LQG-optimal controller, uk ξ (Wk), is derived....
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TL;DR: A state prediction/control scheme to control closed loop control through a communication network that uses knowledge of the amount of data in the queue to enhance prediction and demonstrate the performance of the proposed scheme.
Abstract: Due to remote sensor, actuator and processor locations, many systems need to implement closed loop control through a communication network. Thus, they may thus face the problem of induced random delays caused by the network. These delays may deteriorate the system performance and may even cause instability. The problems get more complicated when the possibility of queue formation at the transmitting side is considered for closed loop data transmission. In this paper, we propose a state prediction/control scheme to control this type of system. The scheme utiliźes knowledge of the amount of data in the queue to enhance prediction. Two automotive examples will be used to demonstrate the performance of the proposed scheme.
168 citations
TL;DR: In this article, an estimation and control law for delay compensation is built on the concept of the conventional linear quadratic Gaussian (LQG), which is called delay compensated LQG (DCLQG).
Abstract: An output feedback control law has been formulated in a stochastic setting, based on the principles of minimum variance filtering and dynamic programming, for application to processes that are subjected to randomly varying distributed delays. The proposed estimation and control law for delay compensation is built on the concept of the conventional linear quadratic Gaussian (LQG), called delay compensated linear quadratic Gaussian (DCLQG). Although the certainty equivalence property of LQG does not hold for DCLQG in general, the combined state estimation and state feedback approach of DCLQG offers a suboptimal solution to the control problem under randomly varying distributed delays. DCLQG is potentially applicable to analysis and synthesis of control systems for vehicle management of future generation aircraft where a computer network is employed for distributed processing and on-line information exchange between diverse control and decision-making functions. Results of simulation experiments are presented to demonstrate efficacy of the proposed DCLQG algorithm for flight control of an advanced aircraft.
150 citations