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Time filter

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Moayedi M.,Nanyang Technological University | Foo Y.K.,LW Electrical and Mechanical Engineering Private Ltd | Soh Y.C.,Nanyang Technological University
International Journal of Systems Science | Year: 2011

The minimum-variance filtering problem in networked control systems, where both random measurement transmission delays and packet dropouts may occur, is investigated in this article. Instead of following the many existing results that solve the problem by using probabilistic approaches based on the probabilities of the uncertainties occurring between the sensor and the filter, we propose a non-probabilistic approach by time-stamping the measurement packets. Both single-measurement and multiple measurement packets are studied. We also consider the case of burst arrivals, where more than one packet may arrive between the receiver's previous and current sampling times; the scenario where the control input is non-zero and subject to delays and packet dropouts is examined as well. It is shown that, in such a situation, the optimal state estimate would generally be dependent on the possible control input. Simulations are presented to demonstrate the performance of the various proposed filters. © 2011 Taylor & Francis. Source


Foo Y.K.,LW Electrical and Mechanical Engineering Private Ltd | Moayedi M.,Nanyang Technological University | Soh Y.C.,Nanyang Technological University
International Journal of Systems Science | Year: 2015

This article addresses the linear quadratic Gaussian (LQG) control problem of networked multi-input, multi-output systems where computational delay exists and the measurement and control signals are packetised and transmitted through a network within which random delay and packet loss may occur during transmissions. A transmission control protocol (TCP)-like protocol for the communication network is considered in which acknowledgement is sent from the actuator to the controller if and only if the control packet is received, assuming these acknowledgements always reach the estimator in time and without fail. To minimise the data word-length for transmissions over the network and to maximise control system performance, it is proposed that different quantisation resolutions be used for transmission data encapsulation, and control and output signals A/D-D/A conversions at sensor/actuator. To circumvent the problem of disparity between encapsulation and A/D-D/A quantisation resolutions, a pseudo-stochastic approach via subtractive dither is applied to quantise the transmission packets. This also enables us to model the quantisation errors as uncorrelated independent zero-mean additive white noises and apply standard LQG methodology and separation principle to design the estimator and the controller separately. An example is included to demonstrate the effectiveness of the approach. © 2014 Taylor & Francis Source


Moayedi M.,Nanyang Technological University | Foo Y.K.,LW Electrical and Mechanical Engineering Private Ltd | Soh Y.C.,Nanyang Technological University
Proceedings of the IEEE Conference on Decision and Control | Year: 2010

In this article the Linear Quadratic Gaussian (LQG) optimal control problem for networked control systems when data is transmitted through a TCP-like network and both measurement and control packets are subject to random packet dropouts, is addressed for two cases. In the first case it is assumed that the control acknowledgment packets in TCP-like protocols are always available and we pròpose how to design a linear optimal "hold-input" control law for this case. In the second problem, we assume the acknowledgement packets may go missing with a known probability. We derive a suboptimal linear estimation-control law for this part. Simulation results are presented to demonstrate the effectiveness of the proposed approaches. ©2010 IEEE. Source


Foo Y.K.,LW Electrical and Mechanical Engineering Private Ltd
International Journal of Systems Science | Year: 2013

The robust stability of large-scale interconnected systems in the presence of block-structured additive perturbations is studied. It is shown that a Gershgorin-like result is applicable for the analysis of such systems. Based on insight derived from such analysis, a conceptual approach based on the characteristic loci technique is proposed for the design of robust decentralised controller for such systems. © 2013 Taylor & Francis Group, LLC. Source


Moayedi M.,Nanyang Technological University | Foo Y.K.,LW Electrical and Mechanical Engineering Private Ltd | Soh Y.C.,Nanyang Technological University
IEEE Transactions on Signal Processing | Year: 2010

In this paper, adaptive filtering schemes are proposed for state estimation in sensor networks and/or networked control systems with mixed uncertainties of random measurement delays, packet dropouts and missing measurements. That is, all three uncertainties in the measurement have certain probability of occurrence in the network. The filter gains can be derived by solving a set of recursive discrete-time Riccati equations. Examples are presented to demonstrate the applicability and performances of the proposed schemes. © 2010 IEEE. Source

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